The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the d...The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.展开更多
By using the traveling wave method, the solutions of the elliptic function wave and the solitary wave are obtained in a ferromagnetic spin chain with a biquadratic exchange interaction, a single ion anisotropic intera...By using the traveling wave method, the solutions of the elliptic function wave and the solitary wave are obtained in a ferromagnetic spin chain with a biquadratic exchange interaction, a single ion anisotropic interaction and an anisotropic nearest neighbour interaction. The effects of the biquadratic exchange interaction and the single ion anisotropic interaction on the properties （width, peak and stability） of the soliton are investigated. It is also found that the effects vary with the strengths of these interactions.展开更多
Effects of the intergrain exchange interaction on magnetic properties of nanocomposite magnets were investigated by using the computer simulation based on the micromagnetic theory. The simulation was carried out unde...Effects of the intergrain exchange interaction on magnetic properties of nanocomposite magnets were investigated by using the computer simulation based on the micromagnetic theory. The simulation was carried out under the assumptions that the strength of the intergrain exchange interaction is weaker than that of the intragrain exchange interaction, that inhomogeneous nanostructures result in the distribution of the strength of the intergrain exchange interaction, and that there exists nonmagnetic intergranular phase (NMIP) between grain boundaries. The distribution of the strength of the intergrain exchange interaction was simulated by the lognormal distribution with the standard deviation of σ.The calculations for Nd 2Fe 14B/α-Fe nanocomposite magnets reveal that a suitably weak intergrain exchange interaction and small grain size enable us to improve magnetic properties. It is also found that a Nd 2Fe 14B/α-Fe nanocomposite magnet has a potential of a (BH) max value exceeding 300 kJ·m -3. On the other hand, the calculations for Nd 2Fe 14B/Fe 3B nanocomposite magnets reveal that the distribution of the strength of the intergrain exchange interaction deteriorates magnetic properties significantly. Particularly, this tendency is remarkable, when the grain size L is larger than its optimum value, 11 nm. The existence of nonmagnetic boundary layers accelerats this tendency. At σ=0.2, the calculated demagnetization curve for the model magnet composed of Nd 2Fe 14B(36%)/Fe 3B(54%)/NMIP(10%) (Valume fraction) grains (L=15 nm) agrees with that obtained experimentally for a Nd 2Fe 14B/Fe 3B nanocomposite magnet. These results suggest importance of refinement of grain size, suppression of a nonmagnetic intergranular phase, and preparation of homogeneous nanostructure for superior magnetic properties.展开更多
Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co （and Fe65Co35） magnetic films ...Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co （and Fe65Co35） magnetic films was characterized by measuring static （mr（H）） and demagnetized （md（H）） remanence curves. According to conventional method： δm（H）=md（H） - [1 - 2mr（H）], the exchange interaction was evaluated. The switching fields H′p and Hp, at which static （mr（H）） and demagnetized （md（H）） remanence show the fastest change, were identified. The relative ratio η=Hp-H′p/Hp of switching fields H′p and Hp has a linear relationship with the maximum value δmmax of δm（H） curves, proposing an alternative way to characterize the exchange interaction.展开更多
This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions （low temperatures and high magnetic field...This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions （low temperatures and high magnetic fields） based on quantum theory. Here, five sets of crystal field parameters are discussed and compared. It demonstrates that, only considering the crystal field effect, the experiments can not be successfully explained. Thus, referring to the molecular field theory, an effective exchange field associated with the Dy-Dy exchange interaction is further taken into account. Under special consideration of crystal field and the exchange interaction field, it obtains an excellent agreement between the theoretical results and experiments, and further confirms that the exchange interaction field between rare-earth ions has great importance to magnetic properties in paramagnetic rare-earth gallium garnets.展开更多
The dependences of spin wave resonance(SWR)frequency on the surface anisotropy field,interface exchange coupling,symmetry,biquadratic exchange(BQE)interaction,film thickness,and the external magnetic field in bilayer ...The dependences of spin wave resonance(SWR)frequency on the surface anisotropy field,interface exchange coupling,symmetry,biquadratic exchange(BQE)interaction,film thickness,and the external magnetic field in bilayer ferromagnetic films are theoretically analyzed by employing the linear spin wave approximation and Green’s function method.A remarkable increase of SWR frequency,except for energetically lower two modes,can be obtained in our model that takes the BQE interaction into account.Again,the effect of the external magnetic field on SWR frequency can be increased by increasing the biquadratic to interlayer exchange ratio.It has been identified that the BQE interaction is of utmost importance in improving the SWR frequency of the bilayer ferromagnetic films.In addition,for bilayer ferromagnetic films,the frequency gap between the energetically highest mode and lowest mode is found to increase by increasing the biquadratic to interlayer exchange ratio and film thickness and destroying the symmetry of the system.These results can be used to improve the understanding of magnetic properties in bilayer ferromagnetic films and thus may have prominent implications for future magnetic devices.展开更多
Electron spins confined in semiconductor quantum dots(QDs)are one of potential candidates for physical implementation of scalable quantum information processing technologies.Tunnel coupling based inter exchange intera...Electron spins confined in semiconductor quantum dots(QDs)are one of potential candidates for physical implementation of scalable quantum information processing technologies.Tunnel coupling based inter exchange interaction between QDs is crucial in achieving single-qubit manipulation,two-qubit gate,quantum communication and quantum simulation.This review first provides a theoretical perspective that surveys a general framework,including the Helter−London approach,the Hund−Mulliken approach,and the Hubbard model,to describe the inter exchange interactions between semiconductor quantum dots.An electrical method to control the inter exchange interaction in a realistic device is proposed as well.Then the significant achievements of inter exchange interaction in manipulating single qubits,achieving two-qubit gates,performing quantum communication and quantum simulation are reviewed.The last part is a summary of this review.展开更多
In present investigation exchange interactions of Pr_(n+1)Co_(3n+5)B_(2n)-type compounds have been evalu- ated in the light of molecular-field theory. The exchange interactions and ferromagnetism in these compounds ar...In present investigation exchange interactions of Pr_(n+1)Co_(3n+5)B_(2n)-type compounds have been evalu- ated in the light of molecular-field theory. The exchange interactions and ferromagnetism in these compounds are discussed in terms of lattice parameters and interatomic distance between Co atom.展开更多
The dynamic properties of interacting vortex-antivortex pairs in thin film are studied by analytical calculations. An- alytical expressions for the magnetization vector distribution of vortex-antivortex pairs and the ...The dynamic properties of interacting vortex-antivortex pairs in thin film are studied by analytical calculations. An- alytical expressions for the magnetization vector distribution of vortex-antivortex pairs and the trivortex states are given. The magnetic states of the vortices are treated as having rigid structures, i.e., the vortex maintains its spin distribution when moving. The trajectories of the vortex cores are calculated by the Thiele＇s equation. It is found that the vortex-antivortex pair rotates around each other when they have opposite polarities, however, vortex and antivortex cores move along straight lines when they have the same polarity. The frequency of the rotation decreases with increasing the distance between the two cores of vortex-antivortex pair, and it has a lower value when a third vortex is introduced.展开更多
Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-...Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-troscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field,Hhf , demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton Am increases with increasing Co content. The saturation magnetostriction λs decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of Am. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.展开更多
SmCo/FeCo/SmCo trilayer was deposited with two different thickness configurations for soft phase (FeCo);50 nm/10 nm/50 nm and 50 nm/25 nm/50 nm were deposited on Si (111) substrate and Ta (50 nm) seed layer by RF magn...SmCo/FeCo/SmCo trilayer was deposited with two different thickness configurations for soft phase (FeCo);50 nm/10 nm/50 nm and 50 nm/25 nm/50 nm were deposited on Si (111) substrate and Ta (50 nm) seed layer by RF magnetron sputtering in a pressure, p, of 30 - 35 m Torr. After deposition the films were annealed under Ar atmosphere at temperature T equal to 923 and 973 for different times followed by quenching in water. X-ray diffraction patterns were obtained to identified phase presents and calculate average crystallite size. To study the effect of configuration thickness in soft phases, DC magnetic measurements were carried out;the measurements were done in the temperature interval of 300 - 50 K. Hysteresis loops collected at low temperatures exposed an increment in coercivity with the decrease of T and at same time, presented a “knee” in the second quadrant of the demagnetization curve, which suggests that the inter-layer exchange coupling becomes less effective, being more evident for sample with 50 nm/25 nm/50 nm thickness. Moreover, δM (H) plots were calculated from magnetic measurements at three different temperatures, T, equal to 300, 150 and 50 K, which corroborates that the dipolar interactions became stronger when thickness of soft phases increases. Finally, the thickness effect is attributed to the SmCo5 phase magnetocrystalline anisotropy constant, which is responsible for the exchange coupling length.展开更多
Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coe...Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coefficient B20 and the magnetic exchange interaction was studied as temperature approaches to 0 K. The results show that the stabilization energy contributed by Tb3+ is linear with crystal field coefficient B20 approximately, but it is insensitive to the change of magnetic exchange interaction for the strong magnetic substances such as TbCo5, Tb2Co17 and Tb2Fe14B compounds.展开更多
A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found...A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found to display single-molecule magnetism(SMM)behaviour with a Ueff=54 cm^(−1)and well-resolved magnetisation hysteresis plots,with a blocking temperature,T_(B)=3.5 K.In the present study,fourteen related{Cr^(Ⅲ)2 Dy^(Ⅲ)_(2)}complexes have been synthesised,and their magnetic properties have been studied.The study probes how chemical changes in bridging ligands and coordination environment affect the SMM properties compared to the parent complex.We show that by making simple chemical modifications to the ligands,the Ueff and T_(B)values change,with Ueff values ranging from 22 to 65 cm^(−1)and T_(B)1.8 K to 4.7 K.We also show that SMM behaviour can be turned off by manipulation of the coordination sphere around the Dy^(Ⅲ)ion.Based on these experimental results,we undertook a detailed theoretical study to understand why these changes occur.The theoretical studies further describe the mode of exchange mechanism in such complexes and how it controls the blocking temperature.Further,we have found that the exchange coupling between the Dy^(Ⅲ)–Cr^(Ⅲ)ions strongly influences the magnetic relaxation for this family of complexes,and interestingly,the exchange between the Cr^(Ⅲ)–Cr^(Ⅲ)centres plays a determining role in the overall SMM properties,which has been ignored in previous studies.We have derived a relation between the magnetic exchange and T_(B)for such 3d–4f SMMs where exchange coupled states play a dominant role,revealing the blocking temperature is strongly correlated to the overall magnetic exchange.This clearly illustrates the importance of inducing strong exchange coupling to enhance not only the magnetisation reversal barrier but also T_(B)via quenching of zero-field quantum tunnelling of the magnetisation(QTM)in{3d–4f}type complexes.展开更多
The performance of Single-Molecule Magnets(SMMs)can be enhanced by reducing quantum tunneling of magnetization(QTM),which can be achieved with the aid of strong magnetic exchange interactions and strong magnetic aniso...The performance of Single-Molecule Magnets(SMMs)can be enhanced by reducing quantum tunneling of magnetization(QTM),which can be achieved with the aid of strong magnetic exchange interactions and strong magnetic anisotropy.When 4d ions are mixed with 4f ions,the strong spin–orbit coupling and moderate ligand-field strength of 4d elements complement the highly anisotropic 4f ions,and the combined effect decreases the transverse anisotropy and stabilizes the magnetic easy axis,both of which are essential for lowering QTM.Despite their synthetic challenges,the unique electronic properties of 4d–4f systems make them promising candidates for designing advanced single-molecule magnets.Here,we report the synthesis,magnetic,and theoretical studies of five tetranuclear“butterfly-shaped”complexes of formulae[Ru^(Ⅲ)_(2)Ln^(Ⅲ)_(2)(OMe)_(2)(o-tol)_(4)(mdea)_(2)(NO_(3))_(2)](Ln=Gd(1-Gd),Tb(2-Tb),Dy(3-Dy),Ho(4-Ho),mdeaH2=N-methyldiethanolamine)and[Ru^(Ⅲ)_(2)Er^(Ⅲ)_(2)(OMe)_(2)(o-tol)6(mdea)_(2)]·2MeOH(5-Er).Complexes 2-Tb,4-Ho,and 5-Er are the first reported examples of Ru-4f complexes using these Ln^(Ⅲ)ions.DC magnetic susceptibility studies revealed an antiferromagnetic exchange interaction between the Ln^(Ⅲ)and Ru^(Ⅲ)metal ions in all complexes.Among the complexes reported,3-Dy and 4-Ho show out-of-phase susceptibility signals in the absence of an external magnetic field,while the remaining complexes exhibit field-induced slow relaxation of magnetization.These observations were attributed to the presence of an ideal crystal field combined with the strong exchange interaction exerted between the Ru^(Ⅲ)and Ln^(Ⅲ)ions in the complexes.Importantly,the 4-Ho is the first non-dysprosium Ru–Ln polynuclear complex to show zero-field SMM behavior.Detailed ab initio CASSCF+RASSI-SO+SINGLE_ANISO+POLY_ANISO and Density Functional Theory(DFT)calculations reveal that the magnitude of exchange interaction increases in the following order:1-Gd(−1.3 cm^(−1))<2-Tb(−1.8 cm^(−1))<3-Dy(−2.7 cm^(−1))<4-Ho(−2.8 cm^(−1))<5-Er(−4.0 cm^(−1)).The larger single-ion anisotropy of the DyⅢions in 3-Dy leads to the largest barrier of 101.8 cm^(−1)(146 K),which increases further to 111 cm^(−1)(158.7 K)when considering the exchange-coupled model,with the strong Ru⋯Ln exchange further quenching QTM effects.These results highlight the importance of strong magnetic exchange between 4d–4f(Ru^(Ⅲ)⋯Ln^(Ⅲ))ions in enhancing the SMM behavior of 4d–4f complexes.展开更多
Single-ion magnets(SIMs)are the most promising candidates for magnetic storage and processing of information at the molecular level.Apart from the properties of each isolated SIM,their performance crucially depends on...Single-ion magnets(SIMs)are the most promising candidates for magnetic storage and processing of information at the molecular level.Apart from the properties of each isolated SIM,their performance crucially depends on intermolecular exchange interactions in bulk materials or those occurring when individual SIMs are assembled into arrays for practical applications.However,compared with their magnetic anisotropy,the correlation of in-bulk intermolecular exchange interactions and magnetic relaxation parameters has been established to a much lesser extent.In this work,using an extended protocol involving XRD,multifrequency and frequency-domain EPR,SQUID magnetometry,DFT and ab initio calculations,we investigated intermolecular interactions in a new series of four bis-(phenoxy Schiff base)Co(Ⅱ)complexes representing field-induced SIMs.Combined multifrequency EPR ranging from 9 GHz to>1 THz allowed unique measurement of weak intermolecular exchange couplings of the order of 0.01 cm^(-1).Consolidation of EPR data with ac/dc SQUID magnetometry and detailed structural and quantum-chemical analyses allowed us to reliably analyze the key performance characteristics of these SIMs,the degree of polyhedral distortion,and the values of intermolecular exchange couplings in an attempt to achieve a firm interplay among them.Such analysis can become prototypical for future design and evaluation of crystals,assemblies and arrays of SIMs.展开更多
We report the synthesis and characterization of two symmetric homo-dimetallic lanthanide complexes based on methyl-substituted 8-hydroxyquinoline(HMeQ).The aryloxo-bridged core gives rise to weak magnetic coupling bet...We report the synthesis and characterization of two symmetric homo-dimetallic lanthanide complexes based on methyl-substituted 8-hydroxyquinoline(HMeQ).The aryloxo-bridged core gives rise to weak magnetic coupling between pairs of ErⅢand YbⅢions,as revealed by magnetic and EPR spectroscopy studies.EPR measurements of magnetically dilute species,coupled with CASSCF-SO calculations,allows modelling of the EPR spectra of the exchange coupled species and the magnetic data simultaneously.This work adds to the database of exchange coupled{Ln}_(2)molecules which have been thoroughly characterised by EPR spectroscopy and modelled using an S_(eff)=1/2 approach to describe the interaction of ground Kramers states,and highlights the differences between centro-symmetric and asymmetric dimetallics.展开更多
The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study,...The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.展开更多
The 2:14:1-type rare-earth(RE)-Fe-B permanent magnets prepared by the dual alloy method have been found to possess much superior magnetic properties to those prepared by the single alloy method,providing an appealing ...The 2:14:1-type rare-earth(RE)-Fe-B permanent magnets prepared by the dual alloy method have been found to possess much superior magnetic properties to those prepared by the single alloy method,providing an appealing route to promote the utilization of high-abundance RE elements Ce and La and balance the use of the RE source.However,the relationship between magnetic interactions among different 2:14:1 main phases and superior magnetic properties is still unclear.In this study,we investigated the magnetic interactions and reversal field distribution in these magnets using first-order reversal curve(FORC)images.The FORC images showed that(Nd,Pr)27.8(La,Ce)2.7FebalM1.4B1.0(S-9)and(Nd,Pr)19.5(La,Ce)11.0FebalM1.4B1.0(S-36)have the characteristics of multiple main phases.The reverse magnetic fields corresponding to the soft and hard main phases,as well as the associated exchange coupling,were highly dependent on the La Ce content.The higher the La Ce content,the weaker the exchange coupling and the more asynchronous the demagnetization process.In addition,the FORC images indicated that the magnetization reversal process also varies with La Ce content,where the nucleation and propagation of reversed domains dominant in the S-9 magnet,while the domain propagation in the S-36 magnet is considerably suppressed.Additional micromagnetic simulations also revealed that the coercivity and exchange coupling of multi-main-phase magnets decrease with increasing La Ce content,correlating well with the experimental results.These findings may not only contribute to a better understanding of the complex magnetic interactions between the soft and hard phases and how they affect macroscopic magnetic properties but also help in improving the magnetic performance of the RE-Fe-B magnets with high La Ce content.展开更多
A novel heterospin complex {[(CuL)Ni(IM 2Py) 2](ClO 4) 2} 2·2H 2O (L=2,3 dioxo 5,6:14,15 dibenzo 1,4,8,12 tetraazacyclo pentadeca 7,12 diene, IM 2Py=2 (2′ pyridyl) 4,4,5,5 tetra^methyl 4,5 d...A novel heterospin complex {[(CuL)Ni(IM 2Py) 2](ClO 4) 2} 2·2H 2O (L=2,3 dioxo 5,6:14,15 dibenzo 1,4,8,12 tetraazacyclo pentadeca 7,12 diene, IM 2Py=2 (2′ pyridyl) 4,4,5,5 tetra^methyl 4,5 dihydro 1 H imidazoline 1 oxyl) has been synthesized and its crystal structure was determined by X ray diffraction analysis. In order to interpret the exchange interaction of this asymmetric heterospin system, a theoretical model has been established. Using this theoretical model the magnetic susceptibility data have been fitted and lead to coupling constant values equal to 1 4 cm -1 (Ni Rad) and -38 0 cm -1 (Ni Cu), respectively.展开更多
The influence of annealing time on the magnetic properties and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons was systematically investigated by the methods of vibrating sample magnetometer （VSM）, ...The influence of annealing time on the magnetic properties and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons was systematically investigated by the methods of vibrating sample magnetometer （VSM）, X-ray diffraction （XRD） and high resolution transmission electron microscopy （HRTEM）. Interaction domains derived from strong exchange coupling interactions between hard and soft magnetic grains were imaged using magnetic force microscopy （MFM）. Maximum remanence, intrinsic coercivity, and maximum energy product values were obtained in the ribbons annealed at 700℃ for 15 min, which were composed of Pr2（Fe, Co）14B, α-（Fe, Co）, and slight Pr2（Fe, CO）17 phases. Although Jr, Hci, and （Bn）max decreased gradually with further increase of annealing time, it is emphasized that comparatively high Jr and Hci and （BH）max were obtained in a wide annealing time period of 15 to 360 min. The shape of initial magnetization curves and hysteresis loops change as a function of annealing time, indicating different magnetization reversal routes, which can be fully explained by the corresponding microstructure.展开更多
基金Project supported by the Science and Technology Foundation of China University of Mining and Technology (Grant No OK061066)
文摘The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10874049)the State Key Program for Basic Research of China (Grant No. 2007CB925204).
文摘By using the traveling wave method, the solutions of the elliptic function wave and the solitary wave are obtained in a ferromagnetic spin chain with a biquadratic exchange interaction, a single ion anisotropic interaction and an anisotropic nearest neighbour interaction. The effects of the biquadratic exchange interaction and the single ion anisotropic interaction on the properties （width, peak and stability） of the soliton are investigated. It is also found that the effects vary with the strengths of these interactions.
文摘Effects of the intergrain exchange interaction on magnetic properties of nanocomposite magnets were investigated by using the computer simulation based on the micromagnetic theory. The simulation was carried out under the assumptions that the strength of the intergrain exchange interaction is weaker than that of the intragrain exchange interaction, that inhomogeneous nanostructures result in the distribution of the strength of the intergrain exchange interaction, and that there exists nonmagnetic intergranular phase (NMIP) between grain boundaries. The distribution of the strength of the intergrain exchange interaction was simulated by the lognormal distribution with the standard deviation of σ.The calculations for Nd 2Fe 14B/α-Fe nanocomposite magnets reveal that a suitably weak intergrain exchange interaction and small grain size enable us to improve magnetic properties. It is also found that a Nd 2Fe 14B/α-Fe nanocomposite magnet has a potential of a (BH) max value exceeding 300 kJ·m -3. On the other hand, the calculations for Nd 2Fe 14B/Fe 3B nanocomposite magnets reveal that the distribution of the strength of the intergrain exchange interaction deteriorates magnetic properties significantly. Particularly, this tendency is remarkable, when the grain size L is larger than its optimum value, 11 nm. The existence of nonmagnetic boundary layers accelerats this tendency. At σ=0.2, the calculated demagnetization curve for the model magnet composed of Nd 2Fe 14B(36%)/Fe 3B(54%)/NMIP(10%) (Valume fraction) grains (L=15 nm) agrees with that obtained experimentally for a Nd 2Fe 14B/Fe 3B nanocomposite magnet. These results suggest importance of refinement of grain size, suppression of a nonmagnetic intergranular phase, and preparation of homogeneous nanostructure for superior magnetic properties.
基金financially supported by the National High-Tech Research and Development Program of China("863"Program)under Grant No.2002AA302603the National Natural Science Foundation of China under Grant Nos.50071062,59725103,and 50331030.
文摘Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co （and Fe65Co35） magnetic films was characterized by measuring static （mr（H）） and demagnetized （md（H）） remanence curves. According to conventional method： δm（H）=md（H） - [1 - 2mr（H）], the exchange interaction was evaluated. The switching fields H′p and Hp, at which static （mr（H）） and demagnetized （md（H）） remanence show the fastest change, were identified. The relative ratio η=Hp-H′p/Hp of switching fields H′p and Hp has a linear relationship with the maximum value δmmax of δm（H） curves, proposing an alternative way to characterize the exchange interaction.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11004005 and 60971019)the Young Scholars Fund of Beijing University of Chemical Technology,China(Grant No.QN0724)
文摘This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions （low temperatures and high magnetic fields） based on quantum theory. Here, five sets of crystal field parameters are discussed and compared. It demonstrates that, only considering the crystal field effect, the experiments can not be successfully explained. Thus, referring to the molecular field theory, an effective exchange field associated with the Dy-Dy exchange interaction is further taken into account. Under special consideration of crystal field and the exchange interaction field, it obtains an excellent agreement between the theoretical results and experiments, and further confirms that the exchange interaction field between rare-earth ions has great importance to magnetic properties in paramagnetic rare-earth gallium garnets.
基金the Natural Science Foundation of Inner Mongolia of China(Grant No.2019MS01021)the Research Program of Science and Technology at Universi-ties of Inner Mongolia Autonomous Region,China(Grant No.NJZY21454)the Theoretical Physics Discipline De-velopment and Communication Platform of Inner Mongolia University(Grant No.12147216).
文摘The dependences of spin wave resonance(SWR)frequency on the surface anisotropy field,interface exchange coupling,symmetry,biquadratic exchange(BQE)interaction,film thickness,and the external magnetic field in bilayer ferromagnetic films are theoretically analyzed by employing the linear spin wave approximation and Green’s function method.A remarkable increase of SWR frequency,except for energetically lower two modes,can be obtained in our model that takes the BQE interaction into account.Again,the effect of the external magnetic field on SWR frequency can be increased by increasing the biquadratic to interlayer exchange ratio.It has been identified that the BQE interaction is of utmost importance in improving the SWR frequency of the bilayer ferromagnetic films.In addition,for bilayer ferromagnetic films,the frequency gap between the energetically highest mode and lowest mode is found to increase by increasing the biquadratic to interlayer exchange ratio and film thickness and destroying the symmetry of the system.These results can be used to improve the understanding of magnetic properties in bilayer ferromagnetic films and thus may have prominent implications for future magnetic devices.
基金funded by National Natural Science Foundation of China,(Grant Nos.11974030 and 92165208)。
文摘Electron spins confined in semiconductor quantum dots(QDs)are one of potential candidates for physical implementation of scalable quantum information processing technologies.Tunnel coupling based inter exchange interaction between QDs is crucial in achieving single-qubit manipulation,two-qubit gate,quantum communication and quantum simulation.This review first provides a theoretical perspective that surveys a general framework,including the Helter−London approach,the Hund−Mulliken approach,and the Hubbard model,to describe the inter exchange interactions between semiconductor quantum dots.An electrical method to control the inter exchange interaction in a realistic device is proposed as well.Then the significant achievements of inter exchange interaction in manipulating single qubits,achieving two-qubit gates,performing quantum communication and quantum simulation are reviewed.The last part is a summary of this review.
文摘In present investigation exchange interactions of Pr_(n+1)Co_(3n+5)B_(2n)-type compounds have been evalu- ated in the light of molecular-field theory. The exchange interactions and ferromagnetism in these compounds are discussed in terms of lattice parameters and interatomic distance between Co atom.
基金Project supported by the National Natural Science Foundation of China(Grant No.11204026)the Fundamental Research Funds for Central Universities of the Ministry of Education of China(Grant No.n130405011)
文摘The dynamic properties of interacting vortex-antivortex pairs in thin film are studied by analytical calculations. An- alytical expressions for the magnetization vector distribution of vortex-antivortex pairs and the trivortex states are given. The magnetic states of the vortices are treated as having rigid structures, i.e., the vortex maintains its spin distribution when moving. The trajectories of the vortex cores are calculated by the Thiele＇s equation. It is found that the vortex-antivortex pair rotates around each other when they have opposite polarities, however, vortex and antivortex cores move along straight lines when they have the same polarity. The frequency of the rotation decreases with increasing the distance between the two cores of vortex-antivortex pair, and it has a lower value when a third vortex is introduced.
基金This work has been supported by the projects No.59725103 and 59871054 of the National Natural Sciences Foundation of China and by the Science and Technology Commnission of Shenyang and Liaoning.Z.J.Guo as aiso indebted to Prof.A.S.Miarkosyan(Russia)for helpful discussions.
文摘Structure, magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investigated by means of X-ray diffraction, a.c. initial susceptibility, extracting sample magnetometer, Mossbauer spec-troscopy and standard strain gauge techniques. The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration, deviating from the Vegard's law. Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0. The saturation magnetization Ms at temperatures 1.5 K, 77 K and 300 K have the same variation tendency as the composition dependence of Curie temperature, in consistence with rigid-band model. The easy magnetization direction (EMD) of Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x<0.6, and changes to [110] for x=0.8, while Sm0.9Pr0.1Co2 stays in the paramagnetic state at room temperature. The composition dependence of the average hyperfine field,Hhf , demonstrates a similar variation tendency as that of the saturation magnetization Ms and Curie temperature Tc. The spontaneous magnetostricton Am increases with increasing Co content. The saturation magnetostriction λs decreases monotonically with increasing x, which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of Am. A two-sublattice model has been proposed to understand the intermediate region between the [111] and [110] spin configurations, which can also be used to explain the temperature dependence of magnetization.
文摘SmCo/FeCo/SmCo trilayer was deposited with two different thickness configurations for soft phase (FeCo);50 nm/10 nm/50 nm and 50 nm/25 nm/50 nm were deposited on Si (111) substrate and Ta (50 nm) seed layer by RF magnetron sputtering in a pressure, p, of 30 - 35 m Torr. After deposition the films were annealed under Ar atmosphere at temperature T equal to 923 and 973 for different times followed by quenching in water. X-ray diffraction patterns were obtained to identified phase presents and calculate average crystallite size. To study the effect of configuration thickness in soft phases, DC magnetic measurements were carried out;the measurements were done in the temperature interval of 300 - 50 K. Hysteresis loops collected at low temperatures exposed an increment in coercivity with the decrease of T and at same time, presented a “knee” in the second quadrant of the demagnetization curve, which suggests that the inter-layer exchange coupling becomes less effective, being more evident for sample with 50 nm/25 nm/50 nm thickness. Moreover, δM (H) plots were calculated from magnetic measurements at three different temperatures, T, equal to 300, 150 and 50 K, which corroborates that the dipolar interactions became stronger when thickness of soft phases increases. Finally, the thickness effect is attributed to the SmCo5 phase magnetocrystalline anisotropy constant, which is responsible for the exchange coupling length.
文摘Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coefficient B20 and the magnetic exchange interaction was studied as temperature approaches to 0 K. The results show that the stabilization energy contributed by Tb3+ is linear with crystal field coefficient B20 approximately, but it is insensitive to the change of magnetic exchange interaction for the strong magnetic substances such as TbCo5, Tb2Co17 and Tb2Fe14B compounds.
基金We thank DST and SERB(SB/SJF/2019-20/12,CRG/2022/001697)for fundingAS thanks UGC/CSIR for the fellowship+1 种基金the financial support from the Prime Ministers Research Fellowship(PMRF)the Australian Research Council(DP110100525)for a Discovery grant.
文摘A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found to display single-molecule magnetism(SMM)behaviour with a Ueff=54 cm^(−1)and well-resolved magnetisation hysteresis plots,with a blocking temperature,T_(B)=3.5 K.In the present study,fourteen related{Cr^(Ⅲ)2 Dy^(Ⅲ)_(2)}complexes have been synthesised,and their magnetic properties have been studied.The study probes how chemical changes in bridging ligands and coordination environment affect the SMM properties compared to the parent complex.We show that by making simple chemical modifications to the ligands,the Ueff and T_(B)values change,with Ueff values ranging from 22 to 65 cm^(−1)and T_(B)1.8 K to 4.7 K.We also show that SMM behaviour can be turned off by manipulation of the coordination sphere around the Dy^(Ⅲ)ion.Based on these experimental results,we undertook a detailed theoretical study to understand why these changes occur.The theoretical studies further describe the mode of exchange mechanism in such complexes and how it controls the blocking temperature.Further,we have found that the exchange coupling between the Dy^(Ⅲ)–Cr^(Ⅲ)ions strongly influences the magnetic relaxation for this family of complexes,and interestingly,the exchange between the Cr^(Ⅲ)–Cr^(Ⅲ)centres plays a determining role in the overall SMM properties,which has been ignored in previous studies.We have derived a relation between the magnetic exchange and T_(B)for such 3d–4f SMMs where exchange coupled states play a dominant role,revealing the blocking temperature is strongly correlated to the overall magnetic exchange.This clearly illustrates the importance of inducing strong exchange coupling to enhance not only the magnetisation reversal barrier but also T_(B)via quenching of zero-field quantum tunnelling of the magnetisation(QTM)in{3d–4f}type complexes.
基金supported by the Taishan Scholar Program,Qingdao Natural Science Foundation(25-1-1-168-zyyd-jch)111 Project of China(D20017).
文摘The performance of Single-Molecule Magnets(SMMs)can be enhanced by reducing quantum tunneling of magnetization(QTM),which can be achieved with the aid of strong magnetic exchange interactions and strong magnetic anisotropy.When 4d ions are mixed with 4f ions,the strong spin–orbit coupling and moderate ligand-field strength of 4d elements complement the highly anisotropic 4f ions,and the combined effect decreases the transverse anisotropy and stabilizes the magnetic easy axis,both of which are essential for lowering QTM.Despite their synthetic challenges,the unique electronic properties of 4d–4f systems make them promising candidates for designing advanced single-molecule magnets.Here,we report the synthesis,magnetic,and theoretical studies of five tetranuclear“butterfly-shaped”complexes of formulae[Ru^(Ⅲ)_(2)Ln^(Ⅲ)_(2)(OMe)_(2)(o-tol)_(4)(mdea)_(2)(NO_(3))_(2)](Ln=Gd(1-Gd),Tb(2-Tb),Dy(3-Dy),Ho(4-Ho),mdeaH2=N-methyldiethanolamine)and[Ru^(Ⅲ)_(2)Er^(Ⅲ)_(2)(OMe)_(2)(o-tol)6(mdea)_(2)]·2MeOH(5-Er).Complexes 2-Tb,4-Ho,and 5-Er are the first reported examples of Ru-4f complexes using these Ln^(Ⅲ)ions.DC magnetic susceptibility studies revealed an antiferromagnetic exchange interaction between the Ln^(Ⅲ)and Ru^(Ⅲ)metal ions in all complexes.Among the complexes reported,3-Dy and 4-Ho show out-of-phase susceptibility signals in the absence of an external magnetic field,while the remaining complexes exhibit field-induced slow relaxation of magnetization.These observations were attributed to the presence of an ideal crystal field combined with the strong exchange interaction exerted between the Ru^(Ⅲ)and Ln^(Ⅲ)ions in the complexes.Importantly,the 4-Ho is the first non-dysprosium Ru–Ln polynuclear complex to show zero-field SMM behavior.Detailed ab initio CASSCF+RASSI-SO+SINGLE_ANISO+POLY_ANISO and Density Functional Theory(DFT)calculations reveal that the magnitude of exchange interaction increases in the following order:1-Gd(−1.3 cm^(−1))<2-Tb(−1.8 cm^(−1))<3-Dy(−2.7 cm^(−1))<4-Ho(−2.8 cm^(−1))<5-Er(−4.0 cm^(−1)).The larger single-ion anisotropy of the DyⅢions in 3-Dy leads to the largest barrier of 101.8 cm^(−1)(146 K),which increases further to 111 cm^(−1)(158.7 K)when considering the exchange-coupled model,with the strong Ru⋯Ln exchange further quenching QTM effects.These results highlight the importance of strong magnetic exchange between 4d–4f(Ru^(Ⅲ)⋯Ln^(Ⅲ))ions in enhancing the SMM behavior of 4d–4f complexes.
基金the Summer Student Program at HZB for the opportunity to conduct THz-EPR measurementsFinancial support by the Russian Science Foundation through grant no.22-13-00376(X-and Q-band EPR measurements)is acknowledged+1 种基金the financial support from the institutional sources of the Department of Inorganic Chemistry,Palacký University Olomouc,Czech Republicindebted to Deutsche Forschungsgemeinschaft(DFG,German Research Foundation,Project No.LO 2898/1-1).
文摘Single-ion magnets(SIMs)are the most promising candidates for magnetic storage and processing of information at the molecular level.Apart from the properties of each isolated SIM,their performance crucially depends on intermolecular exchange interactions in bulk materials or those occurring when individual SIMs are assembled into arrays for practical applications.However,compared with their magnetic anisotropy,the correlation of in-bulk intermolecular exchange interactions and magnetic relaxation parameters has been established to a much lesser extent.In this work,using an extended protocol involving XRD,multifrequency and frequency-domain EPR,SQUID magnetometry,DFT and ab initio calculations,we investigated intermolecular interactions in a new series of four bis-(phenoxy Schiff base)Co(Ⅱ)complexes representing field-induced SIMs.Combined multifrequency EPR ranging from 9 GHz to>1 THz allowed unique measurement of weak intermolecular exchange couplings of the order of 0.01 cm^(-1).Consolidation of EPR data with ac/dc SQUID magnetometry and detailed structural and quantum-chemical analyses allowed us to reliably analyze the key performance characteristics of these SIMs,the degree of polyhedral distortion,and the values of intermolecular exchange couplings in an attempt to achieve a firm interplay among them.Such analysis can become prototypical for future design and evaluation of crystals,assemblies and arrays of SIMs.
基金The University of Manchester and EPSRC EPR National Research Facility(NS/A000055/1)the EPR spectrometers and SQUID magnetometer,and the EPSRC for funding an X-ray diffractometer(grant number EP/K039547/1).+3 种基金The University of Manchester for a Presidential Fellowship,The Royal Society for a University Research Fellowship,and the European Research Council for a Starting Grant(ERC-2019-STG-851504)R.E.P.W.thanks the EPSRC for an Established Career Fellowship(EP/R011079/1)the European Research Council for an Advanced Grant(ERC-2017-ADG-786734)the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(grant agreements no.786734 and 851504).
文摘We report the synthesis and characterization of two symmetric homo-dimetallic lanthanide complexes based on methyl-substituted 8-hydroxyquinoline(HMeQ).The aryloxo-bridged core gives rise to weak magnetic coupling between pairs of ErⅢand YbⅢions,as revealed by magnetic and EPR spectroscopy studies.EPR measurements of magnetically dilute species,coupled with CASSCF-SO calculations,allows modelling of the EPR spectra of the exchange coupled species and the magnetic data simultaneously.This work adds to the database of exchange coupled{Ln}_(2)molecules which have been thoroughly characterised by EPR spectroscopy and modelled using an S_(eff)=1/2 approach to describe the interaction of ground Kramers states,and highlights the differences between centro-symmetric and asymmetric dimetallics.
文摘The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.
基金supported by the Beijing Natural Science Foundation(Grant No.2214070)Science Center of the National Science Foundation of China(Grant No.52088101)+6 种基金National Natural Science Foundation of China(Grant Nos.52001012,51901057,U1832219,51771223,and 51971240)Heye Chongming Project(Grant No.HYCMP-2021001)National Key Research and Development Program of China(Grant Nos.2021YFB3501202,2021YFB35015043,2020YFA0711502,2019YFA0704900,2018YFA0305704,and 2017YFA0303601)Key Projects of Capacity Construction of Science and Technology Innovation Service(Grant No.19002020124)Beijing Talent Training Quality Construction Project(Grant No.19008021064)Strategic Priority Research Program B(Grant No.XDB33030200)Key Program of the Chinese Academy of Sciences(CAS)。
文摘The 2:14:1-type rare-earth(RE)-Fe-B permanent magnets prepared by the dual alloy method have been found to possess much superior magnetic properties to those prepared by the single alloy method,providing an appealing route to promote the utilization of high-abundance RE elements Ce and La and balance the use of the RE source.However,the relationship between magnetic interactions among different 2:14:1 main phases and superior magnetic properties is still unclear.In this study,we investigated the magnetic interactions and reversal field distribution in these magnets using first-order reversal curve(FORC)images.The FORC images showed that(Nd,Pr)27.8(La,Ce)2.7FebalM1.4B1.0(S-9)and(Nd,Pr)19.5(La,Ce)11.0FebalM1.4B1.0(S-36)have the characteristics of multiple main phases.The reverse magnetic fields corresponding to the soft and hard main phases,as well as the associated exchange coupling,were highly dependent on the La Ce content.The higher the La Ce content,the weaker the exchange coupling and the more asynchronous the demagnetization process.In addition,the FORC images indicated that the magnetization reversal process also varies with La Ce content,where the nucleation and propagation of reversed domains dominant in the S-9 magnet,while the domain propagation in the S-36 magnet is considerably suppressed.Additional micromagnetic simulations also revealed that the coercivity and exchange coupling of multi-main-phase magnets decrease with increasing La Ce content,correlating well with the experimental results.These findings may not only contribute to a better understanding of the complex magnetic interactions between the soft and hard phases and how they affect macroscopic magnetic properties but also help in improving the magnetic performance of the RE-Fe-B magnets with high La Ce content.
文摘A novel heterospin complex {[(CuL)Ni(IM 2Py) 2](ClO 4) 2} 2·2H 2O (L=2,3 dioxo 5,6:14,15 dibenzo 1,4,8,12 tetraazacyclo pentadeca 7,12 diene, IM 2Py=2 (2′ pyridyl) 4,4,5,5 tetra^methyl 4,5 dihydro 1 H imidazoline 1 oxyl) has been synthesized and its crystal structure was determined by X ray diffraction analysis. In order to interpret the exchange interaction of this asymmetric heterospin system, a theoretical model has been established. Using this theoretical model the magnetic susceptibility data have been fitted and lead to coupling constant values equal to 1 4 cm -1 (Ni Rad) and -38 0 cm -1 (Ni Cu), respectively.
基金This work was financially supported by the National Natural Science Foundation of China (No.10074005)
文摘The influence of annealing time on the magnetic properties and microstructure of nanocomposite Pr7.5Dy1Fe71Co15Nb1B4.5 ribbons was systematically investigated by the methods of vibrating sample magnetometer （VSM）, X-ray diffraction （XRD） and high resolution transmission electron microscopy （HRTEM）. Interaction domains derived from strong exchange coupling interactions between hard and soft magnetic grains were imaged using magnetic force microscopy （MFM）. Maximum remanence, intrinsic coercivity, and maximum energy product values were obtained in the ribbons annealed at 700℃ for 15 min, which were composed of Pr2（Fe, Co）14B, α-（Fe, Co）, and slight Pr2（Fe, CO）17 phases. Although Jr, Hci, and （Bn）max decreased gradually with further increase of annealing time, it is emphasized that comparatively high Jr and Hci and （BH）max were obtained in a wide annealing time period of 15 to 360 min. The shape of initial magnetization curves and hysteresis loops change as a function of annealing time, indicating different magnetization reversal routes, which can be fully explained by the corresponding microstructure.
