Ferrimagnetic materials exhibiting remanence can be used to achieve unidirectional electromagnetic-field propagation in the form of magnetoplasmons(MPs)in the subwavelength regime.This study investigates the MP proper...Ferrimagnetic materials exhibiting remanence can be used to achieve unidirectional electromagnetic-field propagation in the form of magnetoplasmons(MPs)in the subwavelength regime.This study investigates the MP properties and various guiding modes in a hollow cylindrical waveguide made of materials that exhibit remanence.Pattern analysis and numerical simulations are used to demonstrate that dispersion relationships and electromagnetic-field distribution are strongly affected by the operating frequency and physical dimensions of the structure.In addition,the existence of two different guiding modes is proved,namely regular and surface-wave modes.By adjusting the operating frequency and reducing the diameter of the hollow cylinder,the regular mode can be suppressed so as to only retain the surface-wave mode,which enables unidirectional MP propagation in the cylindrical waveguide.Moreover,the unidirectional surface-wave mode is robust to backscattering due to surface roughness and defects,which makes it very useful for application in field-enhancement devices.展开更多
SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization ...SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film,both the coercivity(Hc)and remanence(Mr)of films are difficult to enhance simultaneously.In this paper,SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process.The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed.By adjusting the Sm/Co atomic ratio from 1:5 to 1:4,Co soft magnetic phase disappears and the single phase SmCo5 is obtained,leading to the increase of coercivity of the films from 30 to 34 kOe.The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated.When the deposition temperature increases from room temperature to 250℃,the coercivity will further increase from 34 to 51 kOe.However,a severe kink is observed in the demagnetization curves due to the poor exchanged coupling.An analysis of transmission electron microscopy(TEM)confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5,which contributes to the decoupling and low remanence ratio.Therefore,doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films.Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced.We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization,which can be utilized in high performed MEMS devices.展开更多
As an effective strategy to improve the properties of electrocatalysts,magnetic field-assisted electrocatalytic water splitting has attracted increasing attention recently.However,the corresponding enhancements mostly...As an effective strategy to improve the properties of electrocatalysts,magnetic field-assisted electrocatalytic water splitting has attracted increasing attention recently.However,the corresponding enhancements mostly depend on the exertion of an external magnetic field during electrochemical reactions,which results in a high cost of industrial production,and makes the magnetic field manipulation of electrocatalysis become a challenging task.In this work,instead of the external magnetic field,a bias magnetic field is self-supplied by the remanence state of a ferromagnetic electrocatalyst of FePt.Owing to the assistance of this bias magnetic field,the FePt film in the remanence state shows the overpotential of 229 mV during hydrogen evolution reaction,which is much lower than that in its demagnetization state(283 mV).Our findings demonstrate that the remanence in ferromagnetic electrocatalysts can improve the catalytic performance,which is attributed to the decrease in domain walls.展开更多
It is still a challenge to simultaneously enhance coercivity(H_(cj))and remanence(J_(r))of hot-deformed Nd-Fe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance between H_(cj)and ...It is still a challenge to simultaneously enhance coercivity(H_(cj))and remanence(J_(r))of hot-deformed Nd-Fe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance between H_(cj)and Jr by flake Cu powder assisted DyF_(3)interflake addition.The Hcj increases from 1218 to 1496 kA/m and Jr increases from 1.32 to 1.34 T compared with the original magnet.Results show that the width of coarse grain layers reduces because of the introduction of flake Cu,which increases the contact areas of the adjacent grains at ribbon interfaces and suppresses the excessive growth of grains.The stronger degree of texture and higher density compared with the original magnet should take the responsibility for the increase of J_(r).Additionally,the aggregation regions of rare earth rich(RE-rich)phase reduce and the betterment of the microstructure is another reason for the enhancement of Jr in the flake Cu aided DyF_(3)hot-deformed magnet.This strategy of using flake powder additives provides a promising method for optimizing microstructure and enhancing magnetic properties of hot-deformed Nd-Fe-B magnets.展开更多
Er-doped Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)magnets with a low remanence temperature coefficient were prepared by powder metallurgy method.The influence of Er content on the remanence and microstruct...Er-doped Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)magnets with a low remanence temperature coefficient were prepared by powder metallurgy method.The influence of Er content on the remanence and microstructure was investigated.X-ray diffractometer(XRD)analysis showed that the magnets with different Er contents consist of 2:17 R phase and 1:5 H phase.Scanning electron microscopy(SEM)analysis showed that the composition of the matrix is consistent with stoichiometric composition and no obvious precipitated phase appears.With the increase in doped Er amount,the temperature stability of Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)is getting better.When x is up to 0.3,the magnets with a low remanence temperature coefficient are obtained and the remanence descends tardily from 0.86 to 0.80 T as the temperature rises from room temperature to 400℃.These results indicate that Er substitution for Sm in SmCobased permanent magnets together with optimal composition and proper heat treatment could achieve a desired magnetic performance combined with high thermal stability.展开更多
The relation between microscopic properties (e.g., layer thickness, easy axis orientation) and the macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system is investigated ...The relation between microscopic properties (e.g., layer thickness, easy axis orientation) and the macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system is investigated based on a simple micromagnet approach. We concentrate on a multilayer design with periodic boundary condition, where alternating soft/hard layers build a nanostructured multilayer. For any easy axis direction in the soft and hard layers a simple explicit expression of remanence of the system has been derived analytically. We find that the remanence clearly depends on the thickness of the soft magnetic layer and is nearly independent of the thickness of hard magnetic layer. On the other hand, the remanence increases upon reducing the angle enclosed by the saturation magnetization and the easy axis directions of soft magnetic layer. However, it is unsensitive to the easy axis direction of hard magnetic layer, but there exists a maximum remanence for a certain easy axis direction of hard magnetic layer.展开更多
There are some abnormal phenomena in the test or operation of transformer, which are mainly caused by the residual magnetism in the core. Therefore, this paper briefly introduces the electromagnetic characteristics of...There are some abnormal phenomena in the test or operation of transformer, which are mainly caused by the residual magnetism in the core. Therefore, this paper briefly introduces the electromagnetic characteristics of ferromagnetic elements, and analyzes the mechanism of transformer remanence based on the electromagnetic characteristics. Finally, the influence of transformer remanence on transformer current, relay protection device, primary equipment and power quality is studied, and the corresponding preventive measures are put forward.展开更多
The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic...The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic field polarity reversals,the oceanic lithosphere has significant remanent magnetization,which causes magnetic anomaly stripes parallel to the mid-ocean ridges.However,it is difficult to construct a high-resolution lithospheric magnetic field model in oceanic regions with relatively sparse data or no data.Using forward calculated lithospheric magnetic field data based on an oceanic remanent magnetization(ORM) model with physical and geological foundations as a supplement is a feasible approach.We first collect the latest available oceanic crust age grid,plate motion model,geomagnetic polarity timescale,and oceanic lithosphere thermal structure.Combining the assumptions that the paleo geomagnetic field is a geocentric axial dipole field and that the normal oceanic crust moves only in the horizontal direction,we construct a vertically integrated ORM model of the normal oceanic crust with a known age,including the intensity,inclination,and declination.Both the ORM model and the global induced magnetization(GIM) model are then scaled from two aspects between their forward calculated results and the lithospheric magnetic field model LCS-1.One aspect is the difference in their spherical harmonic power spectra,and the other is the misfit between the grid data over the oceans.We last compare the forward calculated lithospheric magnetic anomaly from the scaled ORM and GIM models with the Macao Science Satellite-1(MSS-1) observed data.The comparison results show that the magnetic anomalies over the normal oceanic crust regions at satellite altitude are mainly contributed by the high-intensity remanent magnetization corresponding to the Cretaceous magnetic quiet period.In these regions,the predicted and observed anomalies show good consistency in spatial distribution,whereas their amplitude differences vary across regions.This result suggests that regional ORM construction should be attempted in future work to address these amplitude discrepancies.展开更多
This paper presents a security strategy for resisting a physical attack utilizing data remanence in powered- off static random access memory （SRAM）. Based on the mechanism of physical attack to data remanence, the s...This paper presents a security strategy for resisting a physical attack utilizing data remanence in powered- off static random access memory （SRAM）. Based on the mechanism of physical attack to data remanence, the strategy intends to erase data remanence in memory cells once the power supply is removed, which disturbs attackers trying to steal the right information. Novel on-chip secure circuits including secure power supply and erase transistor are integrated into conventional SRAM to realize erase operation. Implemented in 0.25μm Huahong-NEC CMOS technology, an SRAM exploiting the proposed security strategy shows the erase operation is accomplished within 0.2 μs and data remanence is successfully eliminated. Compared with conventional SRAM, the retentive time of data remanence is reduced by 82% while the operation power consumption only increases by 7%.展开更多
Previous palaeomagnetic work shows that the mechanism of remanence acquisition on sediments is very complicated. Different magnetizing processes under different conditions may produce some anomalous magnetic signals w...Previous palaeomagnetic work shows that the mechanism of remanence acquisition on sediments is very complicated. Different magnetizing processes under different conditions may produce some anomalous magnetic signals which have nothing to do with the changes of the geomagnetic field and are difficult to explain.;The depositional remanent magnetization (DRM) may produce an inclination error and a bedding error, while postdepositional remanent magnetization (PDRM) may result in a time delay between the magnetic and sedimentary ages. When there are some different magnetic phases with different lock-in depths in the sediments, it is difficult to judge the depth of the reversal or excursion, or even the artificial magnetic signal may be produced. Even if there is only one magnetic phase in the sediment, the recorded magnetic signals may also be different if the lock-in depth is changed comparative to the lasting period of one reversal or excursion. Demagnetization may also change the primary magnetic records and the changes of water content may result in the displacement of magnetic boundary. The so-called "unstable core", representing subtle changes in mineralogy into and out of a self-reversal region or a viscous magnetization region, gives a complicated palaeomagnetic record with many apparent changes in the palaeomagnetic direction. Moreover, some physical disturbances, such as biodisturbance, deformation, drilling processes and drying effects, may result in the remanence alteration. Some palaeomagnetic investigations demonstrate that good magnetic signals are invariably achieved on homogenous mud or clay sediments, but the worse signals on inhomogeneous profiles, especially on sandy layers.展开更多
The melt-spun ribbons of nominal composition Pr_(9)Fe_(84.2-x)B_(6.2)P_(0.3)Zr_(0.3)Cu_(x)(x=0,0.5,1,2)were prepared at wheel speeds of 21 m·s^(-1),27 m·s^(-1),30 m·s^(-1),and 33 m·s^(-1).The XRD p...The melt-spun ribbons of nominal composition Pr_(9)Fe_(84.2-x)B_(6.2)P_(0.3)Zr_(0.3)Cu_(x)(x=0,0.5,1,2)were prepared at wheel speeds of 21 m·s^(-1),27 m·s^(-1),30 m·s^(-1),and 33 m·s^(-1).The XRD patterns show that as the wheel speed increases,the crystallinity of the 2:14:1 hard phase decreases,while that of theα-Fe soft phase increases.The(BH)_(max),remanence,and coercivity are improved from 63 kJ·m^(-3),0.85 T,and 515 kA·m^(-1)for the Cu-free ribbons to 171 kJ·m^(-3),1.08 T,and684 kA·m^(-1)with x=0.5.The high squareness ratio of J_(r)/J_(s)~0.82 at 0.5 at.%Cu(27 m·s^(-1))indicates strong exchange coupling due to small grain sizes of 15 nm and 30 nm for soft and hard magnetic phases,respectively.The SEM images revealed smooth morphology and uniform element distribution at 0.5 at.%Cu(27 m·s^(-1)),contributing to the high magnetic properties.The low recoil permeability(μrec)value of 5.466×10^(-4)T/kA·m^(-1)to 1.970×10^(-4)T/kA·m^(-1)confirms the strong exchange coupling with x=0.5(27m·s^(-1)).The initial magnetization curves show that the coercivity mechanism of the Cu-free alloy evolves from the nucleation of the reverse domain to the domain wall pinning as the wheel speed increases,resulting in a high coercivity value of 818 kA·m^(-1)(33 m·s^(-1)).Conversely,for the Cu-added alloy,the coercivity mechanism changes from pinning to the nucleation of the reverse domain from low to high wheel speed.展开更多
A novel Nd-Fe-B type permanent magnet with excellent thermal stability was designed by Co replacing Fe in the main phase and the grain boundary phase.The remanence and coercivity temperature coefficient reach 0.058%/...A novel Nd-Fe-B type permanent magnet with excellent thermal stability was designed by Co replacing Fe in the main phase and the grain boundary phase.The remanence and coercivity temperature coefficient reach 0.058%/℃and 0.465%/℃in the te mperature range from 25 to 100℃,which are much lower than those of commercial Nd-Fe-B magnet.An enhanced Curie temperature is obtained for the novel magnet due to the Co substitution,which significantly improves the operating temperature.The microstructure result reveals that an amorphous phase exists in the intergranular grains which is probably responsible for the deterioration of intrinsic coercivity.This work can provide a reference for the design and optimization of components of sintered Nd-Fe-B magnets with excellent thermal stability.展开更多
Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)S...Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)Sr_(0.4)Ce_(x)Fe_(2-x)O_(4). Following that,a comprehensive X-ray diffraction analysis unveiled the crystalline cubic structure of the synthesized materials.Through the utilization of the M-H loop approach,the ferromagnetic attributes of ferrites were assessed,and the assimilation of rare earth elements led to substantial enhancements in saturation magnetization,remanence,and coercivity.Spinel ferrites with a high concentration of rare earth elements have improved direct current resistivity and activation energy.The logarithm of a material's resistance increased from 5.29 to 8.12 Ω·cm as cerium is added.With a change in the amount of cerium,the activation energy goes up from 0.19 to 0.29.By changing the frequency from 5.5 to 9.5 GHz,the dielectric characteristics were determined.As the frequency goes up,the dielectric constant goes down.Spinel ferrites that have been made better in every way can be used in high-frequency applications.展开更多
The orientation of stable single domain (SSD) ferrimagnetic particles in an igneous rock sample was determined by a sensitive technique utilizing gyroremanent magnetization (GRM). Components of GRM were measured in th...The orientation of stable single domain (SSD) ferrimagnetic particles in an igneous rock sample was determined by a sensitive technique utilizing gyroremanent magnetization (GRM). Components of GRM were measured in the sample upon exposure to an alternating field (AF) at various orientations in 3 orthogonal planes. The major components of GRM exhibited a sin(2θ) dependence on AF orientation in the respective perpendicular planes. This was in accordance with theory [1] and contrary to some previously reported experimental results on magnetic recording tape, which produced a distorted sin(2θ) dependence of the GRM [1]. The explanation is likely due to the SSD ferrimagnetic particles in the rock sample being more dispersed (less interacting) compared to the highly interacting SSD particles in the magnetic tape sample of the previous study. The GRM results were consistent with another remanence anisotropy method, anisotropy of isothermal remanent magnetization (AIRM). This method again measures the anisotropy of the remanence carrying ferrimagnetic particles, but the IRM is also acquired by larger multidomain (MD) particles as well as by the SSD particles. The results were also consistent with the visible rock anisotropy (petrofabric), the anisotropy of magnetic susceptibility (AMS), and the shear wave velocity anisotropy. A comparison of all the methods demonstrated that the fine SSD particles, which make up only a small proportion of the rock, were aligned in quite a similar orientation to that of the main rock forming minerals that constituted the bulk of the sample.展开更多
The variations of intrinsic coercivity and remanence of sintered Nd-Fe-B magnets with ultra-high intrinsic coercivity were investigated. The results showed that the intrinsic coercivity and remanence declined simultan...The variations of intrinsic coercivity and remanence of sintered Nd-Fe-B magnets with ultra-high intrinsic coercivity were investigated. The results showed that the intrinsic coercivity and remanence declined simultaneously with increasing temperature, but the squareness of the magnets has hardly been changed. The temperature coefficients of remanence （α） and coercivity （β） for the magnets were calculated by two different methods, and the variations of the temperature coefficients and the microstructure of sintered Nd-Fe-B magnets were analyzed. The temperature coefficients of remanence （α） and coercivity （β） for the sintered magnets are very small, and the existence of fine microstructure is necessary to obtain sintered Nd-Fe-B magnets with ultra-high intrinsic coercivity.展开更多
The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC ...The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coereivity of the FePt based alloy as a function of the Nd content had maximum values, respectively.展开更多
Anisotropic CeCo4.325_xCuo.675Fex （x ： 0.475- 0.875） sintered magnets were prepared by traditional powder metallurgical method. Influence of ball-nfilling time and iron content on microstructure and magnetic proper...Anisotropic CeCo4.325_xCuo.675Fex （x ： 0.475- 0.875） sintered magnets were prepared by traditional powder metallurgical method. Influence of ball-nfilling time and iron content on microstructure and magnetic properties of the CeCo4,325-xCuo.675Fex sintered magnets were investigated. It is shown that the properties of the magnet produced by mag- netic powders ball-milled for 40 min are better than that for 30 rain. With iron content increasing, remanence Br and maxi- mum energy product （BH）m increase first and then decrease. The optimal magnetic properties are obtained for the CeCo3.65Cuo.675Feo.675 sintered magnet： Br=0.685 T, the intrinsic coercivity Hci = 350 kA.m-1, and （BH）m ： 85.6 kJ.m-3. The increase of Br is mainly influenced by iron content of 1：5 matrix which can properly increase the saturation induction Bs; the rapid increase of the amount of Ce-rich phase and 5：19 phase gives rise to the deterioration of the magnets when x ≥ 0.775.展开更多
Nanocrystalline Fe-based alloys offer a new opportunity for tailoring soft magnetic materials. Nanocrystalline alloy in the form of ribbon with the composition of Fe73.5Cu1Nb3Si13.5B9 was prepared by rapid quenching m...Nanocrystalline Fe-based alloys offer a new opportunity for tailoring soft magnetic materials. Nanocrystalline alloy in the form of ribbon with the composition of Fe73.5Cu1Nb3Si13.5B9 was prepared by rapid quenching method for soft magnetic properties analysis. The rapidly quenched alloy has been annealed in a controlled way in the temperature range 490℃ to 680℃ and annealing time 1 min to 60 min. The study of the structural parameters has been investigated by means of XRD analysis. Magnetic properties were analyzed by measuring B-H loop and frequency dependence of initial permeability. Enhanced value of initial permeability by two orders of magnitude and very low value of relative loss factor of the order of 10–3 has been observed with the variation of annealing temperature and time. The initial permeability for the optimum annealed sample has been found 23,064 as compared with 360 for its amorphous counterpart. The initial permeability spectra show dispersion around 100 kHz. Magnetic hysteresis has been investigated by measuring B-H loops at various magnetic fields for different annealing temperature and time. The coercivity and remanence has been found to decrease significantly for optimized annealed condition compared to as-cast state. The core loss of the samples decreases with the annealing time which indicates the good magnetic property of soft magnetic materials.展开更多
In order to improve and stabilize the magnetic properties of nanocomposite Nd2Fe14B/α-Fe magnetic alloys by a compositional adjustment, small amount of Dy and/or Co was added to Nd9Fe84B7 alloys. DTA analysis on the ...In order to improve and stabilize the magnetic properties of nanocomposite Nd2Fe14B/α-Fe magnetic alloys by a compositional adjustment, small amount of Dy and/or Co was added to Nd9Fe84B7 alloys. DTA analysis on the amorphous of the alloys took place as the soft magnetic phases were crystallized, and then the hard magnetic Nd2Fe14B was precipitated from them. While α-Fe and a metastable 1:7 (TbCu7-type) phase were formed simultaneously in Dy and Co-free alloys, they were crystallized separately at different temperatures after Dy or Co was added. This phase separation occurred more clearly in the Dy-treated alloys and the other soft magnetic phase Fe3B was also stabilized by Dy and/or Co. The 1: 7 phase that was stabilized by Dy and/or Co was not eliminated at 700 ℃, decreasing magnetic properties of the alloys. It was eventually disappeared above 725 ℃, but Fe3B was not eliminated even at 750 ℃ when Dy was added more than 0.5 at% or Co was added more than 2.0 at%. Amount of Nd2Fe14B in the alloys tended to increase as Dy addition increased,whereas Co addition did not lead to any appreciable change in the ratio of α-Fe and Nd2Fe14B. Moreover, Dy addition apparently increased coercivity of an alloy while Co addition had a beneficial effect on remanence. The grains in the Dytreated alloys were usually finer than those in the Co-treated alloys. The grain size of both α-Fe and Nd2Fe14B in the alloys exhibiting mr ≥ 0.72 was in the range of 20 ～ 40 nm or even larger 50 nm, which is larger than the theoretical optimum size ( ～ 10 nm). Typical magnetic properties obtained from a Nd7.5Dy1.5Fe82.5Co1.5B7 alloy annealed for 12 min at 725 ℃were iHc=4.85 kOe, Br= 11.32 kG, (BH)max = 15.73 MGOe, and mr=0.73.展开更多
文摘Ferrimagnetic materials exhibiting remanence can be used to achieve unidirectional electromagnetic-field propagation in the form of magnetoplasmons(MPs)in the subwavelength regime.This study investigates the MP properties and various guiding modes in a hollow cylindrical waveguide made of materials that exhibit remanence.Pattern analysis and numerical simulations are used to demonstrate that dispersion relationships and electromagnetic-field distribution are strongly affected by the operating frequency and physical dimensions of the structure.In addition,the existence of two different guiding modes is proved,namely regular and surface-wave modes.By adjusting the operating frequency and reducing the diameter of the hollow cylinder,the regular mode can be suppressed so as to only retain the surface-wave mode,which enables unidirectional MP propagation in the cylindrical waveguide.Moreover,the unidirectional surface-wave mode is robust to backscattering due to surface roughness and defects,which makes it very useful for application in field-enhancement devices.
基金Project supported by the National Key R&D Program of China(2022YFB3505700,2022YFB3807900)National Natural Science Foundation of China(51901079)+2 种基金R&D(Research and Development)Plan in Key Areas of Guangdong Province(SDZX2021002,212021032611700001)Natural Science Foundation of Guangdong Province(2020A1515010736,2021A1515010451)the Guangzhou Municipal Science and Technology Program(202007020008)。
文摘SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system(MEMS).However,due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film,both the coercivity(Hc)and remanence(Mr)of films are difficult to enhance simultaneously.In this paper,SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process.The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed.By adjusting the Sm/Co atomic ratio from 1:5 to 1:4,Co soft magnetic phase disappears and the single phase SmCo5 is obtained,leading to the increase of coercivity of the films from 30 to 34 kOe.The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated.When the deposition temperature increases from room temperature to 250℃,the coercivity will further increase from 34 to 51 kOe.However,a severe kink is observed in the demagnetization curves due to the poor exchanged coupling.An analysis of transmission electron microscopy(TEM)confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5,which contributes to the decoupling and low remanence ratio.Therefore,doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films.Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced.We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization,which can be utilized in high performed MEMS devices.
基金financially supported by the National Natural Science Foundation of China(No.52101215)。
文摘As an effective strategy to improve the properties of electrocatalysts,magnetic field-assisted electrocatalytic water splitting has attracted increasing attention recently.However,the corresponding enhancements mostly depend on the exertion of an external magnetic field during electrochemical reactions,which results in a high cost of industrial production,and makes the magnetic field manipulation of electrocatalysis become a challenging task.In this work,instead of the external magnetic field,a bias magnetic field is self-supplied by the remanence state of a ferromagnetic electrocatalyst of FePt.Owing to the assistance of this bias magnetic field,the FePt film in the remanence state shows the overpotential of 229 mV during hydrogen evolution reaction,which is much lower than that in its demagnetization state(283 mV).Our findings demonstrate that the remanence in ferromagnetic electrocatalysts can improve the catalytic performance,which is attributed to the decrease in domain walls.
基金Project supported by the National Key Research and Development Program of China(2022YFB3505201,2022YFB3505400)the National Natural Science Foundation of China(52261034)the Natural Science Foundation of Jiangxi Province(20224BAB204015)。
文摘It is still a challenge to simultaneously enhance coercivity(H_(cj))and remanence(J_(r))of hot-deformed Nd-Fe-B magnet due to the coercivity-remanence trade-off dilemma.Here,we achieved this balance between H_(cj)and Jr by flake Cu powder assisted DyF_(3)interflake addition.The Hcj increases from 1218 to 1496 kA/m and Jr increases from 1.32 to 1.34 T compared with the original magnet.Results show that the width of coarse grain layers reduces because of the introduction of flake Cu,which increases the contact areas of the adjacent grains at ribbon interfaces and suppresses the excessive growth of grains.The stronger degree of texture and higher density compared with the original magnet should take the responsibility for the increase of J_(r).Additionally,the aggregation regions of rare earth rich(RE-rich)phase reduce and the betterment of the microstructure is another reason for the enhancement of Jr in the flake Cu aided DyF_(3)hot-deformed magnet.This strategy of using flake powder additives provides a promising method for optimizing microstructure and enhancing magnetic properties of hot-deformed Nd-Fe-B magnets.
基金financially supported by the National Natural Science Foundation of China(Nos.51761145026 and 51471016)the Beijing Natural Science Foundation(No.2151002).
文摘Er-doped Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)magnets with a low remanence temperature coefficient were prepared by powder metallurgy method.The influence of Er content on the remanence and microstructure was investigated.X-ray diffractometer(XRD)analysis showed that the magnets with different Er contents consist of 2:17 R phase and 1:5 H phase.Scanning electron microscopy(SEM)analysis showed that the composition of the matrix is consistent with stoichiometric composition and no obvious precipitated phase appears.With the increase in doped Er amount,the temperature stability of Sm1-xErx(CobalFe0.15Cu0.08Zr0.03)7.8(x=0,0.1,0.2,0.3)is getting better.When x is up to 0.3,the magnets with a low remanence temperature coefficient are obtained and the remanence descends tardily from 0.86 to 0.80 T as the temperature rises from room temperature to 400℃.These results indicate that Er substitution for Sm in SmCobased permanent magnets together with optimal composition and proper heat treatment could achieve a desired magnetic performance combined with high thermal stability.
文摘The relation between microscopic properties (e.g., layer thickness, easy axis orientation) and the macroscopic magnetic properties such as remanent magnetization of the ferromagnetic multilayer system is investigated based on a simple micromagnet approach. We concentrate on a multilayer design with periodic boundary condition, where alternating soft/hard layers build a nanostructured multilayer. For any easy axis direction in the soft and hard layers a simple explicit expression of remanence of the system has been derived analytically. We find that the remanence clearly depends on the thickness of the soft magnetic layer and is nearly independent of the thickness of hard magnetic layer. On the other hand, the remanence increases upon reducing the angle enclosed by the saturation magnetization and the easy axis directions of soft magnetic layer. However, it is unsensitive to the easy axis direction of hard magnetic layer, but there exists a maximum remanence for a certain easy axis direction of hard magnetic layer.
文摘There are some abnormal phenomena in the test or operation of transformer, which are mainly caused by the residual magnetism in the core. Therefore, this paper briefly introduces the electromagnetic characteristics of ferromagnetic elements, and analyzes the mechanism of transformer remanence based on the electromagnetic characteristics. Finally, the influence of transformer remanence on transformer current, relay protection device, primary equipment and power quality is studied, and the corresponding preventive measures are put forward.
基金supported by the National Natural Science Foundation of China (41804067, 42174090, 42250101, and 42250103)the Science Research Project of the Hebei Education Department (BJK2024107)+3 种基金the Hebei Natural Science Foundation (D2022403044)the Opening Fund of the Key Laboratory of Geological Survey and Evaluation of the Ministry of Education (GLAB2023ZR02)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources (MSFGPMR2022-4)the Excellent Young Scientist Fund of Hebei GEO University (YQ202403)。
文摘The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic field polarity reversals,the oceanic lithosphere has significant remanent magnetization,which causes magnetic anomaly stripes parallel to the mid-ocean ridges.However,it is difficult to construct a high-resolution lithospheric magnetic field model in oceanic regions with relatively sparse data or no data.Using forward calculated lithospheric magnetic field data based on an oceanic remanent magnetization(ORM) model with physical and geological foundations as a supplement is a feasible approach.We first collect the latest available oceanic crust age grid,plate motion model,geomagnetic polarity timescale,and oceanic lithosphere thermal structure.Combining the assumptions that the paleo geomagnetic field is a geocentric axial dipole field and that the normal oceanic crust moves only in the horizontal direction,we construct a vertically integrated ORM model of the normal oceanic crust with a known age,including the intensity,inclination,and declination.Both the ORM model and the global induced magnetization(GIM) model are then scaled from two aspects between their forward calculated results and the lithospheric magnetic field model LCS-1.One aspect is the difference in their spherical harmonic power spectra,and the other is the misfit between the grid data over the oceans.We last compare the forward calculated lithospheric magnetic anomaly from the scaled ORM and GIM models with the Macao Science Satellite-1(MSS-1) observed data.The comparison results show that the magnetic anomalies over the normal oceanic crust regions at satellite altitude are mainly contributed by the high-intensity remanent magnetization corresponding to the Cretaceous magnetic quiet period.In these regions,the predicted and observed anomalies show good consistency in spatial distribution,whereas their amplitude differences vary across regions.This result suggests that regional ORM construction should be attempted in future work to address these amplitude discrepancies.
基金Project supported by the National Natural Science Foundation of China (No.60776027)
文摘This paper presents a security strategy for resisting a physical attack utilizing data remanence in powered- off static random access memory （SRAM）. Based on the mechanism of physical attack to data remanence, the strategy intends to erase data remanence in memory cells once the power supply is removed, which disturbs attackers trying to steal the right information. Novel on-chip secure circuits including secure power supply and erase transistor are integrated into conventional SRAM to realize erase operation. Implemented in 0.25μm Huahong-NEC CMOS technology, an SRAM exploiting the proposed security strategy shows the erase operation is accomplished within 0.2 μs and data remanence is successfully eliminated. Compared with conventional SRAM, the retentive time of data remanence is reduced by 82% while the operation power consumption only increases by 7%.
文摘Previous palaeomagnetic work shows that the mechanism of remanence acquisition on sediments is very complicated. Different magnetizing processes under different conditions may produce some anomalous magnetic signals which have nothing to do with the changes of the geomagnetic field and are difficult to explain.;The depositional remanent magnetization (DRM) may produce an inclination error and a bedding error, while postdepositional remanent magnetization (PDRM) may result in a time delay between the magnetic and sedimentary ages. When there are some different magnetic phases with different lock-in depths in the sediments, it is difficult to judge the depth of the reversal or excursion, or even the artificial magnetic signal may be produced. Even if there is only one magnetic phase in the sediment, the recorded magnetic signals may also be different if the lock-in depth is changed comparative to the lasting period of one reversal or excursion. Demagnetization may also change the primary magnetic records and the changes of water content may result in the displacement of magnetic boundary. The so-called "unstable core", representing subtle changes in mineralogy into and out of a self-reversal region or a viscous magnetization region, gives a complicated palaeomagnetic record with many apparent changes in the palaeomagnetic direction. Moreover, some physical disturbances, such as biodisturbance, deformation, drilling processes and drying effects, may result in the remanence alteration. Some palaeomagnetic investigations demonstrate that good magnetic signals are invariably achieved on homogenous mud or clay sediments, but the worse signals on inhomogeneous profiles, especially on sandy layers.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074220 and 11627805)the National Key Research and Development Program of China(Grant No.2023YFA1406604)。
文摘The melt-spun ribbons of nominal composition Pr_(9)Fe_(84.2-x)B_(6.2)P_(0.3)Zr_(0.3)Cu_(x)(x=0,0.5,1,2)were prepared at wheel speeds of 21 m·s^(-1),27 m·s^(-1),30 m·s^(-1),and 33 m·s^(-1).The XRD patterns show that as the wheel speed increases,the crystallinity of the 2:14:1 hard phase decreases,while that of theα-Fe soft phase increases.The(BH)_(max),remanence,and coercivity are improved from 63 kJ·m^(-3),0.85 T,and 515 kA·m^(-1)for the Cu-free ribbons to 171 kJ·m^(-3),1.08 T,and684 kA·m^(-1)with x=0.5.The high squareness ratio of J_(r)/J_(s)~0.82 at 0.5 at.%Cu(27 m·s^(-1))indicates strong exchange coupling due to small grain sizes of 15 nm and 30 nm for soft and hard magnetic phases,respectively.The SEM images revealed smooth morphology and uniform element distribution at 0.5 at.%Cu(27 m·s^(-1)),contributing to the high magnetic properties.The low recoil permeability(μrec)value of 5.466×10^(-4)T/kA·m^(-1)to 1.970×10^(-4)T/kA·m^(-1)confirms the strong exchange coupling with x=0.5(27m·s^(-1)).The initial magnetization curves show that the coercivity mechanism of the Cu-free alloy evolves from the nucleation of the reverse domain to the domain wall pinning as the wheel speed increases,resulting in a high coercivity value of 818 kA·m^(-1)(33 m·s^(-1)).Conversely,for the Cu-added alloy,the coercivity mechanism changes from pinning to the nucleation of the reverse domain from low to high wheel speed.
基金Project supported by the National Key Research and Development Program(2021YFB3502801,2021YFB3502803)the National Natural Science Foundation of China(52001067)。
文摘A novel Nd-Fe-B type permanent magnet with excellent thermal stability was designed by Co replacing Fe in the main phase and the grain boundary phase.The remanence and coercivity temperature coefficient reach 0.058%/℃and 0.465%/℃in the te mperature range from 25 to 100℃,which are much lower than those of commercial Nd-Fe-B magnet.An enhanced Curie temperature is obtained for the novel magnet due to the Co substitution,which significantly improves the operating temperature.The microstructure result reveals that an amorphous phase exists in the intergranular grains which is probably responsible for the deterioration of intrinsic coercivity.This work can provide a reference for the design and optimization of components of sintered Nd-Fe-B magnets with excellent thermal stability.
基金the Deanship of Scientific Research at King Khalid University for funding this work through the large group research project under grant number (RGP2/82/44)。
文摘Spinel ferrites exhibit exceptional magnetic properties,making them a distinctive class of magnetic materials.The sol-gel technique was utilized for the synthesis of spinel ferrites with the chemical formula Co_(0.6)Sr_(0.4)Ce_(x)Fe_(2-x)O_(4). Following that,a comprehensive X-ray diffraction analysis unveiled the crystalline cubic structure of the synthesized materials.Through the utilization of the M-H loop approach,the ferromagnetic attributes of ferrites were assessed,and the assimilation of rare earth elements led to substantial enhancements in saturation magnetization,remanence,and coercivity.Spinel ferrites with a high concentration of rare earth elements have improved direct current resistivity and activation energy.The logarithm of a material's resistance increased from 5.29 to 8.12 Ω·cm as cerium is added.With a change in the amount of cerium,the activation energy goes up from 0.19 to 0.29.By changing the frequency from 5.5 to 9.5 GHz,the dielectric characteristics were determined.As the frequency goes up,the dielectric constant goes down.Spinel ferrites that have been made better in every way can be used in high-frequency applications.
文摘The orientation of stable single domain (SSD) ferrimagnetic particles in an igneous rock sample was determined by a sensitive technique utilizing gyroremanent magnetization (GRM). Components of GRM were measured in the sample upon exposure to an alternating field (AF) at various orientations in 3 orthogonal planes. The major components of GRM exhibited a sin(2θ) dependence on AF orientation in the respective perpendicular planes. This was in accordance with theory [1] and contrary to some previously reported experimental results on magnetic recording tape, which produced a distorted sin(2θ) dependence of the GRM [1]. The explanation is likely due to the SSD ferrimagnetic particles in the rock sample being more dispersed (less interacting) compared to the highly interacting SSD particles in the magnetic tape sample of the previous study. The GRM results were consistent with another remanence anisotropy method, anisotropy of isothermal remanent magnetization (AIRM). This method again measures the anisotropy of the remanence carrying ferrimagnetic particles, but the IRM is also acquired by larger multidomain (MD) particles as well as by the SSD particles. The results were also consistent with the visible rock anisotropy (petrofabric), the anisotropy of magnetic susceptibility (AMS), and the shear wave velocity anisotropy. A comparison of all the methods demonstrated that the fine SSD particles, which make up only a small proportion of the rock, were aligned in quite a similar orientation to that of the main rock forming minerals that constituted the bulk of the sample.
基金the National HighTechnology Research and Development Program of China (No. 2007AA03Z438)the National Natural Science Foun-dation of China (No.50571028)the Beijing Municipal Science & Technology Commission, China (No. D0406002000091)
文摘The variations of intrinsic coercivity and remanence of sintered Nd-Fe-B magnets with ultra-high intrinsic coercivity were investigated. The results showed that the intrinsic coercivity and remanence declined simultaneously with increasing temperature, but the squareness of the magnets has hardly been changed. The temperature coefficients of remanence （α） and coercivity （β） for the magnets were calculated by two different methods, and the variations of the temperature coefficients and the microstructure of sintered Nd-Fe-B magnets were analyzed. The temperature coefficients of remanence （α） and coercivity （β） for the sintered magnets are very small, and the existence of fine microstructure is necessary to obtain sintered Nd-Fe-B magnets with ultra-high intrinsic coercivity.
基金Project supported by the National Natural Science Foundation of China (50261002 ,10574049)
文摘The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coereivity of the FePt based alloy as a function of the Nd content had maximum values, respectively.
基金financially supported by the National High-Tech R&D Program of China(No.2010AA03A401)the National Basic Research Program of China(No.2010CB934601)the National Nature Science Foundation of China(Nos.50931001and 51241009)
文摘Anisotropic CeCo4.325_xCuo.675Fex （x ： 0.475- 0.875） sintered magnets were prepared by traditional powder metallurgical method. Influence of ball-nfilling time and iron content on microstructure and magnetic properties of the CeCo4,325-xCuo.675Fex sintered magnets were investigated. It is shown that the properties of the magnet produced by mag- netic powders ball-milled for 40 min are better than that for 30 rain. With iron content increasing, remanence Br and maxi- mum energy product （BH）m increase first and then decrease. The optimal magnetic properties are obtained for the CeCo3.65Cuo.675Feo.675 sintered magnet： Br=0.685 T, the intrinsic coercivity Hci = 350 kA.m-1, and （BH）m ： 85.6 kJ.m-3. The increase of Br is mainly influenced by iron content of 1：5 matrix which can properly increase the saturation induction Bs; the rapid increase of the amount of Ce-rich phase and 5：19 phase gives rise to the deterioration of the magnets when x ≥ 0.775.
文摘Nanocrystalline Fe-based alloys offer a new opportunity for tailoring soft magnetic materials. Nanocrystalline alloy in the form of ribbon with the composition of Fe73.5Cu1Nb3Si13.5B9 was prepared by rapid quenching method for soft magnetic properties analysis. The rapidly quenched alloy has been annealed in a controlled way in the temperature range 490℃ to 680℃ and annealing time 1 min to 60 min. The study of the structural parameters has been investigated by means of XRD analysis. Magnetic properties were analyzed by measuring B-H loop and frequency dependence of initial permeability. Enhanced value of initial permeability by two orders of magnitude and very low value of relative loss factor of the order of 10–3 has been observed with the variation of annealing temperature and time. The initial permeability for the optimum annealed sample has been found 23,064 as compared with 360 for its amorphous counterpart. The initial permeability spectra show dispersion around 100 kHz. Magnetic hysteresis has been investigated by measuring B-H loops at various magnetic fields for different annealing temperature and time. The coercivity and remanence has been found to decrease significantly for optimized annealed condition compared to as-cast state. The core loss of the samples decreases with the annealing time which indicates the good magnetic property of soft magnetic materials.
文摘In order to improve and stabilize the magnetic properties of nanocomposite Nd2Fe14B/α-Fe magnetic alloys by a compositional adjustment, small amount of Dy and/or Co was added to Nd9Fe84B7 alloys. DTA analysis on the amorphous of the alloys took place as the soft magnetic phases were crystallized, and then the hard magnetic Nd2Fe14B was precipitated from them. While α-Fe and a metastable 1:7 (TbCu7-type) phase were formed simultaneously in Dy and Co-free alloys, they were crystallized separately at different temperatures after Dy or Co was added. This phase separation occurred more clearly in the Dy-treated alloys and the other soft magnetic phase Fe3B was also stabilized by Dy and/or Co. The 1: 7 phase that was stabilized by Dy and/or Co was not eliminated at 700 ℃, decreasing magnetic properties of the alloys. It was eventually disappeared above 725 ℃, but Fe3B was not eliminated even at 750 ℃ when Dy was added more than 0.5 at% or Co was added more than 2.0 at%. Amount of Nd2Fe14B in the alloys tended to increase as Dy addition increased,whereas Co addition did not lead to any appreciable change in the ratio of α-Fe and Nd2Fe14B. Moreover, Dy addition apparently increased coercivity of an alloy while Co addition had a beneficial effect on remanence. The grains in the Dytreated alloys were usually finer than those in the Co-treated alloys. The grain size of both α-Fe and Nd2Fe14B in the alloys exhibiting mr ≥ 0.72 was in the range of 20 ～ 40 nm or even larger 50 nm, which is larger than the theoretical optimum size ( ～ 10 nm). Typical magnetic properties obtained from a Nd7.5Dy1.5Fe82.5Co1.5B7 alloy annealed for 12 min at 725 ℃were iHc=4.85 kOe, Br= 11.32 kG, (BH)max = 15.73 MGOe, and mr=0.73.
