In this work,the computational complexity of a spin-glass three-dimensional(3D)Ising model(for the lattice sizeN=lmn,wherel,m,n are thenumbersof lattice points along three crystallographic directions)is studied.We pro...In this work,the computational complexity of a spin-glass three-dimensional(3D)Ising model(for the lattice sizeN=lmn,wherel,m,n are thenumbersof lattice points along three crystallographic directions)is studied.We prove that an absolute minimum core(AMC)model consisting of a spin-glass 2D Ising model interacting with its nearest neighboring plane,has its computational complexity O(2mn).Any algorithms to make the model smaller(or simpler)than the AMC model will cut the basic element of the spin-glass 3D Ising model and lost many important information of the original model.Therefore,the computational complexity of the spin-glass 3D Ising model cannot be reduced to be less than O(2mn)by any algorithms,which is in subexponential time,superpolynomial.展开更多
We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current（AC） susceptibility,AC heat capacity and electrical resistivity measurements under pressu...We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current（AC） susceptibility,AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa.A detailed magnetic phase diagram under pressure is determined.GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions,respectively,at temperatures TC= 20.5 K,T1= 18.0 K and TN= 11.5 K under ambient pressure.Under pressures up to 2.2 GPa,these anomalies are observed to slightly increase at TCand T1,and they coincide with each other above 1.6 GPa.Conversely,they decrease at TN and disappear under pressures higher than 1.4 GPa.The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure.Moreover,the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization,aging effect and frequency dependence of AC susceptibility.A separation between the zero-field-cooled（ZFC） and field-cooled（FC） magnetization curves becomes evident at a low magnetic field of 0.001 T.A long-time relaxation behavior is observed at 4 K.The freezing temperature Tfincreases with frequency increasing.展开更多
Ergodicity of a spin-glass is broken at low temperatures;the system is trapped in one of many ergodicconfigurational domains.Transitions between different ergodic domains are achievable through a heating-annealingproc...Ergodicity of a spin-glass is broken at low temperatures;the system is trapped in one of many ergodicconfigurational domains.Transitions between different ergodic domains are achievable through a heating-annealingprocedure.If this experiment is repeated infinite times,all ergodic configurational domains will be visited with frequencesthat decreasing exponentially with their free energies.The mean free energy density of a spin-glass system on a randomgraph is calculated based on this free energy Boltzmann distribution in the present work,by means of the cavity approach.展开更多
We report the successful fabrication of a new 1111-type bulk magnetic semiconductor(La,Ba)(Zn,Mn)SbO through the solid solution of(La,Ba)and(Zn,Mn)in the parent compound LaZnSbO.The polycrystalline samples(La,Ba)(Zn,M...We report the successful fabrication of a new 1111-type bulk magnetic semiconductor(La,Ba)(Zn,Mn)SbO through the solid solution of(La,Ba)and(Zn,Mn)in the parent compound LaZnSbO.The polycrystalline samples(La,Ba)(Zn,Mn)SbO crystallize into ZrCuSiAs-type tetragonal structure,which has the same structure as iron-based superconductor LaFeAsO_(1-δ).The DC magnetization measurements indicate the existence of spin-glass ordering,and the coercive field is up to~11500 Oe(1 Oe=79.5775 A·m^(-1)).The AC magnetic susceptibility further determines that the samples evolve into a conventional spin-glass ordering state below the spin freezing temperature T_(f).In addition,the negative magnetoresistance(MR≡[ρ(H)-ρ(0)]/ρ(0))reaches-88%under 9 T.展开更多
We study the statistical properties of an ensemble of disordered 1D spatial spin-chains (SSCs) of certain length in the external field. On nodes of spin-chain lattice the recurrent equations and corresponding inequal-...We study the statistical properties of an ensemble of disordered 1D spatial spin-chains (SSCs) of certain length in the external field. On nodes of spin-chain lattice the recurrent equations and corresponding inequal-ity conditions are obtained for calculation of local minimum of a classical Hamiltonian. Using these equa-tions for simulation of a model of 1D spin-glass an original high-performance parallel algorithm is developed. Distributions of different parameters of unperturbed spin-glass are calculated. It is analytically proved and shown by numerical calculations that the distribution of the spin-spin interaction constant in the Heisenberg nearest-neighboring Hamiltonian model as opposed to the widely used Gauss-Edwards-Anderson distribu-tion satisfies the Lévy alpha-stable distribution law which does not have variance. We have studied critical properties of spin-glass depending on the external field amplitude and have shown that even at weak external fields in the system strong frustrations arise. It is shown that frustrations have a fractal character, they are self-similar and do not disappear at decreasing of calculations area scale. After averaging over the fractal structures the mean values of polarizations of the spin-glass on the scales of external field's space-time peri-ods are obtained. Similarly, Edwards-Anderson’s ordering parameter depending on the external field ampli-tude is calculated. It is shown that the mean values of polarizations and the ordering parameter depending on the external field demonstrate phase transitions of first-order.展开更多
Single phase of Fe^3＋-doped α-Ga2-xFexO3（α-GF x O, x = 0.1, 0.2, 0.3, 0.4） is synthesized by treating the β-Ga2-x Fe x O3（β-GF x O） precursors at high temperatures and high pressures. Rietveld refinements of ...Single phase of Fe^3＋-doped α-Ga2-xFexO3（α-GF x O, x = 0.1, 0.2, 0.3, 0.4） is synthesized by treating the β-Ga2-x Fe x O3（β-GF x O） precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe^3＋content. Calorimetric measurements show that the temperature of the phase transition from α-GF x O to β-GF x O increases, while the associated enthalpy change decreases upon increasing Fe^3＋content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3＋content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe^3＋ions is antiferromagnetic. Remnant magnetization is observed in the Fe^3＋-doped α-GF x O and is attributed to the spin glass in the magnetic sublattice. At high Fe^3＋doping level（x = 0.4）, two evident peaks are observed in the image part of the AC susceptibility χ ac. The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α-GF0.4O is suggested to be the behavior of two spin glasses.展开更多
For the first time, a novel material of La1-x- TexMnO3 (x = 0.04, 0.1), in which the La ions are replaced by the nonmetal element Te in the Chalcogen, has been synthesized. The material has a rhombohedral lattice with...For the first time, a novel material of La1-x- TexMnO3 (x = 0.04, 0.1), in which the La ions are replaced by the nonmetal element Te in the Chalcogen, has been synthesized. The material has a rhombohedral lattice with the space group of R3c, and Te ions have a tetravalence state. The curves of the resistivity vs. temperature indicate that this material has the property of a metal-semiconductor transition and the colossal magnetoresistance (CMR) effect. The maximum magnetoreistance ratio MR=[(0)()]/(0)H? is about 51% at 4 T for x = 0.1. Besides, a spin-glass behavior at low magnetic fields is observed in this compound.展开更多
We report the manipulation of ferromagnetism in magnetic semiconductor Ba(Zn,Mn,Cu)_(2)As_(2)through chemical pressure.The substitutions of Sr for Ba and Sb for As introduce positive and negative chemical pressures,re...We report the manipulation of ferromagnetism in magnetic semiconductor Ba(Zn,Mn,Cu)_(2)As_(2)through chemical pressure.The substitutions of Sr for Ba and Sb for As introduce positive and negative chemical pressures,respectively;neither Sr doping nor Sb doping change the tetragonal crystal structure.Based on Ba(Zn_(0.75)Mn_(0.125)Cu_(0.125))_(2)As_(2)with T_(C)~34 K,10%Sr/Ba substitutions significantly improve T_(C)by~15%to 39 K,whereas 10%Sb/As substitutions substantially reduce TCby~47%to 18 K.The AC magnetic susceptibility measurements indicate that Sr-doped and Sb-doped samples evolve into a spin glass state below the spin freezing temperature Tf.Electrical transport measurements demonstrate that Sr-doped specimens retain semiconducting behavior;additionally,they display a significant negative magnetoresistance effect under applied magnetic fields and the magnetoresistance reaches~-19%at 8 T.展开更多
通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝...通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。展开更多
基金This work has been supported by the National Natural Science Foundation of China under grant numbers 51590883 and 51331006by the State Key Project of Research and Development of China(No.2017YFA0206302).
文摘In this work,the computational complexity of a spin-glass three-dimensional(3D)Ising model(for the lattice sizeN=lmn,wherel,m,n are thenumbersof lattice points along three crystallographic directions)is studied.We prove that an absolute minimum core(AMC)model consisting of a spin-glass 2D Ising model interacting with its nearest neighboring plane,has its computational complexity O(2mn).Any algorithms to make the model smaller(or simpler)than the AMC model will cut the basic element of the spin-glass 3D Ising model and lost many important information of the original model.Therefore,the computational complexity of the spin-glass 3D Ising model cannot be reduced to be less than O(2mn)by any algorithms,which is in subexponential time,superpolynomial.
基金Project supported by JSPS KAKENHI(Grant No.24540366,Grant-in-Aid for Scientific Research(C))
文摘We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current（AC） susceptibility,AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa.A detailed magnetic phase diagram under pressure is determined.GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions,respectively,at temperatures TC= 20.5 K,T1= 18.0 K and TN= 11.5 K under ambient pressure.Under pressures up to 2.2 GPa,these anomalies are observed to slightly increase at TCand T1,and they coincide with each other above 1.6 GPa.Conversely,they decrease at TN and disappear under pressures higher than 1.4 GPa.The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure.Moreover,the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization,aging effect and frequency dependence of AC susceptibility.A separation between the zero-field-cooled（ZFC） and field-cooled（FC） magnetization curves becomes evident at a low magnetic field of 0.001 T.A long-time relaxation behavior is observed at 4 K.The freezing temperature Tfincreases with frequency increasing.
文摘Ergodicity of a spin-glass is broken at low temperatures;the system is trapped in one of many ergodicconfigurational domains.Transitions between different ergodic domains are achievable through a heating-annealingprocedure.If this experiment is repeated infinite times,all ergodic configurational domains will be visited with frequencesthat decreasing exponentially with their free energies.The mean free energy density of a spin-glass system on a randomgraph is calculated based on this free energy Boltzmann distribution in the present work,by means of the cavity approach.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2022YFA1402701 and 2022YFA1403202)the National Natural Science Foundation of China (Grant No.12074333)the Key Research and Development Program of Zhejiang Province,China (Grant No.2021C01002)。
文摘We report the successful fabrication of a new 1111-type bulk magnetic semiconductor(La,Ba)(Zn,Mn)SbO through the solid solution of(La,Ba)and(Zn,Mn)in the parent compound LaZnSbO.The polycrystalline samples(La,Ba)(Zn,Mn)SbO crystallize into ZrCuSiAs-type tetragonal structure,which has the same structure as iron-based superconductor LaFeAsO_(1-δ).The DC magnetization measurements indicate the existence of spin-glass ordering,and the coercive field is up to~11500 Oe(1 Oe=79.5775 A·m^(-1)).The AC magnetic susceptibility further determines that the samples evolve into a conventional spin-glass ordering state below the spin freezing temperature T_(f).In addition,the negative magnetoresistance(MR≡[ρ(H)-ρ(0)]/ρ(0))reaches-88%under 9 T.
文摘We study the statistical properties of an ensemble of disordered 1D spatial spin-chains (SSCs) of certain length in the external field. On nodes of spin-chain lattice the recurrent equations and corresponding inequal-ity conditions are obtained for calculation of local minimum of a classical Hamiltonian. Using these equa-tions for simulation of a model of 1D spin-glass an original high-performance parallel algorithm is developed. Distributions of different parameters of unperturbed spin-glass are calculated. It is analytically proved and shown by numerical calculations that the distribution of the spin-spin interaction constant in the Heisenberg nearest-neighboring Hamiltonian model as opposed to the widely used Gauss-Edwards-Anderson distribu-tion satisfies the Lévy alpha-stable distribution law which does not have variance. We have studied critical properties of spin-glass depending on the external field amplitude and have shown that even at weak external fields in the system strong frustrations arise. It is shown that frustrations have a fractal character, they are self-similar and do not disappear at decreasing of calculations area scale. After averaging over the fractal structures the mean values of polarizations of the spin-glass on the scales of external field's space-time peri-ods are obtained. Similarly, Edwards-Anderson’s ordering parameter depending on the external field ampli-tude is calculated. It is shown that the mean values of polarizations and the ordering parameter depending on the external field demonstrate phase transitions of first-order.
基金supported by the National Basic Research Program of China(Grant No.2010CB731605)the National Science Fund for Distinguished Young Scholars of China(Grant No.51025103)+3 种基金the National Natural Science Foundation of China(Grant Nos.51172198 and 51102206)the Natural Science Foundation of Hebei Province,China(Grant No.E2014203144)the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province,China(Grant No.YQ2014009)the Research Program of the College Science&Technology of Hebei Province,China(Grant No.QN2014047)
文摘Single phase of Fe^3＋-doped α-Ga2-xFexO3（α-GF x O, x = 0.1, 0.2, 0.3, 0.4） is synthesized by treating the β-Ga2-x Fe x O3（β-GF x O） precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe^3＋content. Calorimetric measurements show that the temperature of the phase transition from α-GF x O to β-GF x O increases, while the associated enthalpy change decreases upon increasing Fe^3＋content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3＋content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe^3＋ions is antiferromagnetic. Remnant magnetization is observed in the Fe^3＋-doped α-GF x O and is attributed to the spin glass in the magnetic sublattice. At high Fe^3＋doping level（x = 0.4）, two evident peaks are observed in the image part of the AC susceptibility χ ac. The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α-GF0.4O is suggested to be the behavior of two spin glasses.
基金supported by the State Key Program of China(Grant No.G1998061412).
文摘For the first time, a novel material of La1-x- TexMnO3 (x = 0.04, 0.1), in which the La ions are replaced by the nonmetal element Te in the Chalcogen, has been synthesized. The material has a rhombohedral lattice with the space group of R3c, and Te ions have a tetravalence state. The curves of the resistivity vs. temperature indicate that this material has the property of a metal-semiconductor transition and the colossal magnetoresistance (CMR) effect. The maximum magnetoreistance ratio MR=[(0)()]/(0)H? is about 51% at 4 T for x = 0.1. Besides, a spin-glass behavior at low magnetic fields is observed in this compound.
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1402701 and 2022YFA1403202)the National Natural Science Foundation of China(Grant No.12074333)the Key Research and Development Program of Zhejiang Province,China(Grant No.2021C01002)。
文摘We report the manipulation of ferromagnetism in magnetic semiconductor Ba(Zn,Mn,Cu)_(2)As_(2)through chemical pressure.The substitutions of Sr for Ba and Sb for As introduce positive and negative chemical pressures,respectively;neither Sr doping nor Sb doping change the tetragonal crystal structure.Based on Ba(Zn_(0.75)Mn_(0.125)Cu_(0.125))_(2)As_(2)with T_(C)~34 K,10%Sr/Ba substitutions significantly improve T_(C)by~15%to 39 K,whereas 10%Sb/As substitutions substantially reduce TCby~47%to 18 K.The AC magnetic susceptibility measurements indicate that Sr-doped and Sb-doped samples evolve into a spin glass state below the spin freezing temperature Tf.Electrical transport measurements demonstrate that Sr-doped specimens retain semiconducting behavior;additionally,they display a significant negative magnetoresistance effect under applied magnetic fields and the magnetoresistance reaches~-19%at 8 T.
文摘通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。
