The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal field is studied within themean-field theory.The phase diagrams and magnetization curves are obtained by diagonalizing the Hamiltonian H_i of...The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal field is studied within themean-field theory.The phase diagrams and magnetization curves are obtained by diagonalizing the Hamiltonian H_i ofthe Ising system numerically,and the first order-order phase transitions,the first order-disorder phase transitions,andthe second-order phase transitions are discussed in details.Reentrant phenomena occur when the value of the transversefield is not zero and the reentrant diagram is given.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
The polycrystalline samples of Pro.45（Ca1-xSrx）0.55MnO3 （x = 0.0, 0.2, 0.4, 0.6） were prepared by solid-state reaction. Influence of Sr2＋ substitution for Ca2＋ at A site on magnetism was studied through the meas...The polycrystalline samples of Pro.45（Ca1-xSrx）0.55MnO3 （x = 0.0, 0.2, 0.4, 0.6） were prepared by solid-state reaction. Influence of Sr2＋ substitution for Ca2＋ at A site on magnetism was studied through the measurements of X-ray diffraction （XRD） spectrum, the magnetization-temperature （M-T） curves and electron spin resonance （ESR） curves. The results show that the magnetism strengthens and charge ordering weakens gradually with the increase of Sr2＋ substitution amount, respectively. The transition of paramagnetism（PM）-antiferromagnetism（AFM） occurs below the transition temperature of charge ordering （Tco）, and there is tittle ferromagnetic phase in the antiferromagnetic background at the lower temperature, which results in complex magnetic phases of the samples. Ferromagnetic clusters appear and grow larger with the increase of substitution amount./n addition, the reentrant spin-glass behavior appears at about 41 K. The magnetism phenomenon of the samples is mainly due to the competition between double exchange and Jahn-Teller coupling. The Jahn-Teller coupling becomes weak, and the double exchange wins the advantage in the competition with the increase of substitution amount, which leads to the magnetism variation of the system.展开更多
基金Ph.D.Programs Foundation of Ministry of Education of China under Grant No.20040145019
文摘The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal field is studied within themean-field theory.The phase diagrams and magnetization curves are obtained by diagonalizing the Hamiltonian H_i ofthe Ising system numerically,and the first order-order phase transitions,the first order-disorder phase transitions,andthe second-order phase transitions are discussed in details.Reentrant phenomena occur when the value of the transversefield is not zero and the reentrant diagram is given.
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。
基金financially supported by the National Natural Foundation of China (Grant No.19934003)the Natural Science Research Key Program of Anhui Educational Committee (KJ2011A259)the Cultivating Base of Anhui Key Laboratory of Spintronics and Nano-materials Research Program(No.2010YKF04)
文摘The polycrystalline samples of Pro.45（Ca1-xSrx）0.55MnO3 （x = 0.0, 0.2, 0.4, 0.6） were prepared by solid-state reaction. Influence of Sr2＋ substitution for Ca2＋ at A site on magnetism was studied through the measurements of X-ray diffraction （XRD） spectrum, the magnetization-temperature （M-T） curves and electron spin resonance （ESR） curves. The results show that the magnetism strengthens and charge ordering weakens gradually with the increase of Sr2＋ substitution amount, respectively. The transition of paramagnetism（PM）-antiferromagnetism（AFM） occurs below the transition temperature of charge ordering （Tco）, and there is tittle ferromagnetic phase in the antiferromagnetic background at the lower temperature, which results in complex magnetic phases of the samples. Ferromagnetic clusters appear and grow larger with the increase of substitution amount./n addition, the reentrant spin-glass behavior appears at about 41 K. The magnetism phenomenon of the samples is mainly due to the competition between double exchange and Jahn-Teller coupling. The Jahn-Teller coupling becomes weak, and the double exchange wins the advantage in the competition with the increase of substitution amount, which leads to the magnetism variation of the system.
