Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge orderi...Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge ordering phase of La0.4Ca0.6MnO3 was studied through the measurements of X-ray diffraction （XRD）, magnetization-temperature （M-T） curves and electron spin resonance （ESR） spectra. The experimental results indicate that the mother＇s body of La0.4Ca0.6MnO3 has very complicated magnetic structure, exhibits charge ordering phase at 258 K, and shows long-range strongly correlated charge ordering-antiferromagnetism （CO-AFM） phase from 175 to 50 K. Spin glass state appears when the temperature decreases to about 41 K. When the Cr substitution amount is x = 0.06, the charge ordering phase of the mother＇s body is de-stroyed, because the Cr3＋ substitution for Mn3＋ destroys the spin order of CE-type antiferromagnetism, and thus leads to the melting of charge ordering. It is verified experimentally that the strong coupling between charge order and spin order exists in the charge order system of CE-type antiferromagnetism.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
Single phase polycrystalline samples Na0.7Co1-xAlxO2 （x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 030） were prepared by solid state reaction. The magnetic properties from 5 K to 300 K have been studied by dc and ac magneti...Single phase polycrystalline samples Na0.7Co1-xAlxO2 （x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 030） were prepared by solid state reaction. The magnetic properties from 5 K to 300 K have been studied by dc and ac magnetic susceptibility measurements. Samples with lower doping quantity （x = 0, 0.05, 0.10） showed paramagnetic behaviors, but those with higher doping quantity （x=0.20, 0.25, 0.30）showed spin-glass behaviors with a freezing temperature （Tf） of about 13 K.展开更多
At low temperatures the configurational phase space of a macroscopic complex system （e.g., a spin-glass） of N - 10^23 interacting particles may split into an exponential number Ωs - exp（const × N） of ergodic...At low temperatures the configurational phase space of a macroscopic complex system （e.g., a spin-glass） of N - 10^23 interacting particles may split into an exponential number Ωs - exp（const × N） of ergodic sub-spaces （thermodynamic states）. It is usually assumed that the equilibrium collective behavior of such a system is determined by its ground thermodynamic states of the minimal free-energy density, and that the equilibrium free energies follow the distribution of exponentied decay. But actually for some complex systems, the equilibrium free-energy values may follow a Gaussian distribution within an intermediate temperature range, and consequently their equilibrium properties are contributed by excited thermodynamic states. Based on this analysis, the re-weighting parameter y in the cavity approach of spin-glasses is easily understood. Depending on the free-energy distribution, the optimal y can either be equal to or be strictly less than the inverse temperature β.展开更多
基金supported by the Key Program of the National Natural Science Foundation of China (No.19934003)the Key Program of Natural Science Research of Anhui Education Department (No.KJ2011A259+3 种基金 KJ2008A34ZC)the Natural Science Research Programs of Anhui Education Department, China (No.KJ2010B229No.KJ2010B228No.KJ2009B281Z)
文摘Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge ordering phase of La0.4Ca0.6MnO3 was studied through the measurements of X-ray diffraction （XRD）, magnetization-temperature （M-T） curves and electron spin resonance （ESR） spectra. The experimental results indicate that the mother＇s body of La0.4Ca0.6MnO3 has very complicated magnetic structure, exhibits charge ordering phase at 258 K, and shows long-range strongly correlated charge ordering-antiferromagnetism （CO-AFM） phase from 175 to 50 K. Spin glass state appears when the temperature decreases to about 41 K. When the Cr substitution amount is x = 0.06, the charge ordering phase of the mother＇s body is de-stroyed, because the Cr3＋ substitution for Mn3＋ destroys the spin order of CE-type antiferromagnetism, and thus leads to the melting of charge ordering. It is verified experimentally that the strong coupling between charge order and spin order exists in the charge order system of CE-type antiferromagnetism.
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.
基金This work was supported by the National Science Foundation of China under Grant No. 50372052, 50430137, 50588201 the National Basic Research Program of China (973 program), under Grant No. 2007CB616906)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in UniversityAustralian Research Council under Grant No. DP0559872, DP0881739.
文摘Single phase polycrystalline samples Na0.7Co1-xAlxO2 （x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 030） were prepared by solid state reaction. The magnetic properties from 5 K to 300 K have been studied by dc and ac magnetic susceptibility measurements. Samples with lower doping quantity （x = 0, 0.05, 0.10） showed paramagnetic behaviors, but those with higher doping quantity （x=0.20, 0.25, 0.30）showed spin-glass behaviors with a freezing temperature （Tf） of about 13 K.
基金supported by National Natural Science Foundation of China under Grant No.10774150
文摘At low temperatures the configurational phase space of a macroscopic complex system （e.g., a spin-glass） of N - 10^23 interacting particles may split into an exponential number Ωs - exp（const × N） of ergodic sub-spaces （thermodynamic states）. It is usually assumed that the equilibrium collective behavior of such a system is determined by its ground thermodynamic states of the minimal free-energy density, and that the equilibrium free energies follow the distribution of exponentied decay. But actually for some complex systems, the equilibrium free-energy values may follow a Gaussian distribution within an intermediate temperature range, and consequently their equilibrium properties are contributed by excited thermodynamic states. Based on this analysis, the re-weighting parameter y in the cavity approach of spin-glasses is easily understood. Depending on the free-energy distribution, the optimal y can either be equal to or be strictly less than the inverse temperature β.
