Cr 替代 Mn 对 La0.4Ca0.6MnO3 磁性质的影响

无机材料学报, 2011, 26(4): 411-416. doi: 10.3724/SP.J.1077.2011.00411

Cr 替代 Mn 对 La_0.4Ca_0.6MnO₃ 磁性质的影响

1.1. 自旋电子与纳米材料安徽省重点实验室培育基地 , 宿州 234000

3. 3. 中国科学技术大学合肥微尺度物质科学国家实验室 , 合肥 230026

1.1. Cultivating Base of Anhui Key Laboratory of Spintronic and Nanometric Materials, Suzhou 234000, China

2. 2. Department of Electronics and Electric Engineering, Suzhou College, Suzhou 234000, China

3. 3. Hefei National Laboratory of Micro-scale Matter Science, University of Science and Technology of China, Hefei 230026, China

基金项目: 国家自然科学基金重点项目 (19934003) 安徽省教育厅自然科学研究项目 (KJ2008A19ZC, KJ2008A34ZC, KJ2009B281Z, KJ2010B228, KJ2010B229)

关键词： La_0.4La_0.6MnO₃ , Cr-doping , charge ordering , spin-glass state

Influence of the Substitution of Cr for Mn on Magnetic Properties of La_0.4Ca_0.6MnO₃

WANG Gui-Ying , YANG Gang , GUO Huan-Yin ,

Keywords： La_0.4Ca_o.6MnO₃ , Cr掺杂 , 电荷有序 , 自旋玻璃

用固相反应法制备了La_0.4Ca_0.6Mn_1-xCr_xO₃(x=0.00,0.02,0.04,0.06,0.08,0.10,0.15)多晶样品, 通过X射线衍射(XRD)图谱、磁化强度-温度(M-T)曲线、电子自旋共振(ESR)谱线, 研究了Cr替代Mn对La_0.4Ca_0.6MnO₃磁性质的影响. 实验结果表明:La_0.4Ca_0.6MnO₃存在复杂的磁结构, 在258K出现电荷有序相, 从175K到50K, 产生强关联CO-AFM(电荷有序-反铁磁)相, 温度降到41K左右出现自旋玻璃态; 当替代量x≥0.06 时, 电荷有序相被融化; 当x≥0.10时, 自旋玻璃态被融化. 对实验结果进行了初步解释: 电荷有序相被融化主要原因是Cr³⁺与Mn⁴⁺具有相同的电子结构, Cr³⁺替代Mn³⁺破坏了CE型反铁磁的自旋序, 从而引起电荷序的坍塌, 实验证明了电荷序CE型反铁磁体系中, 电荷序和自旋序之间存在强耦合相互作用; 自旋玻璃态的融化, 是由于Cr替代Mn破坏了自旋玻璃态的生成条件, 即反铁磁背景下有少量铁磁成分 .

Polycrystalline samples of La_0.4Ca_o.6Mn₁ _-_xCr _xO₃ ( x =0.00,0.02,0.04,0.06,0.08,0.10,0.15 ) were prepared by t he solid state reaction method. The influence of Cr³⁺ substitution for Mn³⁺ on the magnetic property and charge ordering phase of La_0.4Ca_0.6MnO₃was 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 sample of La_0.4Ca_0.6MnO₃ has very complicated magnetic structure. The charge ordering phase of the sample exhibits at 258K, and strong correlated CO-AFM phase shows from 175K to 50K. The spin glass state of the sample appears when the temperature decreases to about 41K. When the Cr substitution amount x is more than 0.06, the charge ordering phase of the sample is destroyed. When x is larger than 0.10, spin-glass state is melt. In addition, experimental resu lts are explained preliminarily as follows: because Cr³⁺ and Mn⁴⁺ have the same electronic structure, Cr³⁺ substitution for Mn³⁺ destroys the spin order of CE-type antiferromagnetism, and thus leads to the destruction of charge ordering. It is verified experimentally that the strong coupling between charge ordering and spin ordering exists in the charge order system of CE-type anti-ferromagnetism, and Cr³⁺ substitution for Mn³⁺ destroys formation conditions of spin-glass state that small ferromagnetic component exists at the background of antiferromagnetism.

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