Enhancement of magnetoresistance in La2/3Ca1/3MnO3/xCuMn2O4 nanocomposites
Enhancement of magnetoresistance in La2/3Ca1/3MnO3/xCuMn2O4 nanocomposites
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DOI：
10.1088/0022-3727/40/3/002
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发表时间：
2007-02
期刊：
影响因子：
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通讯作者：
J. Miao;S. Yuan;G. Ren;X. Xiao;Gongqi Yu;Yongqiang Wang;S. Yin
中科院分区：
文献类型：
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作者：
J. Miao;S. Yuan;G. Ren;X. Xiao;Gongqi Yu;Yongqiang Wang;S. Yin
采用柠檬酸盐凝胶法制备了La 2/3Ca 1/3 MnO 3（LCMO）/xCuMn 2 O 4（0 × 40%）纳米复合材料，并对其微观结构和磁输运性能进行了表征。结果表明，与CuMn 2 O 4的制备具有重要的影响的电输运行为的复合材料。随着CuMn_2 O_4含量x的增加，复合材料的金属-绝缘体转变温度TMI下移，电阻率增大。磁化率分析表明，x = 4，20，30和40%的复合材料具有相近的顺磁-铁磁转变温度TC <240 K，低于纯LCMO的TC（<262 K）。电阻率（ρ）数据的高温（T > TMI）半导电部分遵循小极化子跳跃导电机制，并且样品的金属行为（T < TMI）符合载流子的电子-磁振子散射模型。此外，在低场磁电阻（LFMR）和高场磁电阻（MR）的显着增强观察到的复合材料在一个较宽的温度范围内低于TMI。x = 40%的样品在0.3T下测得的LFMR在T = 10 K时达到最大值，为1.23%，远大于纯LCMO的LFMR（1.69%）。我们认为，这样的增强MR是由于增强的自旋极化隧穿，这是操纵的自旋无序在LCMO表面所造成的CuMn 2 O 4此外。
Nanocomposites of La2/3Ca1/3MnO3(LCMO)/xCuMn2O4 (0 ⩽ x ⩽ 40%) have been prepared by a citrate gel route and characterized for microstructural and magnetotransport properties. Results show that fabrication with CuMn2O4 has an important effect on the electrical transport behaviour of the composites. With the increment of CuMn2O4 content x, the metal–insulator transition temperature TMI for the composites shifts downwards and the resistivity increases. The susceptibility analysis indicates that the composites with x = 4, 20, 30 and 40% have a similar paramagnetic–ferromagnetic transition temperature TC ∼ 240 K, which is lower than TC of pure LCMO (∼262 K). The high temperature (T > TMI) semi-conducting part of the resistivity (ρ) data follows a small polaron hopping conduction mechanism, and the metallic behaviour of the samples (T < TMI) fits the model in terms of electron–magnon scattering of the carriers. Furthermore, a significant enhancement both in low-field magnetoresistance (LFMR) and in high-field magnetoresistance (MR) is observed for the composites at a wide temperature range below TMI. The LFMR measured at 0.3 T reaches the maximum for the x = 40% sample when T = 10 K with the value of ∼23%, which is much larger than that of the pure LCMO (∼6.9%). We argue that such an enhancement in MR is attributed to the enhanced spin-polarized tunnelling, which is manipulated by the spin disorder at the LCMO surfaces caused by CuMn2O4 addition.