Enhancement of magnetoresistance in La2/3Ca1/3MnO3/xCuMn2O4 nanocomposites

Abstract

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.