Influence of Cu substitution for Mn on the structure, magnetic, magnetocaloric and magnetoresistance properties of La0.7Sr0.3NnO3 perovskites

Structural, magnetic, magnetocaloric and magneto resistance (MR) studies on La0.7Sr0.3Mn0.95Cu0.05O3 (No. 1) and La0.7Sr0.3Mn0.9Cu0.1O3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermornagnetic measurements for both compositions at low field indicate that a spin-glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, T-C, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, DeltaS(max) of 1.96 and 2.07 J/kg K at 13.5 kOe and 350 K is observed for sample No. I and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for T < T-C and semiconductor for T > T-C; moreover, the MR is maximal around Tc. (C) 2002 Elsevier Science B.V. All rights reserved.