Large magnetocaloric effect and critical behavior in Cu-doped nanocrystalline La0.7Te0.3Mn1-yCuyO3 (0.1 ≤ y ≤ 0.5)

Abstract

The impact of copper doping on the magnetic properties and critical behavior of the nanocrystalline La0.7Te0.3Mn1-yCuyO3 (0.1 ≤ y ≤ 0.5) system has been explored. The powder X-ray diffraction (XRD) patterns affirmed the single crystal phase for all samples without any detectable secondary phase. We have observed rhombohedral (R3‾c space group) crystal symmetry for y ≤ 0.3. With the increase in copper doping composition (y = 0.4 and 0.5) structure changes to orthorhombic (Pbnm space group). The temperature-dependent magnetization data suggests a paramagnetic (PM) to ferromagnetic (FM) phase transition upon cooling for all compositions. The Curie temperature TC is almost constant (about 226 K) for the compositions y ≤ 0.3 and after that TC decreases from 154 K (y = 0.4) to 91 K (y = 0.5). The maximal values of magnetic entropy change |ΔSMmax| were obtained from a series of magnetic isotherms and were observed to be 4.59 J/(kg-K), 4.84 J/(kg-K), 3.92 J/(kg-K), 2.49 J/(kg-K) and 1.56 J/(kg-K) for y = 0.1, 0.2, 0.3, 0.4 and 0.5 respectively up to a field change of 5 T. The critical behavior at PM-FM transition for all the samples was studied and reliability of the obtained critical exponents was checked using scaling hypothesis. The critical exponents deduced in this study were observed to follow the mean field, 3D Ising and 3D Heisenberg model.