Investigating the effects of B-site Cr doping on the structural, magnetic and magnetocaloric properties of La1.4Ca1.6Mn2− x Cr x O7 (0 ⩽ x ⩽ 0.4) bilayer manganites

Abstract

In this work, we describe the preparation of a series of Cr-substituted La1.4Ca1.6Mn2−x Cr x O7 (x = 0.0, 0.1, 0.2, 0.3, 0.4) double-layer perovskite compounds using a solid-state reaction method. The XRD patterns of all the samples are characterized by a tetragonal structure with a bilayer Ruddlesden–Popper phase. Scanning electron microscope micrographs of the doped samples display ambiguous granular variation and distribution, thereby establishing that the Cr content adversely influences the diffusion kinetics during the sintering process. Combined field-cooled moment vs temperature (M–T) and isothermal magnetization measurements establish the presence of a ferromagnetic to paramagnetic transition in all samples. Furthermore, the second-order nature of the transition is identified using the Arrott plots for these compounds. The maximum values of the change in isothermal entropy are found to be 2.98 J kgK−1, 2.39 J kgK−1, 1.48 J kgK−1, 1.29 J kgK−1, and 1.13 J kgK−1 for samples with x = 0.0, 0.1, 0.2, 0.3, and 0.4, respectively, when exposed to a field of 2.5 T. The entropy curves of the pristine sample are bounded within a narrow range of temperatures while the isothermal entropy curves are broadly expanded over a range of temperatures upon Cr-doping. The broad entropy profiles of the Cr-doped compounds versus temperature suggest a relatively high magnetocaloric potential, compared to the parent compound.