Exploring the Structural and Magnetic Properties of Cu-Rich CuxMn3−xO4 Spinels for Advanced Magnetic Refrigeration at Liquid Nitrogen Temperatures

Abstract

Cu–Mn oxide spinels reveal notorious magnetocaloric performance at liquid nitrogen temperatures. We applied the soft chemistry sol–gel method to prepare Cu _x Mn _{3− x} O ₄ samples with nominal Cu content of x = 1, 1.5, 1.8, and 2. According to powder X-ray diffraction studies, we succeeded to fabricate multiphase samples with a high content of Cu in spinel phases. We provide insights into the structural and magnetic, as well as magnetocaloric, properties of the synthesized samples. We determine that in contrast to samples with x = 1.0 and 1.5, which are coupled ferromagnetically, the samples with x = 1.8 and 2.0 reveal ferrimagnetic coupling. The transition temperature is found to decrease only slightly from 78 K ( x = 1) to 75 K ( x = 2). The maximum values of the magnetic entropy change and relative cooling power are determined for each compound and found to be the largest for the sample with x = 1.0 due to its largest magnetization. Independent of the Cu content, here, the studied samples reveal a relative cooling power of larger than 139 J/kg, which highlights the relevance of these materials for magnetic refrigeration applications, particularly at liquid nitrogen temperatures.