Exploring the evolution of high-spin Co+2 and overall ferromagnetism in high-entropy oxide perovskite thin films

Our recent experiments on high-entropy oxide perovskite (HEOP) thin films revealed a drastic dependence of high-spin Co+2 (Figure 1 and Figure 2, for comparisons of Tb- and Lu- based HEOP thin films) and overall magnetism on substitutions at the rare-earth ion sites. Therefore, the goal of this project is to achieve a full understanding of how concentrations of high-spin Co+2 and the connected ferromagnetism evolve in rare-earth-based R(Co0.2Mn0.2Fe0.2Cr0.2Ni0.2)O3 [R: rare-earth ion] high-entropy oxide perovskite thin films. On one hand, we aim to track this evolution as function of rare-earth ion selections, in addition to stoichiometric variations within the transition metal block. Using state-of-the-art pulsed laser deposition, we will deposit high-quality R(Co0.2Mn0.2Fe0.2Cr0.2Ni0.2)O3 thin films on 001-oriented SrTiO3 (STO) substrates. Following fabrication, these thin films are planned to undergo full-scale temperature-dependent x-ray absorption spectroscopy (XAS) study, employing both x-ray magnetic circular dichroism (XMCD) and x-ray linear dichroism (XLD) at the L2,3 absorption edges of all involved transition metal elements. Furthermore, XMCD hysteresis loops with magnetic fields applied both out-of-plane (OOP) and at a grazing angle of 30° C will be recorded, to monitor the evolution of the ferromagnetic response, as a result of Co+2 concentration variations.