Co magnetism and the order of the magnetic transition in Er1−xGdxCo2 Laves phases

Abstract

Co itinerant magnetism and the order of the magnetic transition in Er1−xGdxCo2 cubic Laves phases have been studied by magnetic measurements and a first principle density functional theory (DFT) calculation. The saturation magnetization (at 5K), derived from M−1∕H plot with a maximum field of 6T, decreases almost linearly with increasing Gd content. The derived Co magnetic moments, however, remain almost unchanged and range from 1.0to1.1μB∕Co. The first order magnetic transition at TC persists for x⩽0.1, as evidenced by thermomagnetic curves, M(T), and Arrott plots around TC. The total energy, Et, and magnetic moments are calculated as a function of lattice constant, a. In ErCo2, Et(a) shows two minima, corresponding to a low and a high spin state of Co, respectively. The Co sublattice is at a metastable high spin ferromagnetic state in ErCo2, which is responsible for the first order magnetic transition at TC. The replacement of Er by Gd eliminates the double minimum feature of Et(a) and drives the magnetic state of the Co sublattice to a stable state. The DFT calculation successfully explains the change in the order of the magnetic transition when the Gd content is increased in Er1−xGdxCo2.