Effect of absorbed hydrogen on the magnetic properties of y(Fe 1− xMn x) 2 compounds

Abstract

Measurements of the magnetization and the Mössbauer effect were made on Y(Fe 1− x Mn x ) 2 compounds and their hydrides. All the compounds were found to absorb 3.7–4.0 hydrogen atoms per formula unit. The hydrogen absorption is accompanied by a large expansion of about 8% in the lattice constant without a change in the crystal structure of the cubic Laves phase (C15). The Curie temperature decreases linearly with x and ferromagnetism disappears at x = 0.7 for the host compounds. The Curie temperatures of the hydrides are nearly one-half those of the corresponding host compounds; the value of the Curie temperature decreases drastically beyond x = 0.2 and ferromagnetism disappears at x ≈ 0.4. The magnetic moment decreases linearly with x for the host compounds. Whereas the magnetic moment in each hydride is larger than that in the corresponding host compound for x ⩽ 0.2, beyond x = 0.2 it decreases rapidly with x. The hyperfine field of 57Fe is found to be significantly larger in the hydride phases than in the corresponding host compounds for x ⩽ 0.2, indicating that hydrogen absorption leads to an increase in the iron moment in this system. From the composition dependence of the hyperfine field and the magnetic moment, it seems likely that the magnetic moment of manganese atoms is enhanced by hydriding. The spin-glass-like magnetism observed in the hydrides with x ⩾ 0.4 is thought to originate with competing coupling tendencies between the magnetic atoms.