Volume dependence of magnetism in Mn-Fe: A fixed-spin-moment study

A spin-polarized, self-consistent total-energy linear muffin-tin orbital method and the fixed-spin-moment procedure were used to study theoretically the volume dependence of the magnetic properties of MnFe in the AuCu-I crystallographic structure. No constraints other than collinearity were imposed on the type of magnetic ordering in the four-atom unit cell. The antiferromagnetic ground state of the ordered ${\mathrm{Mn}}_2$ ${\mathrm{Fe}}_2$ phase with Mn magnetic moment of 1.15${\mathrm{\mu }}_{\mathit{B}}$ and no Fe moment was found. The Mn moments are shown to be very stable whereas the Fe moments are strongly sensitive to volume variation. Using two mutations of the fixed-spin-moment procedure, the energies required to change the type of magnetic ordering and to quench the magnetic moments are estimated. It is shown that for the experimentally relevant atomic volumes the energy necessary to destabilize the Fe magnetic moments is much smaller than the spin-flip energy. It is suggested that this feature is typical for all Invar systems.