Correlation of quenched structural disorder and magnetism inTiFe2Laves-phase thin films

Abstract

In recent bandstructure calculations for the $C14$ Laves-phase intermetallic compound ${\mathrm{TiFe}}_{2}$ two energetically nearly degenerate magnetic ground states (antiferromagnetic and ferromagnetic) were predicted. As a consequence of this near-degeneracy in the $C14$ stability range of ${\mathrm{Ti}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}x}$ $(x\ensuremath{\approx}1/3)$ the magnetic properties are strongly correlated with the sublattices' occupation by Ti and Fe. We analyzed the magnetic properties of a series of thin epitaxial films with varying composition in the $C14$ stability range. The temperature- and field-dependent magnetic properties of these samples were determined by dc superconducting quantum interference device magnetization measurements. We found clear indications of magnetic phase separation into antiferromagnetic and ferromagnetic regions as a function of the composition. From the characteristic ordering temperatures a magnetic phase diagram for thin films in small aligning fields was established. Monte Carlo simulations based on a quenched random disorder model were performed. The resulting magnetization curves and the deduced simulated magnetic phase diagram are in good correspondence with the experimental data. We conclude that magnetic phase separation is a salient feature of ${\mathrm{Ti}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}x}$ $(x\ensuremath{\approx}1/3).$ It is induced by sublattice disorder which leads to a symmetry break of the exchange field and thus favors ferromagnetic spin alignment of the unit cell.