Half-metallicity and wandering axis ferromagnetism in Fe$_2$Ti$_{1-x}$Mn$_x$Sn (0 $< x \leq$ 0.3) Heusler Alloys

Abstract

We investigate the effect of Mn substitution in Fe$_2$Ti$_{1-x}$Mn$_x$Sn on electronic structure and magnetic and electrical transport properties. The spin-polarized density of states calculations using density-functional theory (DFT) yields a half-metallic ground state in Mn-rich compositions. Localized magnetic moments at Mn sites interacting through the cloud of conduction electrons formed by Fe and Ti atoms are also predicted. Electrical resistivity and magneto-transport measurements reveal a Kondo-like ground state at low temperatures and a peculiar linear negative temperature coefficient of resistance in the high-temperature regime with a predominant electron-phonon scattering mechanism. Analysis of room temperature powder X-ray diffraction data reveals a highly ordered L2$_1$ structure and reduction of antisite disorder upon Mn substitution. The temperature-dependent magnetization measurements reveal distinct features indicative of weak anisotropy in the system. Isothermal magnetization measured as a function of the applied field helps identify the unique magnetic ground state of the half-metallic Fe$_2$Ti$_{1-x}$Mn$_x$Sn composition as a ferromagnet with a wandering axis that distinctively orients in the direction of the applied magnetic field. The measurement of X-ray absorption fine structure (XAFS) reveals that the random anisotropy arises due to the local lattice distortion around Mn atoms in the prepared compositions. Our findings thus provide a new perspective for studying the mechanism of half-metallicity and associated magnetic order in Heuslers.