Paper MI+2D-WeM12
Epitaxy of Novel Co_1.5Ti_0.5FeGe Heusler Alloy Thin Films

Wednesday, October 23, 2019, 11:40 am, Room A210

While the half-metallic ferromagnets are considered ideal candidates to be used for efficient spintronics devices, a single-phase microstructure with promising half-metallic character is recently reported in a bulk Co_1.5Ti_0.5FeGe Heusler alloy¹. This alloy has Ti substitution for Co atoms in the parent Co₂FeTiGe alloy, where the parent alloy does not exhibit half-metallic behavior². However, the Ti substitution is useful not only to stabilize single-phase behavior but also to tune half-metallicity by the Fermi level shift. In this work, successful growth of epitaxial thin films of this novel Co_1.5Ti_0.5FeGe alloy on a-plane sapphire and MgAl₂O₄(100) by using DC magnetron sputtering will be reported. In-situ reflection high energy electron diffraction shows that the films grow epitaxially with smooth surfaces. X-ray diffraction analysis confirms the epitaxial relation and lattice parameters within a few percent of the reported bulk value. Presence of finite size Laue oscillations in the XRD pattern and 0.035˚ full width at half maximum of rocking curve obtained in case of films grown on a-plane sapphire describe excellent quality of the films. The presence of superlattice peaks; (200) and (111), indicate a strong tendency to form the L2₁ structure. The degree of B2 ordering is estimated to be as high as 0.92 showing that intermixing between the atoms in the octahedral and tetrahedral sites is limited. Atomic force microscopy shows that the films grown on MgAl₂O₄(100) are atomically smooth with a rms roughness of 0.2 nm. Magnetic measurements of films grown at 800ºC show that the saturation magnetization is in close agreement with the bulk value. Angle-dependent magnetization measurements show the symmetry of the coercivity is consistent with a magnetocrystalline anisotropy. Temperature-dependent transport measurements show metallic behavior and an ordinary magnetoresistance as high as 1.55 % is obtained at 100 K. All the above results describe the feasibility of growing good quality epitaxial films of novel Co_1.5Ti_0.5FeGe alloy with the structural and magnetic properties consistent with reported bulk properties.

1. KC et al., Tunable Properties and Potential Half-Metallicity in (Co_2-xTi_x)FeGe Heusler Alloys; an Experimental and Theoretical Investigation, submitted to Phys. Rev. Materials.

2. Kumar et al., First-principles Calculation and Experimental Investigations on Full-Heusler Alloy Co₂FeGe, IEEE Transactions on Magnetics 45, 3997 (2009).