Magnetic and transport properties of epitaxial Co2MnSi Heusler thin films with ultralow damping

This poster contribution was presented by Anna Maria Friedel at the 5th Ultrafast Magnetism Conference (UMC 2022) in Nancy, France. --- Abstract: Magnetic materials with low Gilbert damping are indispensable for future spintronic and magnonic applications. Half-metallic Co2Mn-Heusler compounds are promising candidates for such applications mainly due to their 100% spin polarisation at the Fermi level and the associated low Gilbert damping. Amongst them, Co2MnSi thin films are of particular interest combining high saturation magnetisation, high Curie temperature and ultralow Gilbert damping in the 10-4 range [1], when epitaxially grown with decent control over stoichiometry to ensure the desired L21 chemical ordering [2]. Yet, downscaling towards ultrathin films or microstructures is a critical necessity for applications and is known to impact the properties of magnetic materials. We report on the successful fabrication of epitaxial Co2MnSi thin films with maintained excellent properties for thicknesses in the range of 4 - 44 nm [3]. Predominant L21ordering was confirmed by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). After confirming the structural quality of the samples, the evolution of the magnetic and transport properties were investigated. Magnetisation dynamics were studied by ferromagnetic resonance (FMR) spectroscopy on the thin film samples. Low Gilbert damping values in the 10-4 to 10-3 range were found, reaching down to 7.8 x 10-4 for the 8 nm film. Transport properties were measured on Hall bars that were patterned out of the thin film samples. Longitudinal and transverse resistivity measurements were performed as a function of thickness and temperature. The upper part of the minority spin band gap was extracted from the temperature dependence of the resistivity and negative anisotropic magnetoresistance (AMR) ratios were obtained for the whole thickness series, all of which confirm the half-metallicity of all samples. In this study, a degradation of the Heusler thin films’ desired properties was only apparent for the film of 4 nm thickness, demonstrating that the excellent qualities of the Heusler thin films can be retained down to film thicknesses of 8 nm. References :[1] C. Guillemard, et al., Phys. Rev. Applied 11, 064009 (2019)[2] C. Guillemard, et al., J. Appl. Phys. 128, 241102 (2020)[3] C. de Melo, et al., Appl. Mater. Today 25, 101174 (2021)