Study of Magnetic and Magnetotransport Properties of Epitaxial MnPtGa and Mn2Rh(1-x)Ir(x)Sn Heusler Thin Films

Manganese-based Heusler compounds display intriguing fundamental physical properties, determined by the delicate balance of magnetic interactions that give rise to real and reciprocal-space topology, sparking the interest in their potential application in the spin-based technology of the future. In this thesis, a thorough study of thin films of two Mn-based Heusler compounds, the hexagonal MnPtGa and inverse tetragonal Mn2Rh(1-x)Ir(x)Sn (0 < x < 0.4) system, was performed. The observation of Néel-type skyrmions in single-crystalline MnPtGa motivated our interest in the growth and characterization of thin films of this compound. The films were deposited by magnetron sputtering on (0001)-Al2O3 single crystalline substrates, achieving the epitaxial growth of the Ni2In-type hexagonal crystal structure (P6_3/mmc space group, no. 194). Two thermally-induced magnetic transitions were identified in MnPtGa thin films: below the ordering temperature (T_C=273 K) the system becomes ferromagnetic, followed by a spin-reorientation transition at T_sr=160 K, adopting a spin-canted magnetic structure. Resorting to single-crystal neutron diffraction (SCND), we were able to resolve the magnetic ground state of our MnPtGa thin films. The Mn magnetic moments were found to tilt 20 degrees away from the c-axis, forming a commensurate magnetic structure with a ferromagnetic component along the crystallographic c-axis and a staggered antiferromagnetic one in the basal plane. This further demonstrated the applicability of a bulk technique, such as SCND, to the study of magnetic structures in thin films. Additionally, the perpendicular magnetic anisotropy (PMA) in the system was determined by magnetometry technique. Electrical magnetotransport measurements were performed in a thickness series of MnPtGa thin films. A non-monotonous anomalous Hall conductivity (AHC) was observed, whose intrinsic Berry-curvature origin was elucidated by means of first-principle calculations. We further observed