Seminars Archive

Structure and Properties of Quaternary and Tetragonal Heusler Compounds for Spintronics and Spin Transfer Torque Applications

Abstract
In addition to the well‐known cubic structures of Heusler compounds, tetragonally distorted Heusler compounds are currently receiving increased interest in the field of spintronics, especially for spin torque applications. Only few tetragonal distorted Heusler materials have been studied thoroughly, Mn3Ga and Mn3−xGa are the most prominent examples. These materials are particularly interesting due to the perpendicular magnetic anisotropy which can be achieved in thin films opening the door to spin‐torque devices. Therefore, it is essential to design new materials that fulfill the corresponding criteria, i.e. high spin polarization and Curie temperature but a low saturation magnetization and magnetic damping. Also quaternary Heusler compounds have wide range of possibilities for material design in the field of spintronics according to their large number of possible combinations of atoms. This work is focused on the electronic, magnetic, and structural properties of Mn2‐xRh1+xSn and Mn3−xCoxGa Heusler compounds and also three different series of quaternary Heusler compounds, XX′MnGa (X = Cu, Ni and X′ = Fe, Co), CoFeMnZ (Z = Al, Ga, Si, Ge), and Co2−xRhxMnZ (Z= Ga, Sn, Sb). These compounds are of exceptional importance due to their large diversity of adaptive magnetic properties and their tunability by variation of electron doping. In Mn2−xRh1+xSn series, Mn2RhSn crystallizes in the inverse tetragonal structure, shows a hard‐magnetic hysteresis loop and does not follow the Slater‐Pauling rule. With substituting Mn by Rh, the inverse cubic structure is observed. All cubic samples show perfect Slater‐Pauling behavior and a soft hysteresis loop. The Mn3−xCoxGa series, with X varying from 0.1 to 1.0 in steps of X = 0.1, were synthesized and investigated. It has been shown that the series Mn3−xCoxGa crystallize in the inverse tetragonal structure (I 4m2, space group no 119), for X= 0.1 − 0.4, in the cubic inverse Heusler CuHg2Ti structure type (space group no 216, F4 3m), for X = 0.6 − 1 and in both cubic and tetragonal phases for Mn2.5Co0.5Ga. In this series, while the tetragonal alloys are hard magnets and exhibit the features typically attractive for STT applications, the cubic systems are soft magnets and present the 100% spin polarized materials (or half‐metals) obeying the Slater‐Pauling rule. Different type of magnetic properties, hard‐magnetic properties for Mn‐rich alloys and softmagnetic hysteresis loops for Co‐rich alloys, facilitates the tenability of the magnetic anisotropy by varying the Co concentration. In quaternaries, predicted half‐metallic ferromagnets were synthesized and investigated to find new suitable candidates with high spin polarization, magnetic moment, and Curie temperature for spintronics applications.