Realization of tetragonal Heusler alloy Mn3-xCrxGa for spintronic applications

Abstract

Tetragonal Heusler alloys with high coercivity field (HC), low saturation magnetic moment and high Curie temperature (TC) have been considered as promising candidates for spin transfer torque (STT) applications. In this paper, tetragonal Heusler alloys Mn3-xCrxGa have been designed and realized in experiments by adjusting the ratio of Mn/Cr and selecting suitable heat treatment conditions. It has been found that Mn3-xCrxGa (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6 and 1) alloys exhibited multiple phase structures. As x > 0.5, both as-spun and as-annealed ribbons show pure B2-type body-centered cubic (b.c.c.) structure. The D022-type tetragonal Heusler structure starts to appear in the matrix of cubic B2 structure as x = 0.5 in as-annealed ribbon samples, and gradually develops to pure tetragonal structure as x = 0.3. There is a significant structure difference between as-annealed and as-spun ribbons as x ≤ 0.2. Cu3Au-type face-centered cubic (f.c.c.) structure is observed for as-spun ribbons, while the annealed ribbons show pure tetragonal structure. The pure tetragonal Heusler alloys have hard-ferrimagnetic properties with Hc higher than 258 kA/m, accompanied by a high TC, large magnetic remanence (Br) and low magnetic moment at room temperature, which are important factors for spin-transfer torque applications. Our work reveals the tunability of the magnetic and structural properties of Heusler alloys by changing the ratio of doping elements, providing a guidance for further searching for tetragonal Heusler alloys.