Disorder effects in magnetic properties and electronic structure of orthorhombic Mn₂TiGe

Heusler alloys attract much attention due to their potential application in spintronic, magneto-optical and magnetocaloric devices [1-3]. In this work, we theoretically studied disorder effects in the electronic structure and magnetic properties of full Heusler Mn₂TiGe alloy, crystallized in the orthorhombic Ima2 structure within density functional theory (DFT). We calculated that Mn₂TiGe without defects exhibits metallic properties with a total magnetic value of 4.6 μ_B/f.u. and with partial magnetic moments of 3.2 μ_B/Mn, 1.3 μ_B/Ti and 0.1 μ_B/Ge. This value is higher than the value of 1.99 μ_B/f.u., reported recently from theoretical calculations for the L2₁ phase of Mn₂TiGe [4]. In our additional calculations for Mn2TiGe with the antisite defects Mn-Ge, the total magnetic moment was decreased to 1.3 μ_B/f.u. with 0.9 μ_B/Ti and a negligible Ge moment. An almost identically low value of the total moment 1.1 μ_B/f.u. was found in Mn₂TiGe with the antisite defects Mn-Ti; in this case, the partial moments gradually decreased. The largest effect on the magnetic moment is exhibited by the antisite change between Ti and Ge, because it provides further suppression of the Mn and Ti moments, causing the total magnetic moment to be equal to 0.6 μ_B/f.u. Also, in all cases, the Mn electronic states shift to lower energies, forming two peaks of states in the valence band in the electronic structure. Thus, we demonstrated that the investigated antisite disorder types result in a significant (by several times) reduction in the magnetic moment of the novel orthorhombic Mn₂TiGe alloy. This research was supported by the Russian Science Foundation, grant number RSF 22-42-02021.

[1] Phys. Rev. Mater. 3 (2019) 062401
[2] J. Magn. Magn. Mater. 398 (2016) 7
[3] J. Electron. Mater. 46 (2017) 2710
[4] J. Magn. Magn. Mater. 333 (2013) 162