Weak ferromagnetism in hexagonal Mn3Z alloys (Z=Sn,Ge,Ga)

Abstract

We present combined spin model and first principles electronic structure calculations to study the weak ferromagnetism in bulk Mn 3 Z (Z=Sn, Ge, Ga) compounds. The spin model parameters were determined from a spin-cluster expansion technique based on the relativistic disordered local moment formalism implemented in the screened Korringa-Kohn-Rostoker method. We describe the magnetic ground state of the system within a three-sublattice model and investigate the formation of the weak ferromagnetic states in terms of the relevant model parameters. First, we give a group-theoretical argument how the point-group symmetry of the lattice leads to the formation of weak ferromagnetic states. Then we study the ground states of the classical spin model and derive analytical expressions for the weak ferromagnetic distortions by recovering the main results of the group-theoretical analysis. As a third approach we obtain the weak ferromagnetic ground states from self-consistent density functional calculations and compare our results with previous first principles calculations and with available experimental data. In particular, we demonstrate that the orbital moments follow a decomposition predicted by group theory. For a deeper understanding of the formation of weak ferromagnetism we selectively trace the effect of the spin-orbit coupling at the Mn and Z sites. In addition, for the case of Mn 3 Ga, we gain information on the role of the induced moment of Ga from constrained local density functional calculations.

Ground-state magnetic structure of Mn3Ge

“…Naturally, it is of interest to understand how such a large AHE can occur in an antiferromagnet, and there has been a spate of theoretical studies [2,[10][11][12][13][14][15][16][17][18]. The symmetries of noncollinear antiferromagnets generically do not forbid the AHE, and several of the recent studies have concluded that the particular chiral pattern of Mn spins can lead to large Berry curvature at the Fermi surface and thus a large AHE, as predicted by an earlier work [19].…”

Spin-Torque-driven Terahertz Auto Oscillations in Non-Collinear Coplanar Antiferromagnets

“…Recently, thin-films with different thickness ranging from 1 nm to 5 nm of both these materials have been grown using UHV magnetron sputtering [88][89][90][91]. In addition, different values of damping constants have been reported for Mn 3 Sn [56,77]. Therefore, we expect the results presented in Sections III C, IV and V to be useful for benchmarking THz dynamics in experimental set-ups with such thin films metallic antiferromagnets.…”

Magnetic properties of hematite revealed by an ab initio parameterized spin model

“…We then used the Spin-Cluster Expansion ( ) to extract spin model parameters from the state by mapping the adiabatic energy surface of the fluctuating state onto a Heisenberg model [17,18]. This method has been used successfully to describe -interfaces such as exchange bias systems [18,19], as well as bulk noncollinear antiferromagnets [20,21].…”