Spin-density inversion symmetry driven first-order magnetic phase transition in GaCMn₃

The first-order magnetic phase transtion of the metallic perovskite GaCMn₃ has been investigated in terms of density-functional theory using the all-electron total-energy full-potential linearized augmented plane-wave method. We found that the antiferromagnet{c (AFM) state is more stable energetically than the ferromagnetic (FM) state at the low-temperature lattice constant. Total-energy calculations yield a critical lattice constant of 7.3411 a.u., which is remarkably close to the experimental one (7.34 a.u.) The calculated magnetic moments of Mn in each magnetic state are almost constant with lattice-constant variation, ∼1.58μ_B for the FM and ∼1.80μ_B for the AFM states, which are very close to experiment. The FM spin density is found to have even inversion symmetry, while the AFM one has odd, which restricts the direction of the AFM ordering vector along the [111] direction via tilting of the orbital orientation axis. Hence, the spin-density parity about the spin-inversion symmetry may be a key for understanding the first-order phase transition in GaCMn₃. We also found that the oddness of the spin-density-inversion symmetry in the AFM state brings about the wave-function sign dependent spin polarization and changes the bonding character. From the calculated density of states, the hybridization between the Ga-4p and Mn-3d states is important for determining the magnetism of GaCMn₃.