Effects of nonuniform vacancy distribution on diluted hexaferrites.

Recent experiments [1] on the diluted hexaferrite PbFe_12-xGa_xO₁₉ have demonstrated that the magnetic ordering temperature T_c vanishes as T_c~(x_c-x)^2/3 with increasing Ga concentration x. The critical concentration x_c agrees well with the percolation threshold of the underlying lattice. However, Monte Carlo simulations of a randomly diluted Heisenberg model [2] were unable to reproduce the experimentally observed 2/3-power law. Here, we explore whether unequal occupations by Ga atoms of the five distinct Fe sublattices in the hexaferrite crystal structure can explain the experiments. To this end, we perform extensive Monte Carlo simulations of Heisenberg models on hexaferrite lattices with nonuniform dilution.

[1] S.E. Rowley et al., Phys. Rev. 96, 020407 (2017)

[2] G. Khairnar et al., Eur. Phys. J. B 94, 43 (2021)