Monte Carlo simulations of the magnetic behavior of diluted hexaferrites

The hexagonal ferrites BaFe₁₂O₁₉, SrFe₁₂O₁₉ and PbFe₁₂O₁₉ are ferrimagnets with Neel temperatures of approximately 720K. They also show interesting ferrolectric properties. By randomly substituting Ga ions for the Fe ions, the Neel temperature can be suppressed to zero. Recent experiments [1] have found the phase boundary to vary as T_N ∼ (1 - x/x_c)^2/3 over a wide x range, with x_c very close to the percolation threshold of the iron spins. We report the results of large-scale Monte Carlo simulations to explain this unusual phase boundary as well as the properties of the zero-temperature phase transition.
[1] S.E. Rowley at al., Phys. Rev. B 96, 020407(R) (2017)