Asymmetric ferromagnetic criticality in pyrochlore ferromagnet Lu₂V₂O₇

We study the ferromagnetic criticality of the pyrochlore magnet Lu₂V₂O₇ at the ferromagnetic transition T_C≈70K from the isotherms of magnetization M(H) via an iteration process and the Kouvel-Fisher method. The critical exponents associated with the transition are determined: β = 0.32(1), γ = 1.41(1), and δ=5.38. The validity of these critical exponents is further verified by scaling all the M(H) data in the vicinity of T_C onto two universal curves in the plot of M/|ε|^β versus H/|ε|^β+γ, where ε=T/T_C-1. The obtained β and γ values show asymmetric behaviors on the T<T_C and the T>T_C sides, and are consistent with the predicted values of 3D Ising and cubic universality classes, respectively. This makes Lu₂V₂O₇ a rare example in which the critical behaviors associated with a ferromagnetic transition belong to different universality classes. We describe the observed criticality from the Ginzburg-Landau theory with the quartic cubic anisotropy that microscopically originates from the anti-symmetric Dzyaloshinskii-Moriya interaction as revealed by recent magnon thermal Hall effect and theoretical investigations.