Asymmetric ferromagnetic criticality in pyrochlore ferromagnet Lu2V2O7

Abstract

We study the ferromagnetic criticality of the pyrochlore magnet Lu 2 V 2 O 7 at the ferromagnetic transition T C % 70 K from the isotherms of magnetization MðHÞ via an iteration process and the Kouvel-Fisher method. The critical exponents associated with the transition are determined: b = 0.32(1), c = 1.41(1), and d ¼ 5:38. The validity of these critical exponents is further verified by scaling all the MðHÞ data in the vicinity of T C onto two universal curves in the plot of M=jej b versus H=jej bþc , where e ¼ T=T C À 1. The obtained b and c 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 Lu 2 V 2 O 7 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.

Negative thermal expansion and itinerant ferromagnetism in Mn$_{1.4}$Fe$_{3.6}$Si$_{3}$

“…These values of ex-ponents are identical to the other compositions in the Mn 1+x Fe 4−x Si 3 series and do not fall under any conventional universality class [26]. Similar unconventional critical behavior has also been observed in various ferromagnets [39][40][41][42][43][44]. Typically, in a short-range model, the exchange interaction J(r) decays rapidly with distance r as J(r) ∼ e −r/ξ .…”