Neel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions

In a recent article,1 a wide variety of phase transitions, with transition (t) temperature T-t, were shown to be usefully characterized by the form k(B)T(t) = E-char exp(-1/vertical bar lambda vertical bar) where vertical bar lambda vertical bar measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Neel temperature T-N. It is first argued that the characteristic energy E-char can be usefully represented by k(B)theta, where theta is the Curie-Weiss temperature. This assertion is then confronted with experimental data on four insulating transition metal oxides, these being selected as all having the paramagnetic ions on a facecentered cubic lattice. For four of the five theta/T-N is certainly greater than unity, the fifth having the ratio as unity to within experimental error. vertical bar lambda vertical bar is then argued to be related to physical parameters entering a mean field approximation to AFs. Finally, the above insulating Afs are complemented by a brief discussion of a metallic FeRh alloy where, in addition to having itinerant electrons and antiferromagnetism, elevating the temperature leads to a transition from an AF to a ferromagnetic state.