Neel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions
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In a recent article,1 a wide variety of phase transitions, with transition (t) temperature Tt , were shown to be usefully characterized by the form kBTt = Echar exp(-1/|| where || measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Nel temperature TN. It is first argued that the characteristic energy Echar can be usefully represented by k B, where 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 /TN is certainly greater than unity, the fifth having the ratio as unity to within experimental error. || 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.