On the Ordering Effect of Antiferromagnetism

It is shown with the Heisenberg model that in general the Curie temperature of antiferromagnetism depends on the external field. It is also predicted that when an antiferromagnetic crystal with face-centered cubic or close-packed hexagonal magnetic lattice is kept at sufficiently low temperatures, its neutron diffraction pattern should show a transition from that due to an order of the $\alpha \beta$-type to that of the $\alpha {\beta }_3$-type as the applied field is greatly increased. When the Ising model is assumed, a quasichemical statistical theory shows that a latent heat and sudden disappearance of the neutron diffraction pattern should be observed in the antiferromagnetic transition of a face-centered cubic magnetic lattice. However, this cannot be predicted with assurance, since the Ising model is not reliable.