Spin structures of europium selenide

Europium selenide undergoes a series of magnetic transitions among antiferromagnetic ($\uparrow \uparrow \downarrow \downarrow$ and $\uparrow \downarrow \uparrow \downarrow$) and ferrimagnetic ($\uparrow \uparrow \downarrow$) phases. We propose that these phases are stabilized by lattice distortions induced by the differential dependence of the two exchange constants on the interplane distance. The corresponding change in dipolar energy is computed and is shown to be relatively small. In the induced distortion neighboring planes of parallel spins converge, and neighboring planes of antiparallel spins diverge. This model predicts macroscopic dilatations in general agreement with data of Griessen, Landolt, and Ott. A molecular-field theory is given and the results and limitations of the theory are discussed.