Neutron scattering study of spin waves in the antiferromagnet RbMnCl3

Abstract
The magnetic structure of the antiferromagnet RbMnCl3 (TN = 94K) consists of ferromagnetic planes stacked in the sequence A(+), B1(−), B1(+), A(−), B2(+), B2(−) along the C‐axis. The two kinds of sites, A and B for the Mn2+ ions contain respectively, ’’lone spins’’ and (much closer) spin pairs. This study of the spin wave spectrum was undertaken with the objective of determining whether the principal magnetic interactions JAB and JBB are of the same order of magnitude (conventional Heisenberg type) or whether a strong coupling model (JBB≳≳JAB) applies. Two distinct optic branches observed in the [qoo] direction immediately ruled out the strong coupling model. A fit to the data was then performed using the conventional spin wave model with excellent results. We find JBB/JAB = 1.65 (±.1). With spin values SA = 2.4 and SB = 2.5, JBB = 0.73 meV and JAB = 0.44 meV.

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