THE SCATTERING FUNCTION S(q,ω) OF RbMnF3

Abstract

The time-of-flight method has been used to measure S(q, w), the Fourier transformed spin correlation function, for the simple cubic antiferromagnet RbMnF3 at temperatures of 77 OK (0.93 TN) and at 97 OK (1.17 TN), over the full range of frequency and for values of q throughout the (110) plane. The Hamiltonian of RbMnF3 is known to be closely approximated by the nearest neighbour Heisenberg exchange model with an interaction J == 0.28 meV and S = 512. Using this Hamiltonian, S(q, w) has been calculated at each of the above temperatures by numericalsolutionof the dynamics of a 10 x 10 x 10 array of classical spins. Both the observed and calculated S(q, to) at 1.17 TX show appreciable structure, particularly for values of q near the antiferromagnetic phase zone boundary, which may be correlated with the spin wave peaks observed at 0.93 Tx. The decomposition of a triple-peaked spectrum, observed at one value of q, into distinct parallel and perpendicular peaks is shown to arise from the computed spin correlation functions.