Experimental evidence of the Dzyaloshinsky-Moriya antisymmetric exchange interaction in the one-dimensional Heisenberg antiferromagnet KCuF3: EPR measurements

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Abstract
Based on the authors' results of EPR experiments, they point out that KCuF3, a one-dimensional Heisenberg antiferromagnet in spite of its pseudo-cubic crystal structure, has a Dzyaloshinsky-Moriya (DM) antisymmetric exchange interaction Sigma dijSi*Sj between spins on the c-axis; the direction of dij is perpendicular to the c-axis. The observed EPR linewidth shows (2+sin2 theta )-like angular behaviour ( theta is the angle between the c-axis and the external field), which coincides well with the theory of line broadening due to the DM interaction with dij perpendicular to c-axis. The linewidth shows a rapid decrease with lowering temperature and its value extrapolated to T=0 K from the paramagnetic region is zero. As the theory by Soos et al. (1977) shows, this temperature dependence also indicates that the EPR line is governed by the DM interaction; i.e. it arises from the four-spin correlation functions ((Sialpha Sjbeta -Sibeta Sjalpha )2) (where alpha and beta =x, y and z) in the second moment due to the DM interaction which is different from ((Sialpha Sjbeta +Sibeta Sjalpha )2) of the perturbation terms of both the dipole-dipole and the anisotropic exchange interactions.