Six inequivalent Cu2+EPR spectra were observed at 4.2 K in single crystals of FeSiF6thinsp;sdot;thinsp;6H20. The estimated parametersgzsim;2.38 and thgr;sim;40deg;, where thgr; is the angle between the ioniczaxis and thecaxis, differ from those measured in crystals of similar structure. These differences have been explained in terms of an isotropic Cu2+ndash;Fe2+exchange HamiltonianJS1thinsp;sdot;thinsp;S2, withJ=+(0.030plusmn;0.003) cmminus;1, which gives a contributiongexsim;minus;5.05Jthinsp;sin2thinsp;thgr;, where thgr; is the angle between the external magnetic field and thezaxis. Perpendicular to thecaxis, an independent estimate of +0.034 cmminus;1forJwas made from the lowhyphen;field displacement of a satellite spectrum.
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