Abstract
The super-exchange interaction parametersI(Fe, Cr) of Fe3+ and Cr3+ in iron doped rate-earth orthochromitesRCr0.99Fe0.01 O3 (R=La, La0.5Nd0.5, Nd, Sm, Gd, Dy, Y, Er, Yb or Lu) have been obtained from57Fe magnetic hyperfine structure measurementsvia the Mossbauer effect. The dependence of the experimental valuesI(Fe, Cr) on the Fe−O−Cr average superexchange angle θ (depending upon the relative size of the rare-earth (RE) ionR 3+) is well described by the equationI(d5, d N ) = α N + β N cosθ + γ N cos2 θ. Within the accessible range of super-exchange angles 142°≲θ≲156°, the Fe3+−O2−−Cr3+ interaction is negative (antiferromagnetic). However, a theoretical analysis predicts a sign reversal forI(Fe, Cr.) at about θ ≈ 162° and thus ferromagnetic character of the interaction between 162° and 180°. The spin-only super-exchange interaction integrals fore g andt 2g electrons, separately, are also calculated. Their angular dependence is accounted for by the behaviour of the antiferromagnetic kinetic and ferromagnetic potential exchange which are of different character when passing from 180° to 90° super-exchange geometry. The magnitude and the sign of the spin-only super-exchange integral for an arbitrary 3d cation, pair is predicted.
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