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Temperature-dependent crystal field and hyperfine interactions

par Walsh, Walter W.M.;Jeener, Jean ;Bloembergen, N.
Référence Physical Review, 139, 4A, page (A1338-A1350)
Publication Publié, 1965

Article révisé par les pairs

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Résumé :

The effects of temperature variation on the spin-Hamiltonian parameters of several paramagnetic ions bound in simple crystals have been measured by magnetic-resonance techniques. Whenever possible the data have been analyzed for implicit (thermal-expansion) and explicit (lattice-vibration) temperature dependences using isothermal volume dependences determined in earlier hydrostatic-pressure experiments. In MgO the g shifts of two F-state ions, V2+ and Cr3+, increase and the cubic-field splittings of two S-state ions, Mn2+ and Fe3+, decrease with increasing temperature almost exactly as would be expected from thermal expansion alone. The axial crystalline-field splitting of locally compensated Cr3+ ions also increases with temperature at a rate attributable primarily to thermal expansion. The absence of appreciable explicit temperature dependence of crystalline-field parameters in MgO is consistent with an effective point-charge model for the source of the lattice potential and cubically symmetric lattice vibrations. In zinc blende, however, the cubic-field splitting of Mn2+ decreases more rapidly with rising temperature than may be accounted for by thermal expansion alone, presumably because of failure of the point-charge approximation. The hyperfine couplings of (V51)2+ and (Mn55)2+ in MgO decrease with increasing temperature, whereas a much smaller increase would be expected due to thermal expansion. Similar explicit variations of the (Mn55)2+ hyperfine interaction are found in ZnS, ZnO, CdTe, and KMgF3. The effect may be approximately represented by a power law of the form A(T)=A(0)(1-CTn) where n∼32. The significance of this result for nuclear-magnetic-resonance studies of concentrated magnetic materials is indicated. The general nature of the explicit temperature dependence is discussed but no detailed theoretical analysis is possible at this time. © 1965 The American Physical Society.