Antiferromagnetic and Paramagnetic Resonance in CuF2·2H2O

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Abstract
Antiferromagnetic and paramagnetic resonance absorption has been measured in CuF2·2H2O. At 1.4°K, the antiferromagnetic resonances in zero field occur at 95.84±0.05 kMc and 95.91±0.05 kMc. The easy direction of magnetization occurs at an angle of 3.5° with the c axis. This orientation is in agreement with neutron diffraction and single‐crystal susceptibility measurements. Due to strong exchange narrowing, narrow paramagnetic resonance lines were observed. The g values are gξ=2.07, gη=2.08, and gζ=2.42. The principal axes are nearly coinciding with the ligand directions. From the g values, the energy levels and wave functions of the Cu++ ions are determined. A discussion of the anisotropy is given. The dipolar part is calculated numerically, and the anisotropic exchange of pseudodipolar type is determined, using the fact that ω1∼ω2 and the known easy magnetization direction. From the total anisotropy determined in this way, and the perpendicular susceptibility measured by Williams, the antiferromagnetic resonance frequency is predicted to occur at 130 kMc. The agreement with experiment is not unreasonable in view of the reduction of this frequency by the zero‐point oscillations of the spin waves. A brief discussion of the superexchange interaction in this crystal is given.

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