The temperature dependence of the resonance spectrum of [Cu(en)2H2O]SO4 single crystals is investigated in the temperature range 2.3–60 K at a frequency of ∼73 GHz. At a temperature T>15 K the angular dependence of the spectrum is described by a spin Hamiltonian of axial symmetry. At T<15 K a lowering of the symmetry to rhombic and a splitting the resonance line for a field orientation H∥b are observed. These effects are discussed in a model of two nonequivalent Jahn–Teller centers with intercoupled dynamic distortions in the cell. The low-temperature behavior of the resonance line is due to critical broadening in the region of short-range magnetic order.
The energy spectrum and resonance transitions in the EPR spectrum for a four-site cluster with an exchange interaction between nearest neighbors and diagonal coupling are calculated. The cases of isotropic and anisotropic exchange couplings are analyzed. The Dzyaloshinskii–Moriya interaction is taken into account in the second case. Using the computational results, it is possible to describe the shape of the EPR absorption band of a powdered sample of the metal organic compound CENI, which undergoes appreciable changes with a change in temperature. It is shown that these changes occur because of the appearance of additional interlevel resonance transitions, whose intensity increases as temperature decreases.
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