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EPR spectra of impurity Ho3+ ions in oriented SrY2O4 single-crystals are registered at the temperature 4.2 K in the frequency range from 70 to 180 GHz. The results of measurements evidence for the substitution of Ho3+ ions for the Y3+ ions at the structurally nonequivalent sites R1 and R2 with the local Cs point symmetry. The values of g-factors, hyperfine structure constants and the energy gaps between the ground and the first excited non-degenherate crystal-field sublevels of the ground 5I8 multiplet are determined. The observed specific features of the ground states of Ho3+ ions (non-Kramers doublets with the zero-field splittings of 4.30 and 1.67 cm–1) open a possibility to identify transitions in optical spectra of SrY2O4:Ho and inelastic neutron scattering spectra of SrHo2O4 crystals. [ABSTRACT FROM AUTHOR]

Low-temperature electron paramagnetic resonance measurements are performed on single crystals of LiY1 ‒xGdxF4 with low and moderate concentration of Gd ions. Modeling of the experimental spectra allows us to precisely determine microscopic parameters of the spin Hamiltonian of the parent LiGdF4 material, including the nearest-neighbor exchange constant. The obtained parameters are further tested by comparing a strongly anisotropic Curie–Weiss temperature obtained for LiGdF4 in our static magnetization measurements with theoretically computed values. We find a fine balance between principal magnetic interactions in LiGdF4, which results in a hidden magnetic frustration presumably leading to a delayed magnetic ordering and an enhanced magnetocaloric effect at low temperatures. [ABSTRACT FROM AUTHOR]