Static and dynamic characteristics of the Cr3+ EPR spectra in the Van Vleck paramagnet TmAl3(BO3)4

The advanced study of Cr³⁺ impurity ions in the Van Vleck paramagnet TmAl₃(BO₃)₄ is reported in this work. The angular dependence of the electron paramagnetic resonance spectrum from Cr³⁺ ion has been studied in detail, and the parameters of spin Hamiltonian were evaluated at T = 11 K [g = 1.980 ± 0.002; D = (−0.534 ± 0.001) cm⁻¹; E = (0.027 ± 0.005) cm⁻¹]. It was shown that the Cr³⁺ ions substitute trivalent aluminum ions and form a system of three magnetic equivalent ions rotated through 120° relative to each other. The deviation of the Z-axis from the C₃-axis for Cr³⁺ ions was found to be 2.5°. A significant temperature dependence of g and D parameters has been found. It was shown that a strong broadening of the EPR lines depends on the dipole and exchange fields generated by the magnetic moment of the thulium ion. The contributions of the excited states of the Tm³⁺ ion to the temperature-dependent component of the Cr³⁺ EPR linewidth have been discussed.