EPR spectra of Cr super(3+) ion in the Van Vleck paramagnet EuAl sub(3)(BO sub(3)) sub( 4)

We have presented new results on the EPR spectra and the ground state of the Cr super(3+) ion replacing Y super(3+) in YAl sub(3)(BO sub(3)) sub(4 ) and Eu super(3+) in EuAl sub(3)(BO sub(3)) sub( 4) single crystals. The EPR studies performed at frequencies of about 9.4 and 37GHz in a temperature range of 300-4.2K have revealed the peculiarities and differences of EPR spectra of Cr super(3+) ion as well as determined the spin-Hamiltonian parameters (g-factors, D, and E fine-structure parameters and their signs) in both crystals. The value and sign of the D parameter in both crystals are determined by both the nearest ligands around the Cr super(3+) ion and the spin-orbit interaction. The interaction between Cr super(3+) ion and rare-earth ion weakly influences on the ground-state splitting, while the changes of g-factors are mainly caused by the Cr super(3+) and Eu super(3+) ions interactions. The EPR spectra and contributions determining the value of spin-Hamiltonian parameters were analyzed on the basis of the superposition model of the crystal field.