A low-magnetic-field Raman heterodyne study of the Van Vleck paramagnet YAlO3:Eu3+

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Abstract
The hyperfine interaction of the Van Vleck paramagnet, trivalent europium (4f)6, dilute in YAlO3 host crystal is studied using Raman heterodyne spectroscopy in magnetic fields of 80 G in order to determine the directions of the quadrupole interaction in both the ground 7F0 state and the lowest 5D0 excited state. The measured magnetic resonance frequencies as a function of angle for the ground state agree with those frequencies calculated using previously published values of the nuclear Zeeman splitting factors. The excited-state magnetic field splitting factors are nearly isotropic as would be expected from the model of Elliott. Two magnetically inequivalent sites were observed. The NQR frequency against angle patterns demonstrate that the axes for the total quadrupole interaction for both states are identical within the precision of the experiment, with the three axes described by the normal to the mirror plane, and the axes of the pseudo-cell of the YAlO3 host. It is determined that the principal axes of the nuclear gN tensor coincide with those of the quadrupole tensor within ten degrees.