Effect of Monoclinic Symmetry on the EPR Spectra of Gd 3+ ‐Doped Hydrated Single Crystals of Rare‐Earth Trichlorides

Room‐temperature X‐band EPR data for Gd 3+ ‐doped isostructural rare‐earth trichloride hexahydrates are analyzed using a rigorous least‐squares‐fitting procedure. Discussion of the three forms of spin Hamiltonian corresponding to the orientations of the two‐fold monoclinic symmetry axis C 2 parallel to the magnetic axes X , Y , and Z is provided. It is found that for, C 2 ∥ Y , a significantly lower value of χ 2 , representing the goodness of fit, is obtained. A discussion of the determination of degree of monoclinicity, as revealed by the spin Hamiltonian parameters, is provided. Systematics of the spin Hamiltonian parameters b   2 0and b   2 2 , as functions of the host–ion radius, are also studied.