Effect of Monoclinic Symmetry on the EPR Spectra of Gd3+‐Doped Hydrated Single Crystals of Rare‐Earth Trichlorides

Room‐temperature X‐band EPR data for Gd3+‐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 C2 parallel to the magnetic axes X, Y, and Z is provided. It is found that for, C2 ∥︁ Y, a significantly lower value of χ2, 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 and b , as functions of the host–ion radius, are also studied.