Systematics of EPR spectra of Gd3+ in rare-earth trinitrate hexahydrate hosts

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Abstract
Electron paramagnetic resonance spectra of the Gd3+ ion in various rare‐earth trinitrate hexahydrate (RNH) hosts have been studied at different temperatures. The values of the parameters are computed using a rigorous least‐squares fitting procedure in which all the resonant line positions obtained for various orientions of the external magnetic field are fitted simultaneously. While the room‐temperature results (in the hosts characterized by La, Ce, Pr, Nd, Sm, Dy, Er, Yb, and Y) are used to study the systematics exhibited by the zero‐field splitting parameters b20 and b22, the liquid nitrogen and liquid helium temperature results (in the hosts characterized by La, Pr, and Sm) have been used to deduce the absolute signs of the parameters, as well as the temperature variation of the parameters b20 and b22. It is found that, within experimental error, the values of b20 and of b22 are the same for those hosts R(NO3)3⋅6H2O for which R=Pr, Nd, Sm,Dy,Y, and Er; these values of b20 and b22 are close to those for the Yb(NO3)3⋅6H2O host, but are significantly different for those for the La(NO3)3⋅6H2O and Ce(NO3)3⋅6H2O hosts. The sign of b20 is found to be negative for all the hosts investigated at liquid helium temperature. A comparison is presented of the systematics of the spin Hamiltonian parameters for the RNH hosts with those for other hydrated rare‐earth hosts. It is found, contrary to the behavior in other hosts, that the parameter b20 does not exhibit a linear dependence upon the host rare‐earth ion radius.