Electron paramagnetic resonance ofGd3+in platinum

Abstract

We have observed the electron paramagnetic resonance (EPR) of ${\mathrm{Gd}}^{3+}$ in both polycrystalline and single-crystal samples of dilute Pt: Gd alloys. The polycrystalline samples display a single resonance line whose thermal broadening is concentration dependent. Fully resolved fine structure appropriate to ${\mathrm{Gd}}^{3+}$ in a cubic environment is obtained from the single-crystal samples. From these results a value for ${b}_{4}^{0}$ of +86 G is deduced, a value some three times larger than that found to date in any other cubic pure metals. It is shown conclusively that the experimental spectra from the single-crystal samples consist of the resolved single-ion fine-structure spectrum and an additional cluster line with the same $g$ value as the single-ion spectrum. For most directions in the {110} plane excellent agreement is obtained between the single-ion spectra and those simulated using the Barnes-Plefka motional-narrowing theory. The existence and behavior of the cluster line is qualitatively explained in terms of a cross-relaxation process. Finally it is shown that the excitation energy ${E}_{\ifmmode\pm\else\textpm\fi{}}$ for the process $4{f}^{7}\ensuremath{\rightarrow}4{f}^{8}$ as involved in EPR is not the same as measured by optical experiments such as x-ray photoemission spectroscopy. A theory which describes this is capable of explaining the experimental exchange and crystal-field parameters.