Electron paramagnetic resonance of Gd3+ in platinum

We have observed the electron paramagnetic resonance (EPR) of Gd3+ 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 Gd3+ in a cubic environment is obtained from the single-crystal samples. From these results a value for b40 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 for the process 4f74f8 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.