Electron spin resonance in ternary intermetallic compounds with MgAgAs structure

The authors have observed the (X-band) electron spin resonance in the equiatomic intermetallic compounds XPtSn, XRhSb and XNiSn, where X=U, Th, Hf, Zr, and Ti. These compounds crystallise in the cubic MgAgAs-type structure and exhibit a semiconducting behaviour in the electrical resistivity at higher temperatures. The ESR lineshapes in bulk samples is of the Dysonian form with an A/B ratio larger than three, which is characteristic of conduction electron spin resonance (CESR). In powdered samples the Dysonian lineshape and the A/B ratio depend on the ratio of sample diameter to the skin depth. The g-values are close to the free-electron value (g=2.0023) except for the U compounds which show both a large g-shift and linewidth. The effective spin density was mostly found to be of the order of 1020 cm-3 at room temperature as measured by comparing the intensity of the ESR signal with that of a known amount of DPPH. The ESR signal of Gd doped into the Hf and U compounds was clearly observed at temperatures where no signal could be found in the pure host materials. Here a negative residual linewidth was found in UPtSn, while the other compounds with Gd obeyed the normal Korringa relation ( Delta H=aT+b) with small thermal broadening and negative g-shift in HfPtSn and positive shift in URhSb.