Electronic and nuclear magnetism in PtFex at milli-, micro-, and nanokelvin temperatures

Nuclear magnetic resonance, AC susceptibility, and nuclear heat capacity of Pt samples with different concentrations of magnetic impurities x in the ppm range have been studied at magnetic fields (0 ± 0.05) mT ≤ B ≤ 248 mT and at temperatures 0.3 μK ≤ T ≤ 100 mK. Spin-lattice and spin-spin relaxation times of 195Pt strongly depend on the impurity content x, and the nuclear heat capacity data show enhanced values which scale with x at low polarization of the nuclear spin system. We present a model to describe the heat capacity data with a spatially varying internal field caused by the magnetic impurities. There is no indication for a nuclear magnetic ordering of 195Pt to a nuclear temperature of Tn = 0.3 μK and an electronic temperature of Tcl = 1.5 μK. (orig.)