Mössbauer Spectroscopy of PdH¯ Fe Alloys

Abstract

Large changes in the electron susceptibility of PdH alloys have been observed with increasing H concentration, with important consequences for the magnetic and superconducting properties of these alloys. (1) To observe the effect of the changing spin susceptibility, we have studied PdH Fe alloys with 2, 1 and < 0.1 at. % Fe by Mössbauer spectroscopy in external magnetic fields. Mydosh(2) has reported spin glass behavior in the high Fe concentration alloys and Kondo phenomena in the dilute Fe alloys. For hydrogen‐metal ratios < 0.5, α and β phases, with low and high hydrogen content respectively, coexist. For temperatures below Tc of the α phase but above Tc of the β phase, we observe a superposition of a six line spectrum and a single line corresponding to the α and β phases respectively. (3) In an applied field, the β phase magnetizes and both phases have hyperfine fields which extrapolate to the same saturation value (Hhfs = −308 kOe for 1% Fe). For H/metal ratios > 0. 5, only the β phase is present and slightly lower Hhfs values are obtained. These results indicate that hydrogenation of FePd¯ alloys has little effect on the iron moment but has a marked effect on the polarization of the Pd spins and consequently on the coupling between spins. The low Fe concentration samples were studied as Co57 in Pd sources. For a 10 mCi source (∼0.1 % Fe in Pd) with H/Pd > 0.5, a Brillouin function with parameters J = 2.5, g = 2 and Hhfs = −300 kOe gave the best fit to the data. The hyperfine field is the same obtained in the nonhydrogenated case. For a 1 mCi source (∼0.01% Fe in Pd) with H/Pd, lower moments and hyperfine fields are observed suggesting Kondo quenching of the moment. These results suggest competition between Kondo and exchange effects in determining the Fe moment in dilute alloys.