Temperature dependence of transport spin polarization in NdNi₅ from point-contact Andreev reflection

Abstract

We report a study in which point-contact Andreev reflection (PCAR) spectroscopy using a superconducting Nb tip has been carried out on NdNi₅, a ferromagnet with a Curie temperature of T_c∼7.7K. The measurements were performed over a temperature range of 2–9K, which spans across the ferromagnetic transition temperature. From an analysis of the spectra, we show that (i) the temperature dependence of the extracted value of transport spin polarization closely follows the temperature dependence of the spontaneous magnetization; (ii) the superconducting quasiparticle lifetime shows a large decrease close to the Curie temperature of the ferromagnet. We attribute the latter to the presence of strong ferromagnetic spin fluctuations in the ferromagnet close to the ferromagnetic transition temperature.