Fermi level spin polarization of polycrystalline thulium by point contact Andreev reflection spectroscopy

Abstract

The spin polarization near the Fermi level in bulk polycrystalline ferrimagnetic thulium is investigated by means of point contact Andreev reflection (PCAR), in the temperature interval (1.9?9.2 K). The highest polarization measured is P ? 0.41(8), with barrier parameter Z ? 0.39(8), proximity region gap of D 1 ? 1.26(5) meV and an elevation of the electronic temperature of D T e ? 3.3(8) K, for a lattice temperature of T ? 2.20(5) K, and a contact conductance of G ? 330(5) G 0 . Both polarization and barrier power are found to be constant within the experimental uncertainties in the entire accessible temperature interval and linearly independent, while the proximity gap was found to obey the standard BCS temperature dependence with a T cGap ? 10.2(2) K, higher than the T cGap ? 9.2 K of bulk niobium. Despite its low ordering temperature, thulium could be suitable candidate for low critical current spin-transfer-torque demonstrations.