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 Δ1 = 1.26(5) meV and an elevation of the electronic temperature of ΔTe = 3.3(8) K, for a lattice temperature of T = 2.20(5) K, and a contact conductance of G = 330(5) G0. 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 TcGap = 10.2(2) K, higher than the TcGap = 9.2 K of bulk niobium. Despite its low ordering temperature, thulium could be suitable candidate for low critical current spin-transfer-torque demonstrations.

Magnetic, transport, and structural properties of SrRuO3 thin films

“…Magnetic field, of up to l 0 H ¼ 1 T, is applied in an arbitrary direction within the film plane, by a "Multimag" permanent-magnet-based variable-flux source. The construction of the PCAR setup and a description of the real-time derivative-spectrum measurement system used, and the spectral fitting software are can be found in references [6][7][8] and are omitted here. Fig.…”

Point contact Andreev reflection from semimetallic bismuth—The roles of the minority carriers and the large spin-orbit coupling

“…Here, polycrystalline Bi is investigated, utilizing the real-time Point Contact Andreev Reflection (PCAR) methodology, described elsewhere. 3 It is suggested that the same may be applicable to the characterisation of the electronic structure of other semimetals, such as graphite. The PCAR methodology has been extensively utilised for the evaluation of the Fermi level spin polarisation in magnetic metals.…”

“…8 and the real-time Differential Conductance Spectra (DCS) measurement system, and the spectral fitting software are all updated versions of the ones described previously. 3 The modelling of the conventional PCAR spectra is based on the wellknown modified BTK 9 theory, further taking into account superconducting proximity, electronic heating, modulation broadening, and series resistance. Least squares fitting of most of the experimental data is performed using fixed closed interval difference norm minimisation procedures, already described elsewhere.…”