Point Contact Andreev Reflection (PCAR) is one of the few available methods for the determination of the Fermi level spin polarisation in metals and degenerate semiconductors. It has traditionally been applied at fixed (liquid He) temperatures, using pure niobium as the superconductor, and at essentially zero applied magnetic fields, all of which limit the amount of information that it can provide – i.e. do not allow for the extraction of the sign of the spin polarisation and make the assignment of the transport regime to ballistic or diffusive almost impossible.
Here a series of experiments is described, aimed at the expansion of this parameter space to higher magnetic fields and to higher temperatures. These require redesigned experimental setups and the use of higher performance superconductors. Demonstrations are described of the determination of the sign of the spin polarisation, at fields of more than 5 Tesla using a low-Z superconductor, as well as operations beyond 9.2 K. Doubts about the practical reliability of the PCAR technique are dispersed using systematic series of samples – the heavy rare-earths and comparisons with alternatives, such as spin-polarised field emission, photo-emission and Tedrow-Meservey tunnelling.
The specific material examples presented include 3d-metals, order-disorder transition alloys and zero-moment half-metals – Fe, FeAl and MnRuGa, alternative low-Z and high-Z superconductors – MgB2 and NbTi, and magnetic topological insulators, such as Cr- and V-doped (Bi1-xSbx)2Te3.
Plamen Stamenov and Kiril Borisov, "Point contact Andreev reflection and the measurement of spin polarization: high fields and novel materials
(Conference Presentation)," Proc. SPIE 9931, Spintronics IX, 993145 (Presented at SPIE Nanoscience + Engineering: September 01, 2016; Published: 4 November 2016); https://doi.org/10.1117/12.2238841.5167075282001.
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