Determination of the Spin Polarization of Half-MetallicCrO2by Point Contact Andreev Reflection

Abstract

Andreev reflection at a Pb/CrO(2) point contact has been used to determine the spin polarization of single-crystal CrO(2) films made by chemical vapor deposition. The spin polarization is found to be 0.96 +/- 0.01, which confirms that CrO(2) is a half-metallic ferromagnet, as theoretically predicted.

Temperature dependence of transport spin polarization inNdNi5from point-contact Andreev reflection

“…The low T C of this material enables us to extract the transport spin polarization ͑P t ͒ all the way up to T C by carrying out the measurements using a finely cut superconducting Nb tip ͑su-perconducting transition temperature, T c = 9.2 K͒. The reproducibility of our results was confirmed by carrying out measurements on two different samples on NdNi 5 . In this paper we will primarily concentrate on the measurements carried out on one of these samples.…”

“…We have also shown that the superconducting quasiparticle lifetime extracted by fitting the PCAR spectra shows a minimum close to the ferromagnetic transition temperature of NdNi 5 . Through a detailed comparison with measurements carried out on the ferromagnet Fe and the nearly ferromagnetic compounds CaFe 4 Sb 12 and YbFe 4 Sb 12 , we attribute this decrease in the quasiparticle lifetime to the effect of large spin fluctuations close to the critical temperature of the ferromagnet.…”

“…It is known that ferromagnetic spin fluctuation in an s-wave superconductor increases the singlet-state repulsion. 33 Since ferromagnetic spin fluctuation in NdNi 5 is maximum at temperatures close to T C , it would be natural to attribute the decrease in the superconducting quasiparticle lifetime to the proximity of the superconductor to strong ferromagnetic spin fluctuation. In addition, we would like to note that at temperatures close to the superconducting transition temperature, additional broadening is likely to arise from the intrinsic decrease in the quasiparticle lifetime of the superconductor.…”

Andreev reflection spectroscopy of niobium point contacts in a magnetic field

“…These results have important implications for interpretation of transport spin polarisation measurements using PCAR technique. We demonstrate that stray magnetic fields can be responsible for the experimentally observed dependence of the spin polarisation on the strength of the interface barrier, and potential misassignment of the inferred spin polarisation.PACS Numbers: 74.45.+c; 75.50.Cc; The recent theoretical [1][2][3] and experimental [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] development of point-contact Andreev reflection (PCAR) spectroscopy is driven by the interest to find materials with high degree of spin polarization P. Such materials can be used for integration in spinbased microelectronics [19][20][21]. The technique may be used to determine the spatial variation of spinpolarised current in semiconductors [22,23].…”

Evidence for spin mixing in holmium thin film and crystal samples

“…3(a) and 3(b) respectively. The P-Z relationship of an S/F interface always takes a similar form in that high P is associated with low Z and vice versa and the origin of this dependence has been widely discussed in the literature [28][29][30][31][32] . The 'intrinsic' polarization is usually obtained by extrapolating a P-Z plot to low Z -although not usually to Z = 0 29 because Z also includes the effect of Fermi velocity mismatch between the S/F materials 33 .…”