Evidence for spin mixing in holmium thin film and crystal samples

In a number of recent experiments, holmium has been shown to promote spin-triplet pairing when in proximity to a spin-singlet superconductor.

PHYSICAL REVIEW B 83, 144518 (2011)

Evidence for spin mixing in holmium thin film and crystal samplesI. T. M. Usman, K. A. Yates, J. D. Moore, and K. Morrison; The Blackett Laboratory, Physics Department, Imperial College London, London SW7 2AZ, United Kingdom

V. K. Pecharsky and K. A. Gschneidner; Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, Iowa 50011-3020, USA

 T. Verhagen and J. Aarts; Kamerlingh Onnes Laboratory, Leiden Institute of Physics, P.O. Box 9504, 2300 RA Leiden, The Netherlands

 V. I. Zverev; Department of Physics, M.V. Lomonosov Moscow State University, Leninskie gory, Moscow, 119992, Russia

 J. W. A. Robinson, J. D. S. Witt, and M. G. Blamire; Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom

 L. F. Cohen; The Blackett Laboratory, Physics Department, Imperial College London, London SW7 2AZ, United Kingdom

(Received 27 January 2011; revised manuscript received 25 February 2011; published 21 April 2011)

In a number of recent experiments, holmium has been shown to promote spin-triplet pairing when in proximity to a spin-singlet superconductor. The condition for the support of spin-triplet pairing is that the ferromagnet should have an inhomogeneous magnetic state at the interface with the superconductor. Here we use Andreev reflection spectroscopy to study the properties of single ferromagnet/superconductor interfaces formed of holmium and niobium, as a function of the contact resistance of the junction between them. We find that both single-crystal and c-axis-oriented thin-film holmium show unusual behavior for low junction contact resistance, characteristic

of spin-mixing-type properties, which are thought necessary to underpin spin-triplet formation. We also explore whether this signature is observed when the junction is formed of Ni0.19Pd0.81 and niobium.

DOI: 10.1103/PhysRevB.83.144518 PACS number(s): 74.45.+c, 72.25.Mk, 75.70.−i, 74.50.+r