Upper Critical Fields in Nb/Ni Bilayers

POSTER

Abstract

We studied the upper critical fields ($H_{c2}$) of Nb/Ni bilayers. These bilayers had a constant Nb thickness of 33 nm, and the Ni thicknesses varied from 0-7 nm. For each sample, we took resistive measurements of the superconducting transition under fields ranging from 0-4360 G. From these measurements, we obtained the upper critical field slopes ($H_{c2}^\prime$) of each sample. The $H_{c2}^\prime$ of a simple Nb layer was 3710 G/K, while the $H_{c2}^\prime$ values for the bilayers ranged randomly from 4650-6840 G/K. While the critical temperatures ($T_c$) of the samples seemed to exhibit a particular non-monotonic pattern as a function of Ni thickness (due to proximity effect), the $H_{c2}^\prime$ values as a function of Ni thickness formed no such clear pattern. We also analyzed the curvature of the $H$ vs. $T_c$ plots for each sample. Most of the plots were linear at lower applied fields, but many showed either positive or negative curvature as we applied higher fields. This curvature began anywhere between 2000 and 4000 G. Generally, bilayers with thinner Ni layers produced $H$ vs. $T_c$ plots with negative curvature, and bilayers with thicker Ni layers produced plots with positive curvature.

Authors

  • Emily Davis

    Covenant College, Covenant College, Lookout Mtn, GA 30750

  • Chris Neu

    Florida State University, NHMFL, Institut Neel, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China, Florida State University, Department of Physics, Florida State University, Tallahassee, FL, Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, Florida State University, National High Magnetic Field Laboratory, Institute of Physics, Chinese Academy of Sciences, China, Austin Peay State University, University of Pardubice, Davidson College, Covenant College, Lookout Mtn, GA 30750, Russian Academy of Sciences, Moscow, RU, University of Tennessee Space Institute, Tullahoma, TN, USA, Sandia National Laboratories,* Albuquerque, NM, Arkansas State University, Jonesboro, AK, None, Mississippi State University, Mississippi State University Department of Physics and Astronomy, Florida State University and the National High Magnetic Field Laboratory, Faculte des Sciences et Techniques and Universite Aix-Marseille, MIT Haystack Observatory, Departments of Chemistry and Physics, University of Tennessee of Chattanooga, Departments of Chemistry and Physics, University of Tennessee at Chattanooga, Western Kentucky University, Thomas Jefferson National Accelerator Facility, Newport News, VA, Fermilab, University of Virginia and Fermilab, Indiana University Bloomington, Indiana University Health Proton Therapy Center, University of North Florida, National Superconducting Cyclotron Laboratory, Michigan State University, Flordia State University, Louisiana State University, Washington University, Argonne National Laboratory, Lawrence Berkeley National Laboratory, Department of Physics, Florida State University., JINR, Tsinghua University, LBNL, LBNL/Vanderbilt University, Vanderbilt University, Florida A\&M University, Georgia Institute of Technology, Department of Physics, Virginia Tech, Gatton Academy, Exeter University, Florida International University, Office of Research, University of North Florida, Physics Department, University of North Florida, NSCL, Michigan State University, Physics Department, Florida State University, University of Tennessee-Knoxville, Neel Institut, Kazan Federal University, Bielefeld University, Ben Gurion University, LCIB - CEA, University of Georgia, Lawrence Livermore National Laboratory, Livermore, CA 94550, NHMFL, Tallahassee, USA, Department of Chemistry, University of Waterloo, Ontario, Canada, NHMFL, Tallahassee FL 32310 USA, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany, Wigner Research Center for Physics, Budapest, Hungary, Experimental physics II, University of Augsburg, Germany, Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, National High Magnetic Field Laboratory Florida State University, Tallahassee, Florida 32310, IM2NP-CNRS (UMR 7334) and Universite Aix-Marseille, National High Magnetic Field Laboratory Applied Superconductivity Center, Heifei National Lab for Physical Science at Microscale, USTC, Institute of Physics, Chinese Academy of Sciences, Department of Electrical Engineering, Rice University, National High Magnetic Field Laboratory, National High Magnetic Field Laboratory/FSU, University of Virginia

  • Phillip Broussard

    Covenant College, Covenant College, Lookout Mtn, GA 30750