Epitaxial and stoichiometric effects on structural and chemical ordering in Heusler alloys

ORAL

Abstract

The Heusler alloys of Co$_{2}$MnGe and Co$_{2}$MnSi have been predicted to be half-metallic, where the minority spin density of states shows a gap at the Fermi Level. However, half-metallicity has not yet been realized owing to its expected sensitivity to atomic disorders associated with off-stoichiometry and epitaxial constraints. Combinatorial epitaxial films of Co$_{x}$Mn$_{y}$Ge$_{z}$ and Co$_{x}$Mn$_{y}$Si$_{z}$ have been grown on Ge (111) substrates in and around the Heusler stoichiometry using molecular beam epitaxy. The structural and chemical ordering of the films has been examined using synchrotron x-ray microbeam techniques, including x-ray diffraction and energy dependent anomalous diffraction. A comprehensive model has been developed for anomalous diffraction, allowing for detection and quantification of various disorders even at small amounts, including site-dependent vacancies and elemental site swapping. The x-ray experiments reveal that the ordering is very sensitive to the Co:Mn atomic ratio and that epitaxial strain can cause a shift in the composition of highest structural ordering away from the Heusler stoichiometry, accompanied by increased chemical disorders. These findings have made it possible to explore spin dependent states as a function of structural and chemical ordering.

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Authors

  • Brian A. Collins

    University of North Carolina at Chapel Hill

  • Jaetae Seo

    NC A\&T State University, Penn State University, The Ohio State University, Wright State University, AFRL/RYHC Hanscom AFB MA 01731, Harvard University, The College of William \& Mary, NCSU Near-field Optics Lab, University of North Carolina at Chapel Hill, Weizmann, PTB, Braunschweig, UMass, TUNL/Duke, UConn, UConn/TUNL, University of North Carolina, Chapel Hill, North Carolina State University, Brimrose Corporation of America, Hampton University, Elizabeth City State University, Department of Physics, Florida A\&M University, Tallahassee, Florida-32307, Department of Physics, University of Rajshahi, Rajshahi-6205, Bangladesh, Department of Physics, University of Rajshahi, Rajshah-6205, Bangladesh, Department of Physics, University of Rajshahi, Rajshahi-6250, Bangladesh, Department of Physics, University of Rajshahi-6205, Bangladesh, Alabama A\&M University, Fachbereich C-Mathematik und Naturwissen-Schaften, Bergische Universitat Wuppertal, D-42097, Wuppertal, Germany, NC State University, College of William and Mary, Department of Physics, N.C. State Univeristy, Research Triangle Institute, NCSU Physics, Pennsylvania State University, Tsinghua University, Lawrence Berkeley National Laboratory, Vanderbilt University, LSU, UNIRIB, U. Tenn., ORNL, Miss. St., University of North Carolina at Chapel Hill and Triangle Universities Nuclear Laboratory, NCA\&T, Duke, NCCU, UNC-Chapel Hill, Department of Physics, North Carolina State University, Department of Chemistry, North Carolina State University, Department of Physics and Astronomy, University of North Carolina, Chapel Hill, Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hil, North Carolina School of Science and Mathematics, Department of Physics, Elon University, Dept. of Physics - UNC - Chapel Hill, Nanyang Technological University, School of Materials Sciences and Engineering, Singapore, Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3255, USA, Argonne National Laboratory, Department of Physics, Hampton University, Hampton, VA 23668, Korea Research Institute of Standards and Science, Daejeon, 305-600, South Korea, Department of Chemistry, Gyeongsang National University, Jinju 660-701, South Korea, Electronics and Telecommunications Research Institute, Daejeon, 305-700, South Korea, Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, MA 01609

  • Frank Tsui

    University of North Carolina, University of North Carolina at Chapel Hill

  • Jaetae Seo

    NC A\&T State University, Penn State University, The Ohio State University, Wright State University, AFRL/RYHC Hanscom AFB MA 01731, Harvard University, The College of William \& Mary, NCSU Near-field Optics Lab, University of North Carolina at Chapel Hill, Weizmann, PTB, Braunschweig, UMass, TUNL/Duke, UConn, UConn/TUNL, University of North Carolina, Chapel Hill, North Carolina State University, Brimrose Corporation of America, Hampton University, Elizabeth City State University, Department of Physics, Florida A\&M University, Tallahassee, Florida-32307, Department of Physics, University of Rajshahi, Rajshahi-6205, Bangladesh, Department of Physics, University of Rajshahi, Rajshah-6205, Bangladesh, Department of Physics, University of Rajshahi, Rajshahi-6250, Bangladesh, Department of Physics, University of Rajshahi-6205, Bangladesh, Alabama A\&M University, Fachbereich C-Mathematik und Naturwissen-Schaften, Bergische Universitat Wuppertal, D-42097, Wuppertal, Germany, NC State University, College of William and Mary, Department of Physics, N.C. State Univeristy, Research Triangle Institute, NCSU Physics, Pennsylvania State University, Tsinghua University, Lawrence Berkeley National Laboratory, Vanderbilt University, LSU, UNIRIB, U. Tenn., ORNL, Miss. St., University of North Carolina at Chapel Hill and Triangle Universities Nuclear Laboratory, NCA\&T, Duke, NCCU, UNC-Chapel Hill, Department of Physics, North Carolina State University, Department of Chemistry, North Carolina State University, Department of Physics and Astronomy, University of North Carolina, Chapel Hill, Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hil, North Carolina School of Science and Mathematics, Department of Physics, Elon University, Dept. of Physics - UNC - Chapel Hill, Nanyang Technological University, School of Materials Sciences and Engineering, Singapore, Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3255, USA, Argonne National Laboratory, Department of Physics, Hampton University, Hampton, VA 23668, Korea Research Institute of Standards and Science, Daejeon, 305-600, South Korea, Department of Chemistry, Gyeongsang National University, Jinju 660-701, South Korea, Electronics and Telecommunications Research Institute, Daejeon, 305-700, South Korea, Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, MA 01609

  • Yong S. Chu

    Argonne National Laboratory