Giant magnetic anisotropy and quantum tunneling of the magnetization in Li$_2$(Li$_{1-x}$Fe$_x$)N

ORAL

Abstract

The magnetic anisotropy of 3$d$ transition metals is usually considered to be weak, mainly due to the widely known paradigm of orbital quenching. However, a rare interplay of crystal electric field effects and spin-orbit coupling causes a large orbital contribution to the magnetic moment of iron in Li$_2$(Li$_{1-x}$Fe$_x$)N. This leads, not only to large magnetic moments of $\sim$\,5\,$\mu_{\rm B}$ per iron atom but, also, to an enormous magnetic anisotropy field that extrapolates to more than 200 Tesla. Magnetic hysteresis emerges for $T \leq 50$\,K and the coercivity fields of more than 11 Tesla exceed even the hardest 4$f$ electron based ferromagnets. Li$_2$(Li$_{1-x}$Fe$_x$)N not only has a clear and remarkable anisotropy, generally not associated with iron moments, but also shows time-dependence more consistent with molecular magnets. In particular for low iron concentrations $x \ll 1$ the spin-inversion is dominated by a macroscopic tunneling process rather than by thermal excitations. It is shown that the huge magnetic anisotropy makes Li$_2$(Li$_{1-x}$Fe$_x$)N (i) an ideal model system to study macroscopic quantum effects at elevated temperatures and (ii) a basis for novel magnetic functional materials.

*This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358

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Authors

  • Anton Jesche

    • The Ames Laboratory, Iowa State University, Ames, USA

  • R.W. McCallum

    • The Ames Laboratory, Iowa State University, Ames, USA
    • Ames Laboratory, U.S. DOE; Division of Materials Sciences and Engineering, Iowa State University

  • Srinivasa Thimmaiah

    • The Ames Laboratory, Iowa State University, Ames, USA

  • Jenee L Jacobs

    • The Ames Laboratory, Iowa State University, Ames, USA

  • Valentin Taufour

    • Ames Laboratory, US DOE, Iowa State University, Ames, Iowa 50011, U.S.A.
    • Critical Material Institute, Ames Laboratory, US DOE, Iowa State University, Ames, Iowa 50011, U.S.A.
    • Ames Lab, Department of Physics, Iowa State University
    • The Ames Laboratory, Iowa State University, Ames, USA

  • Andreas Kreyssig

    • Ames Laboratory and Iowa State University
    • Ames Lab., Iowa State Univ., IA
    • Ames Laboratory/ Iowa State University
    • Iowa State University
    • Ames Laboratory, Dept. Physics Astronomy, Iowa State University
    • The Ames Laboratory, Iowa State University, Ames, USA
    • Ames Laboratory and Dept. of Physics and Astronomy, Iowa State University

  • Robert S. Houk

    • The Ames Laboratory, Iowa State University, Ames, USA

  • S.L. Bud'ko

    • Ames Laboratory
    • Ames Laboratory, US DOE, Iowa State University, Ames, Iowa 50011, U.S.A.
    • Iowa State University, Ames Lab
    • Ames Laboratory/ Iowa State University
    • The Ames Laboratory, Ames, IA 50011, USA
    • The Ames Laboratory, Iowa State University, Ames, USA
    • Ames Laboratory and Dept. of Physics and Astronomy, Iowa State University

  • Paul C. Canfield

    • Ames Laboratory, US DOE, Iowa State University, Ames, Iowa 50011, U.S.A.
    • Iowa State University, Ames Lab
    • Ames Laboratory/ Iowa State University
    • Iowa State University
    • Ames Laboratory
    • Iowa State Univ
    • Ames Laboratory and Dept. of Physics, Iowa State University
    • The Ames Laboratory, Ames, IA 50011, USA
    • Ames Lab, Department of Physics, Iowa State University
    • The Ames Laboratory, Iowa State University, Ames, USA
    • Ames Laboratory and Dept. of Physics and Astronomy, Iowa State University