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.

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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