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Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy

Lakhan Bainsla, A. I. Mallick, M. Manivel Raja, A. K. Nigam, B. S. D. Ch. S. Varaprasad, Y. K. Takahashi, Aftab Alam, K. G. Suresh, and K. Hono
Phys. Rev. B 91, 104408 – Published 13 March 2015
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  • INTRODUCTION
  • EXPERIMENTAL AND COMPUTATIONAL DETAILS
  • RESULTS AND DISCUSSION
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    In this paper, we report the signature of spin gapless semiconductor (SGS) in CoFeMnSi that belongs to the Heusler family. SGS is a new class of magnetic semiconductors which have a band gap for one spin subband and zero band gap for the other, and thus are useful for tunable spin transport based applications. We show various experimental evidences for SGS behavior in CoFeMnSi by carefully carrying out the transport and spin-polarization measurements. SGS behavior is also confirmed by first-principles band-structure calculations. The most stable configuration obtained by the theoretical calculation is verified by experiment. The alloy is found to crystallize in the cubic Heusler structure (LiMgPdSn type) with some amount of disorder and has a saturation magnetization of 3.7μB/f.u. and Curie temperature of ∼620 K. The saturation magnetization is found to follow the Slater-Pauling behavior, one of the prerequisites for SGS. Nearly-temperature-independent carrier concentration and electrical conductivity are observed from 5 to 300 K. An anomalous Hall coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection data have yielded the current spin-polarization value of 0.64, which is found to be robust against the structural disorder. All these properties strongly suggest SGS nature of the alloy, which is quite promising for the spintronic applications such as spin injection as it can bridge the gap between the contrasting behaviors of half-metallic ferromagnets and semiconductors.

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    • Received 2 October 2014
    • Revised 22 February 2015

    DOI:https://doi.org/10.1103/PhysRevB.91.104408

    ©2015 American Physical Society

    Authors & Affiliations

    Lakhan Bainsla1, A. I. Mallick1, M. Manivel Raja2, A. K. Nigam3, B. S. D. Ch. S. Varaprasad4, Y. K. Takahashi4, Aftab Alam1, K. G. Suresh1,*, and K. Hono4

    • 1Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
    • 2Defence Metallurgical Research Laboratory, Hyderabad 500058, India
    • 3DCMPMS, Tata Institute of Fundamental Research, Mumbai 400005, India
    • 4Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047, Japan

    • *Corresponding author: suresh@phy.iitb.ac.in

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    Vol. 91, Iss. 10 — 1 March 2015

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    • Figure 1
      Figure 1

      Schematic of density of states for a typical (a) metal, (b) semiconductor, (c) half-metal, and (d) spin gapless semiconductor.

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    • Figure 2
      Figure 2

      Site preference energies for different configurations of CoFeMnSi. Inset: crystal structure of prototype LiMgPdSn.

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    • Figure 3
      Figure 3

      Band structure and density of states of CoFeMnSi: (a) majority-spin bands, (b) density of states, (c) minority-spin bands.

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    • Figure 4
      Figure 4

      Band gap and minimum value of DOS near the Fermi level in the majority-spin channel vs Ueff(=U−J) with different U and fixed J(=0.2eV) values. Ueff is applied only on the d electrons of Mn because of its dominant effect.

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    • Figure 5
      Figure 5

      Fe57 Mössbauer spectrum of CFMS collected at room temperature.

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    • Figure 6
      Figure 6

      (a) Temperature dependence of the electrical conductivity; σxx(T) (left-hand scale); variation of carrier concentration, n(T) with temperature (right-hand scale). (b) Representation of the field dependence of anomalous Hall effect (AHE) at 5 K. The Hall conductivity, σxy(T) is shown as the function of applied field. Inset in (b) shows the magnetization isotherm obtained at 5 K.

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    • Figure 7
      Figure 7

      Temperature dependence of Hall coefficient (RH) for CFMS alloy.

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    • Figure 8
      Figure 8

      Normalized conductance curves recorded at 4.2 K. In (a) open circles denote the measured experimental data and solid lines are the fit to the data by using modified BTK model. (b) Representation of the linear fit to P vs Z data with extrapolation down to Z=0.

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