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Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band

Nature Materials volume 11, pages 444–449 (2012)Cite this article

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Abstract

The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature TC. It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band. Here we combine results of channelling experiments, which measure the concentrations both of Mn ions and of holes relevant to the ferromagnetic order, with magnetization, transport, and magneto-optical data to address this issue. Taken together, these measurements provide strong evidence that it is the location of the Fermi level within the impurity band that determines TC through determining the degree of hole localization. This finding differs drastically from the often accepted view that TC is controlled by valence band holes, thus opening new avenues for achieving higher values of TC.

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Figure 1: Comparison between experimental data and theoretical calculations based on the valence band model of Jungwirth et al.33.
Figure 2: Effect of annealing on transport properties of (Ga,Mn)As samples.
Figure 3: Schematic representation of the origin of MCD in (Ga,Mn)As.
Figure 4: MCD spectra.
Figure 5: Comparison between MCD spectra for samples F and F*.

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Acknowledgements

K.T. thanks Y-Y. Zhou for her help with the MCD set-up and sample preparation. This work was supported by the National Science Foundation Grant DMR 10-05851; by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institute for Advanced Research (CIFAR) and by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under Contract No. DE — AC02-05CH11231.

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Authors and Affiliations

  1. Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA

    M. Dobrowolska, K. Tivakornsasithorn, X. Liu & J. K. Furdyna

  2. Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada

    M. Berciu

  3. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA

    K. M. Yu & W. Walukiewicz

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  1. M. Dobrowolska
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Contributions

M.D. and M.B. conceived the project and wrote the manuscript. K.T. carried out the MCD, transport and magnetization experiments with guidance from X.L., M.D. and J.K.F. X.L. fabricated the samples and contributed to the manuscript. K.M.Y. and W.W. are responsible for the channelling experiments. The project was supervised by M.D. and J.K.F. All authors have reviewed, discussed and approved the results and conclusions of this article.

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Correspondence to M. Dobrowolska.

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Dobrowolska, M., Tivakornsasithorn, K., Liu, X. et al. Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band. Nature Mater 11, 444–449 (2012). https://doi.org/10.1038/nmat3250

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