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Spin polarization in half-metals probed by femtosecond spin excitation

Nature Materials volume 8, pages 56–61 (2009)Cite this article

Abstract

Knowledge of the spin polarization is of fundamental importance for the use of a material in spintronics applications. Here, we used femtosecond optical excitation of half-metals to distinguish between half-metallic and metallic properties. Because the direct energy transfer by Elliot–Yafet scattering is blocked in a half-metal, the demagnetization time is a measure for the degree of half-metallicity. We propose that this characteristic enables us vice versa to establish a novel and fast characterization tool for this highly important material class used in spin-electronic devices. The technique has been applied to a variety of materials where the spin polarization at the Fermi level ranges from 45 to 98%: Ni, Co2MnSi, Fe3O4, La0.66Sr0.33MnO3 and CrO2.

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Figure 1: Schematic representation of the ‘classical’ techniques to determine the spin polarization P of a material.
Figure 2: Three-temperature model as determined by rate equations.
Figure 3: Study of the spin polarization using all-optical pump–probe experiments to determine the demagnetization time τm.
Figure 4: Classification of the materials by the value of the spin polarization P and their demagnetization time τm.
Figure 5: All-optical pump–probe experiments shown on the short timescale to reveal the demagnetization by spin flips of the non-thermalized electrons.

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Acknowledgements

Support by the Deutsche Forschungsgemeinschaft within the priority program SPP 1133 and SFB 602 is gratefully acknowledged. In MIT, the work is supported by NSF and ONR grants; at the University of Alabama, support by a NSF MRSEC grant is gratefully acknowledged. M.M. thanks J. Stöhr and B. Koopmans for fruitful discussions.

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Authors and Affiliations

  1. IV. Phys. Institut, Universität Göttingen, D-37077 Göttingen, Germany

    Georg M. Müller, Jakob Walowski, Marija Djordjevic & Markus Münzenberg

  2. MINT Center, University of Alabama, Tuscaloosa, Alabama 35487, USA

    Gou-Xing Miao & Arunava Gupta

  3. CEA Saclay, 91191 Gif sur Yvette Cedex, France

    Ana V. Ramos

  4. I. Phys. Institut, Universität Göttingen, D-37077 Göttingen, Germany

    Kai Gehrke, Vasily Moshnyaga & Konrad Samwer

  5. Department of Physics, Universität Bielefeld, D-33501 Bielefeld, Germany

    Jan Schmalhorst, Andy Thomas, Andreas Hütten & Günter Reiss

  6. Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    Jagadeesh S. Moodera

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  1. Georg M. Müller
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Contributions

M.M. designed research and model; G.M.M., J.W., M.D. and M.M. carried out research (femtosecond dynamics), G.M.M. main contributor to experiment execution and data analysis; G.X.M., A.G., A.V.R., K.G., V.M., K.S., J.S., A.T., A.H. and G.R. carried out research (spin transport, film growth and characterization); M.M. wrote the manuscript; J.S.M. and M.M. coordinated research.

Corresponding author

Correspondence to Markus Münzenberg.

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Müller, G., Walowski, J., Djordjevic, M. et al. Spin polarization in half-metals probed by femtosecond spin excitation. Nature Mater 8, 56–61 (2009). https://doi.org/10.1038/nmat2341

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