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Accessing the fundamentals of magnetotransport in metals with terahertz probes

Abstract

Spin-dependent conduction in metals underlies all modern magnetic memory technologies, such as giant magnetoresistance (GMR). The charge current in ferromagnetic transition metals is carried by two non-mixing populations of sp-band Fermi-level electrons: one of majority-spin and one of minority-spin. These electrons experience spin-dependent momentum scattering with localized electrons, which originate from the spin-split d-band. The direct observation of magnetotransport under such fundamental conditions, however, requires magnetotransport measurements on the same timescale as the electron momentum scattering, which takes place in the sub-100 fs regime. Using terahertz electromagnetic probes, we directly observe the magnetotransport in a metallic system under the fundamental conditions, and determine the spin-dependent densities and momentum scattering times of conduction electrons. We show that traditional measurements significantly underestimate the spin asymmetry in electron scattering, a key parameter responsible for effects such as GMR. Furthermore, we demonstrate the possibility of magnetic modulation of terahertz waves, along with heat- and contact-free GMR readout using ultrafast terahertz signals.

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Figure 1: Illustration of spin-dependent conduction in a spin valve, and the sample structure.
Figure 2: Terahertz magnetospectroscopy experiment.
Figure 3: Results of terahertz magnetospectroscopy revealing the fundamental parameters of magnetotransport.

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Acknowledgements

We are grateful to A. Fert, G. Güntherodt and M. Jourdan for their comments on this work, and to Z. Mics, I. Ivanov and F. D’Angelo for helpful discussions and assistance. We acknowledge financial support by EU Career Integration Grant 334324 LIGHTER, Max Planck Society, Graduate School of Excellence Materials Science in Mainz (MAINZ) GSC 266, the EU (MASPIC, ERC-2007-StG 208162; WALL, FP7-PEOPLE-2013-ITN 608031), the DFG, Research Center of Innovative and Emerging Materials CINEMA, and the EFRE Project 81037755 ‘STeP’ (Spintronic Technology Platform Rhineland-Palatinate).

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Contributions

D.T. and M.K. conceived the project. Z.J. and D.T. performed the terahertz experiments, and A.Tkach and M.K. performed the static characterization. F.C., V.S. and H.G. produced the samples. Z.J. and D.T. analysed the terahertz data, with the help of M.B., T.K. and A.Thomas. D.T. wrote the paper with contributions from Z.J., M.K., T.K., A.Thomas and M.B. All authors discussed the results and commented on the manuscript.

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Correspondence to Dmitry Turchinovich.

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Jin, Z., Tkach, A., Casper, F. et al. Accessing the fundamentals of magnetotransport in metals with terahertz probes. Nature Phys 11, 761–766 (2015). https://doi.org/10.1038/nphys3384

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