Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions

Lukáš Nádvorník; Martin Borchert; Liane Brandt; Richard Schlitz; Koen A. de Mare; Karel Výborný; Ingrid Mertig; Gerhard Jakob; Matthias Kläui; Sebastian T.B. Goennenwein; Martin Wolf; Georg Woltersdorf; Tobias Kampfrath

doi:10.1103/PhysRevX.11.021030

Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions

Lukáš Nádvorník (Corresponding author), Martin Borchert, Liane Brandt, Richard Schlitz, Koen A. de Mare, Karel Výborný, Ingrid Mertig, Gerhard Jakob, Matthias Kläui, Sebastian T.B. Goennenwein, Martin Wolf, Georg Woltersdorf, Tobias Kampfrath

Applied Physics and Science Education

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Abstract

Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e., spin-dependent electron scattering), whereas intrinsic (i.e., scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19, and Ni50Fe50 over the frequency range from dc to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory reveals that the AMR of the Ni, Ni81Fe19, and Ni50Fe50 samples is of predominantly extrinsic nature. However, the Co thin film exhibits a sizable intrinsic AMR contribution, which is constant up to 28 THz and amounts to more than 2/3 of the dc AMR contrast of 1%. These features are attributed to the hexagonal structure of the Co crystallites. They are interesting for applications in terahertz spintronics and terahertz photonics. Our results show that broadband terahertz electromagnetic pulses provide new and contact-free insights into magnetotransport phenomena of standard magnetic thin films on ultrafast timescales.

Original language	English
Article number	021030
Number of pages	16
Journal	Physical Review X
Volume	11
Issue number	2
DOIs	https://doi.org/10.1103/PhysRevX.11.021030
Publication status	Published - 7 May 2021

Bibliographical note

Funding Information:
We acknowledge funding by the German Research Foundation through collaborative research centers SFB TRR 227 “Ultrafast spin dynamics” (projects A05, B02, and B04) and SFB TRR 173 “Spin+X”/Project No. 268565370/TRR173 (projects A01 and B02). We thank the ERC for support through the Horizon2020 projects CoG TERAMAG/Grant No. 681917, SyG 3D MAGiC/Grant No. 856538, and ASPIN/Grant No. 766566. We acknowledge financial support from the Horizon 2020 Framework Programme of the European Commission under FET-Open Grant No. 863155 (s-Nebula) and from the Grant Agency of the Czech Republic under EXPRO Grant No. 19-28375X.

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Nádvorník, L., Borchert, M., Brandt, L., Schlitz, R., de Mare, K. A., Výborný, K., Mertig, I., Jakob, G., Kläui, M., Goennenwein, S. T. B., Wolf, M., Woltersdorf, G., & Kampfrath, T. (2021). Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions. Physical Review X, 11(2), Article 021030. https://doi.org/10.1103/PhysRevX.11.021030

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title = "Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions",

abstract = "Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e., spin-dependent electron scattering), whereas intrinsic (i.e., scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19, and Ni50Fe50 over the frequency range from dc to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory reveals that the AMR of the Ni, Ni81Fe19, and Ni50Fe50 samples is of predominantly extrinsic nature. However, the Co thin film exhibits a sizable intrinsic AMR contribution, which is constant up to 28 THz and amounts to more than 2/3 of the dc AMR contrast of 1%. These features are attributed to the hexagonal structure of the Co crystallites. They are interesting for applications in terahertz spintronics and terahertz photonics. Our results show that broadband terahertz electromagnetic pulses provide new and contact-free insights into magnetotransport phenomena of standard magnetic thin films on ultrafast timescales.",

author = "Luk{\'a}{\v s} N{\'a}dvorn{\'i}k and Martin Borchert and Liane Brandt and Richard Schlitz and {de Mare}, {Koen A.} and Karel V{\'y}born{\'y} and Ingrid Mertig and Gerhard Jakob and Matthias Kl{\"a}ui and Goennenwein, {Sebastian T.B.} and Martin Wolf and Georg Woltersdorf and Tobias Kampfrath",

note = "Funding Information: We acknowledge funding by the German Research Foundation through collaborative research centers SFB TRR 227 “Ultrafast spin dynamics” (projects A05, B02, and B04) and SFB TRR 173 “Spin+X”/Project No. 268565370/TRR173 (projects A01 and B02). We thank the ERC for support through the Horizon2020 projects CoG TERAMAG/Grant No. 681917, SyG 3D MAGiC/Grant No. 856538, and ASPIN/Grant No. 766566. We acknowledge financial support from the Horizon 2020 Framework Programme of the European Commission under FET-Open Grant No. 863155 (s-Nebula) and from the Grant Agency of the Czech Republic under EXPRO Grant No. 19-28375X. ",

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Nádvorník, L, Borchert, M, Brandt, L, Schlitz, R, de Mare, KA, Výborný, K, Mertig, I, Jakob, G, Kläui, M, Goennenwein, STB, Wolf, M, Woltersdorf, G & Kampfrath, T 2021, 'Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions', Physical Review X, vol. 11, no. 2, 021030. https://doi.org/10.1103/PhysRevX.11.021030

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AU - Nádvorník, Lukáš

AU - Borchert, Martin

AU - Brandt, Liane

AU - Schlitz, Richard

AU - de Mare, Koen A.

AU - Výborný, Karel

AU - Mertig, Ingrid

AU - Jakob, Gerhard

AU - Kläui, Matthias

AU - Goennenwein, Sebastian T.B.

AU - Wolf, Martin

AU - Woltersdorf, Georg

AU - Kampfrath, Tobias

N1 - Funding Information: We acknowledge funding by the German Research Foundation through collaborative research centers SFB TRR 227 “Ultrafast spin dynamics” (projects A05, B02, and B04) and SFB TRR 173 “Spin+X”/Project No. 268565370/TRR173 (projects A01 and B02). We thank the ERC for support through the Horizon2020 projects CoG TERAMAG/Grant No. 681917, SyG 3D MAGiC/Grant No. 856538, and ASPIN/Grant No. 766566. We acknowledge financial support from the Horizon 2020 Framework Programme of the European Commission under FET-Open Grant No. 863155 (s-Nebula) and from the Grant Agency of the Czech Republic under EXPRO Grant No. 19-28375X.

PY - 2021/5/7

Y1 - 2021/5/7

N2 - Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e., spin-dependent electron scattering), whereas intrinsic (i.e., scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19, and Ni50Fe50 over the frequency range from dc to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory reveals that the AMR of the Ni, Ni81Fe19, and Ni50Fe50 samples is of predominantly extrinsic nature. However, the Co thin film exhibits a sizable intrinsic AMR contribution, which is constant up to 28 THz and amounts to more than 2/3 of the dc AMR contrast of 1%. These features are attributed to the hexagonal structure of the Co crystallites. They are interesting for applications in terahertz spintronics and terahertz photonics. Our results show that broadband terahertz electromagnetic pulses provide new and contact-free insights into magnetotransport phenomena of standard magnetic thin films on ultrafast timescales.

AB - Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e., spin-dependent electron scattering), whereas intrinsic (i.e., scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19, and Ni50Fe50 over the frequency range from dc to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory reveals that the AMR of the Ni, Ni81Fe19, and Ni50Fe50 samples is of predominantly extrinsic nature. However, the Co thin film exhibits a sizable intrinsic AMR contribution, which is constant up to 28 THz and amounts to more than 2/3 of the dc AMR contrast of 1%. These features are attributed to the hexagonal structure of the Co crystallites. They are interesting for applications in terahertz spintronics and terahertz photonics. Our results show that broadband terahertz electromagnetic pulses provide new and contact-free insights into magnetotransport phenomena of standard magnetic thin films on ultrafast timescales.

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DO - 10.1103/PhysRevX.11.021030

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Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions

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