Thin-film stacks F|H consisting of a ferromagnetic-metal layer F and a heavy-metal layer H are spintronic model systems. Here, we present a method to measure the ultrabroadband spin conductance across a layer X between F and H at terahertz frequencies, which are the natural frequencies of spin-transport dynamics. We apply our approach to MgO tunneling barriers with thickness d = 0-6 Å. In the time domain, the spin conductance Gs has two components. An instantaneous feature arises from processes like coherent spin tunneling. Remarkably, a longer-lived component is a hallmark of incoherent resonant spin tunneling mediated by MgO defect states, because its relaxation time grows monotonically with d to as much as 270 fs at d = 6.0 Å. Our results are in full agreement with an analytical model. They indicate that terahertz spin-conductance spectroscopy will yield new and relevant insights into ultrafast spin transport in a wide range of spintronic nanostructures.

Department of Physical Chemistry Fritz Haber Institute of the Max Planck Society 14195 Berlin Germany

Department of Physics Freie Universität Berlin 14195 Berlin Germany

Faculty of Mathematics and Physics Charles University Ke Karlovu 3 121 16 Prague Czech Republic

Institut für Physik Martin Luther Universität Halle 06120 Halle Germany

Max Planck Institute for Microstructure Physics Weinberg 2 06120 Halle Germany

Zobrazit více v PubMed

del Alamo J. A. Nanometre-scale electronics with III–V compound semiconductors. Nature 2011, 479 (7373), 317–323. 10.1038/nature10677. PubMed DOI

Hillerkuss D.; Schmogrow R.; Schellinger T.; Jordan M.; Winter M.; Huber G.; Vallaitis T.; Bonk R.; Kleinow P.; Frey F.; Roeger M.; Koenig S.; Ludwig A.; Marculescu A.; Li J.; Hoh M.; Dreschmann M.; Meyer J.; Ben Ezra S.; Narkiss N.; Nebendahl B.; Parmigiani F.; Petropoulos P.; Resan B.; Oehler A.; Weingarten K.; Ellermeyer T.; Lutz J.; Moeller M.; Huebner M.; Becker J.; Koos C.; Freude W.; Leuthold J. 26 Tbit s–1 line-rate super-channel transmission utilizing all-optical fast Fourier transform processing. Nat. Photonics 2011, 5 (6), 364–371. 10.1038/nphoton.2011.74. DOI

Kirilyuk A.; Kimel A. V.; Rasing T. Ultrafast optical manipulation of magnetic order. Rev. Mod. Phys. 2010, 82 (3), 2731–2784. 10.1103/RevModPhys.82.2731. DOI

Kampfrath T.; Battiato M.; Maldonado P.; Eilers G.; Nötzold J.; Mährlein S.; Zbarsky V.; Freimuth F.; Mokrousov Y.; Blügel S.; Wolf M.; Radu I.; Oppeneer P. M.; Münzenberg M. Terahertz spin current pulses controlled by magnetic heterostructures. Nat. Nanotechnol. 2013, 8 (4), 256–260. 10.1038/nnano.2013.43. PubMed DOI

Zhou C.; Liu Y. P.; Wang Z.; Ma S. J.; Jia M. W.; Wu R. Q.; Zhou L.; Zhang W.; Liu M. K.; Wu Y. Z.; Qi J. Broadband Terahertz Generation via the Interface Inverse Rashba-Edelstein Effect. Phys. Rev. Lett. 2018, 121 (8), 08680110.1103/PhysRevLett.121.086801. PubMed DOI

Seifert T.; Jaiswal S.; Martens U.; Hannegan J.; Braun L.; Maldonado P.; Freimuth F.; Kronenberg A.; Henrizi J.; Radu I.; Beaurepaire E.; Mokrousov Y.; Oppeneer P. M.; Jourdan M.; Jakob G.; Turchinovich D.; Hayden L. M.; Wolf M.; Münzenberg M.; Kläui M.; Kampfrath T. Efficient metallic spintronic emitters of ultrabroadband terahertz radiation. Nat. Photonics 2016, 10 (7), 483–488. 10.1038/nphoton.2016.91. DOI

Rouzegar R.; Brandt L.; Nádvorník L.; Reiss D. A.; Chekhov A. L.; Gueckstock O.; In C.; Wolf M.; Seifert T. S.; Brouwer P. W.; Woltersdorf G.; Kampfrath T. Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization. Phys. Rev. B 2022, 106 (14), 14442710.1103/PhysRevB.106.144427. DOI

Seifert T. S.; Jaiswal S.; Barker J.; Weber S. T.; Razdolski I.; Cramer J.; Gueckstock O.; Maehrlein S. F.; Nadvornik L.; Watanabe S.; Ciccarelli C.; Melnikov A.; Jakob G.; Münzenberg M.; Goennenwein S. T. B.; Woltersdorf G.; Rethfeld B.; Brouwer P. W.; Wolf M.; Kläui M.; Kampfrath T. Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy. Nat. Commun. 2018, 9 (1), 2899.10.1038/s41467-018-05135-2. PubMed DOI PMC

Seifert T. S.; Tran N. M.; Gueckstock O.; Rouzegar S. M.; Nadvornik L.; Jaiswal S.; Jakob G.; Temnov V. V.; Münzenberg M.; Wolf M.; Kläui M.; Kampfrath T. Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu80Ir20. J. Phys. D: Appl. Phys. 2018, 51 (36), 36400310.1088/1361-6463/aad536. DOI

Gorchon J.; Mangin S.; Hehn M.; Malinowski G. Is terahertz emission a good probe of the spin current attenuation length?. Appl. Phys. Lett. 2022, 121 (1), 012402.10.1063/5.0097448. DOI

Wahada M. A.; Şaşıoğlu E.; Hoppe W.; Zhou X.; Deniz H.; Rouzegar R.; Kampfrath T.; Mertig I.; Parkin S. S. P.; Woltersdorf G. Atomic Scale Control of Spin Current Transmission at Interfaces. Nano Lett. 2022, 22 (9), 3539–3544. 10.1021/acs.nanolett.1c04358. PubMed DOI PMC

Schneider R.; Fix M.; Bensmann J.; Michaelis de Vasconcellos S.; Albrecht M.; Bratschitsch R. Spintronic GdFe/Pt THz emitters. Appl. Phys. Lett. 2019, 115 (15), 15240110.1063/1.5120249. DOI

Kholid F. N.; Hamara D.; Hamdan A. F. B.; Nava Antonio G.; Bowen R.; Petit D.; Cowburn R.; Pisarev R. V.; Bossini D.; Barker J.; Ciccarelli C. The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures. Nat. Commun. 2023, 14 (1), 538.10.1038/s41467-023-36166-z. PubMed DOI PMC

Dang T. H.; Hawecker J.; Rongione E.; Baez Flores G.; To D. Q.; Rojas-Sanchez J. C.; Nong H.; Mangeney J.; Tignon J.; Godel F.; Collin S.; Seneor P.; Bibes M.; Fert A.; Anane M.; George J.-M.; Vila L.; Cosset-Cheneau M.; Dolfi D.; Lebrun R.; Bortolotti P.; Belashchenko K.; Dhillon S.; Jaffrès H. Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy. Applied Physics Reviews 2020, 7 (4), 041409.10.1063/5.0022369. DOI

Bauer G. E. W.; Saitoh E.; van Wees B. J. Spin caloritronics. Nat. Mater. 2012, 11 (5), 391–399. 10.1038/nmat3301. PubMed DOI

Manchon A.; Železný J.; Miron I. M.; Jungwirth T.; Sinova J.; Thiaville A.; Garello K.; Gambardella P. Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems. Rev. Mod. Phys. 2019, 91 (3), 03500410.1103/RevModPhys.91.035004. DOI

Sinova J.; Valenzuela S. O.; Wunderlich J.; Back C. H.; Jungwirth T. Spin Hall effects. Rev. Mod. Phys. 2015, 87 (4), 1213–1260. 10.1103/RevModPhys.87.1213. DOI

Seifert T. S.; Cheng L.; Wei Z.; Kampfrath T.; Qi J. Spintronic sources of ultrashort terahertz electromagnetic pulses. Appl. Phys. Lett. 2022, 120 (18), 18040110.1063/5.0080357. DOI

Bierhance G.; Markou A.; Gueckstock O.; Rouzegar R.; Behovits Y.; Chekhov A. L.; Wolf M.; Seifert T. S.; Felser C.; Kampfrath T. Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co2MnGa and Co2MnAl. Appl. Phys. Lett. 2022, 120 (8), 08240110.1063/5.0080308. DOI

Yuasa S.; Djayaprawira D. D. Giant tunnel magnetoresistance in magnetic tunnel junctions with a crystalline MgO(0 0 1) barrier. J. Phys. D: Appl. Phys. 2007, 40 (21), R337.10.1088/0022-3727/40/21/R01. DOI

Apalkov D.; Dieny B.; Slaughter J. M. Magnetoresistive random access memory. Proceedings of the IEEE 2016, 104 (10), 1796–1830. 10.1109/JPROC.2016.2590142. DOI

Wang L.; Cheng H.; Li P.; Van Hees Y. L. W.; Liu Y.; Cao K.; Lavrijsen R.; Lin X.; Koopmans B.; Zhao W. Picosecond optospintronic tunnel junctions. Proc. Natl. Acad. Sci. U. S. A. 2022, 119 (24), e2204732119.10.1073/pnas.2204732119. DOI

Jin Z.; Li J.; Zhang W.; Guo C.; Wan C.; Han X.; Cheng Z.; Zhang C.; Balakin A. V.; Shkurinov A. P.; Peng Y.; Ma G.; Zhu Y.; Yao J.; Zhuang S. Magnetic Modulation of Terahertz Waves via Spin-Polarized Electron Tunneling Based on Magnetic Tunnel Junctions. Physical Review Applied 2020, 14 (1), 01403210.1103/PhysRevApplied.14.014032. DOI

Jechumtál J.; Rouzegar R.; Gueckstock O.; Denker C.; Hoppe W.; Remy Q.; Seifert T. S.; Kubaščík P.; Woltersdorf G.; Brouwer P. W.; Münzenberg M.; Kampfrath T.; Nádvorník L. Accessing Ultrafast Spin-Transport Dynamics in Copper Using Broadband Terahertz Spectroscopy. Phys. Rev. Lett. 2024, 132 (22), 22670310.1103/PhysRevLett.132.226703. PubMed DOI

Rouzegar R.; Chekhov A. L.; Behovits Y.; Serrano B. R.; Syskaki M. A.; Lambert C. H.; Engel D.; Martens U.; Münzenberg M.; Wolf M.; Jakob G.; Kläui M.; Seifert T. S.; Kampfrath T. Broadband Spintronic Terahertz Source with Peak Electric Fields Exceeding 1.5 MV/cm. Physical Review Applied 2023, 19 (3), 03401810.1103/PhysRevApplied.19.034018. DOI

Chekhov A. L.; Behovits Y.; Heitz J. J. F.; Denker C.; Reiss D. A.; Wolf M.; Weinelt M.; Brouwer P. W.; Münzenberg M.; Kampfrath T. Ultrafast Demagnetization of Iron Induced by Optical versus Terahertz Pulses. Physical Review X 2021, 11 (4), 04105510.1103/PhysRevX.11.041055. DOI

Naylor D. A.; Tahic M. K. Apodizing functions for Fourier transform spectroscopy. J. Opt. Soc. Am. A 2007, 24 (11), 3644–3648. 10.1364/JOSAA.24.003644. PubMed DOI

Mather P. G.; Read J. C.; Buhrman R. A. Disorder, defects, and band gaps in ultrathin (001) MgO tunnel barrier layers. Phys. Rev. B 2006, 73 (20), 20541210.1103/PhysRevB.73.205412. DOI

Cha J. J.; Read J. C.; Buhrman R. A.; Muller D. A. Spatially resolved electron energy-loss spectroscopy of electron-beam grown and sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions. Appl. Phys. Lett. 2007, 91 (6), 06251610.1063/1.2769753. DOI

Velev J. P.; Belashchenko K. D.; Jaswal S. S.; Tsymbal E. Y. Effect of oxygen vacancies on spin-dependent tunneling in Fe/MgO/Fe magnetic tunnel junctions. Appl. Phys. Lett. 2007, 90 (7), 07250210.1063/1.2643027. DOI

Miao G. X.; Park Y. J.; Moodera J. S.; Seibt M.; Eilers G.; Münzenberg M. Disturbance of Tunneling Coherence by Oxygen Vacancy in Epitaxial $\mathrm{Fe}/\mathrm{MgO}/\mathrm{Fe}$ Magnetic Tunnel Junctions. Phys. Rev. Lett. 2008, 100 (24), 24680310.1103/PhysRevLett.100.246803. PubMed DOI

Ke Y.; Xia K.; Guo H. Oxygen-Vacancy-Induced Diffusive Scattering in $\mathrm{Fe}/\mathrm{MgO}/\mathrm{Fe}$ Magnetic Tunnel Junctions. Phys. Rev. Lett. 2010, 105 (23), 23680110.1103/PhysRevLett.105.236801. PubMed DOI

Tsymbal E. Y.; Pettifor D. G. Local impurity-assisted conductance in magnetic tunnel junctions. Phys. Rev. B 2001, 64 (21), 21240110.1103/PhysRevB.64.212401. DOI

König T.; Simon G. H.; Rust H. P.; Heyde M. Work Function Measurements of Thin Oxide Films on Metals—MgO on Ag(001). J. Phys. Chem. C 2009, 113 (26), 11301–11305. 10.1021/jp901226q. DOI

Teixeira J. M.; Ventura J.; Carpinteiro F.; Araujo J. P.; Sousa J. B.; Wisniowski P.; Freitas P. P. The effect of pinhole formation/growth on the tunnel magnetoresistance of MgO-based magnetic tunnel junctions. J. Appl. Phys. 2009, 106 (7), 07370710.1063/1.3236512. DOI

König T.; Simon G. H.; Rust H. P.; Pacchioni G.; Heyde M.; Freund H. J. Measuring the Charge State of Point Defects on MgO/Ag(001). J. Am. Chem. Soc. 2009, 131 (48), 17544–17545. 10.1021/ja908049n. PubMed DOI

Mathon J.; Umerski A. Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe(001) junction. Phys. Rev. B 2001, 63 (22), 22040310.1103/PhysRevB.63.220403. DOI

Butler W. H.; Zhang X. G.; Schulthess T. C.; MacLaren J. M. Spin-dependent tunneling conductance of $\mathrm{Fe}|\mathrm{MgO}|\mathrm{Fe}$ sandwiches. Phys. Rev. B 2001, 63 (5), 05441610.1103/PhysRevB.63.054416. DOI

Butler W. H. Tunneling magnetoresistance from a symmetry filtering effect. Sci. Technol. Adv. Mater. 2008, 9 (1), 01410610.1088/1468-6996/9/1/014106. PubMed DOI PMC

Velev J. P.; Zhuravlev M. Y.; Belashchenko K. D.; Jaswal S. S.; Tsymbal E. Y.; Katayama T.; Yuasa S. Defect-Mediated Properties of Magnetic Tunnel Junctions. IEEE Trans. Magn. 2007, 43 (6), 2770–2775. 10.1109/TMAG.2007.893311. DOI

Gadzuk J. W. Resonance Tunneling Through Impurity States in Metal-Insulator-Metal Junctions. J. Appl. Phys. 1970, 41 (1), 286–291. 10.1063/1.1658335. DOI

Teixeira J. M.; Ventura J.; Araujo J. P.; Sousa J. B.; Wisniowski P.; Cardoso S.; Freitas P. P. Resonant Tunneling through Electronic Trapping States in Thin MgO Magnetic Junctions. Phys. Rev. Lett. 2011, 106 (19), 196601.10.1103/PhysRevLett.106.196601. PubMed DOI

Landsman A. S.; Weger M.; Maurer J.; Boge R.; Ludwig A.; Heuser S.; Cirelli C.; Gallmann L.; Keller U. Ultrafast resolution of tunneling delay time. Optica 2014, 1 (5), 343–349. 10.1364/OPTICA.1.000343. DOI

Mathon J.; Umerski A. Theory of resonant tunneling in an epitaxialFe/Au/MgO/Au/Fe(001)junction. Phys. Rev. B 2005, 71 (22), 220402.10.1103/PhysRevB.71.220402. DOI

Yuasa S.; Nagahama T.; Suzuki Y. Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions. Science 2002, 297 (5579), 234–237. 10.1126/science.1071300. PubMed DOI

Lu Z.-Y.; Zhang X. G.; Pantelides S. T. Spin-Dependent Resonant Tunneling through Quantum-Well States in Magnetic Metallic Thin Films. Phys. Rev. Lett. 2005, 94 (20), 207210.10.1103/PhysRevLett.94.207210. PubMed DOI

Glazov M. M.; Alekseev P. S.; Odnoblyudov M. A.; Chistyakov V. M.; Tarasenko S. A.; Yassievich I. N. Spin-dependent resonant tunneling in symmetrical double-barrier structures. Phys. Rev. B 2005, 71 (15), 15531310.1103/PhysRevB.71.155313. DOI

Xu Y.; Ephron D.; Beasley M. R. Directed inelastic hopping of electrons through metal-insulator-metal tunnel junctions. Phys. Rev. B 1995, 52 (4), 2843–2859. 10.1103/PhysRevB.52.2843. PubMed DOI

Yuasa S.; Nagahama T.; Fukushima A.; Suzuki Y.; Ando K. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nat. Mater. 2004, 3 (12), 868–871. 10.1038/nmat1257. PubMed DOI

Mukherjee S. S.; Bai F.; MacMahon D.; Lee C.-L.; Gupta S. K.; Kurinec S. K. Crystallization and grain growth behavior of CoFeB and MgO layers in multilayer magnetic tunnel junctions. J. Appl. Phys. 2009, 106 (3), 03390610.1063/1.3176501. DOI

Choi Y. S.; Tsunekawa K.; Nagamine Y.; Djayaprawira D. Transmission electron microscopy study on the polycrystalline CoFeB/MgO/CoFeB based magnetic tunnel junction showing a high tunneling magnetoresistance, predicted in single crystal magnetic tunnel junction. J. Appl. Phys. 2007, 101 (1), 013907.10.1063/1.2407270. DOI

Papaioannou E. T.; Beigang R. THz spintronic emitters: a review on achievements and future challenges. Nanophotonics 2021, 10 (4), 1243–1257. 10.1515/nanoph-2020-0563. DOI

Feng Z.; Qiu H.; Wang D.; Zhang C.; Sun S.; Jin B.; Tan W. Spintronic terahertz emitter. J. Appl. Phys. 2021, 129 (1), 010901.10.1063/5.0037937. DOI

Cheng L.; Li Z.; Zhao D.; Chia E. E. M. Studying spin–charge conversion using terahertz pulses. APL Materials 2021, 9 (7), 070902.10.1063/5.0051217. DOI

Bull C.; Hewett S. M.; Ji R.; Lin C.-H.; Thomson T.; Graham D. M.; Nutter P. W. Spintronic terahertz emitters: Status and prospects from a materials perspective. APL Materials 2021, 9 (9), 090701.10.1063/5.0057511. DOI

Wu W.; Yaw Ameyaw C.; Doty M. F.; Jungfleisch M. B. Principles of spintronic THz emitters. J. Appl. Phys. 2021, 130 (9), 09110110.1063/5.0057536. DOI

Krewer K. L.; Zhang W.; Arabski J.; Schmerber G.; Beaurepaire E.; Bonn M.; Turchinovich D. Thickness-dependent electron momentum relaxation times in iron films. Appl. Phys. Lett. 2020, 116 (10), 102406.10.1063/1.5142479. DOI

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. Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions. Physical Review X 2021, 11 (2), 02103010.1103/PhysRevX.11.021030. DOI

Melnikov A.; Brandt L.; Liebing N.; Ribow M.; Mertig I.; Woltersdorf G. Ultrafast spin transport and control of spin current pulse shape in metallic multilayers. Phys. Rev. B 2022, 106 (10), 104417.10.1103/PhysRevB.106.104417. DOI

Lee K.; Lee D.-K.; Yang D.; Mishra R.; Kim D.-J.; Liu S.; Xiong Q.; Kim S. K.; Lee K.-J.; Yang H. Superluminal-like magnon propagation in antiferromagnetic NiO at nanoscale distances. Nat. Nanotechnol. 2021, 16 (12), 1337–1341. 10.1038/s41565-021-00983-4. PubMed DOI

Sasaki Y.; Li G.; Moriyama T.; Ono T.; Mikhaylovskiy R. V.; Kimel A. V.; Mizukami S. Laser stimulated THz emission from Pt/CoO/FeCoB. Appl. Phys. Lett. 2020, 117 (19), 192403.10.1063/5.0020020. DOI

Gueckstock O.; Seeger R. L.; Seifert T. S.; Auffret S.; Gambarelli S.; Kirchhof J. N.; Bolotin K. I.; Baltz V.; Kampfrath T.; Nádvorník L. Impact of gigahertz and terahertz transport regimes on spin propagation and conversion in the antiferromagnet IrMn. Appl. Phys. Lett. 2022, 120 (6), 062408.10.1063/5.0077868. DOI