THz emission from Co/Pt bilayers with varied roughness, crystal structure, and interface intermixing

G. Li, R. Medapalli, R. V. Mikhaylovskiy, F. E. Spada, Th. Rasing, E. E. Fullerton, and A. V. Kimel
Phys. Rev. Materials 3, 084415 – Published 19 August 2019

Abstract

Ultrafast demagnetization of Co/Pt heterostructures induced by a femtosecond 800-nm laser pulse launches a spin current from Co to Pt and subsequent conversion of the spin current to a charge current in the Pt layer due to the inverse spin-Hall effect. At the same time, due to the spin-dependent photogalvanic effect, a circularly polarized femtosecond laser pulse also generates a photocurrent at the Co/Pt interface. Both ultrashort photocurrent pulses are effectively detected in a contactless way by measuring the THz radiation they emit. Here we aim to understand how the properties of the Co/Pt interface affect the photocurrents in the bilayers. By varying the interfacial roughness, crystal structure, and interfacial intermixing, as well as having an explicit focus on the cases when THz emissions from these two photocurrents reveal opposite trends, we identify which interface properties play a crucial role for the photocurrents. In particular, we show that by reducing the roughness, the THz emission due to the spin-dependent photogalvanic effect reduces to zero while the strength of the THz emission from the photocurrent associated with the inverse spin-Hall effect increases by a factor of 2. On the other hand, while intermixing strongly enhances the THz emission from the inverse spin-Hall effect by a factor of 4.2, THz emission related to the spin-dependent photogalvanic effect reveals the opposite trend. These findings indicate that microstructural properties of the Co-Pt interface play a decisive role in the generation of photocurrents.

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  • Received 7 March 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.084415

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

G. Li1,*,†, R. Medapalli2,*, R. V. Mikhaylovskiy3, F. E. Spada2, Th. Rasing1, E. E. Fullerton2, and A. V. Kimel1,4

  • 1Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, Nijmegen, The Netherlands
  • 2Center for Memory and Recording Research, University of California, San Diego, La Jolla, California 92093-0401, USA
  • 3Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, United Kingdom
  • 4Moscow Technological University, MIREA, Vernadsky Avenue 78, Moscow 119454, Russia

  • *These authors contributed equally to this work.
  • Corresponding author: Qiao.Li@science.ru.nl

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Vol. 3, Iss. 8 — August 2019

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