Optimum excitation wavelength and photon energy threshold for spintronic terahertz emission from Fe/Pt bilayer
Valynn Katrine Mag-usara,
Mary Clare Escaño,
Christopher E. Petoukhoff,
Garik Torosyan,
Laura Scheuer,
Julien Madéo,
Jessica Afalla,
Miezel L. Talara,
Joselito E. Muldera,
Hideaki Kitahara,
David R. Bacon,
Makoto Nakajima,
Keshav Dani,
Evangelos Th. Papaioannou,
René Beigang,
Masahiko Tani
Affiliations
Valynn Katrine Mag-usara
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan; Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan; Corresponding author
Mary Clare Escaño
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan
Christopher E. Petoukhoff
Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan; KAUST Solar Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
Garik Torosyan
Photonic Center Kaiserslautern, Kaiserslautern 67663, Germany
Laura Scheuer
Department of Physics, Technical University of Kaiserslautern, Kaiserslautern 67663, Germany
Julien Madéo
Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan
Jessica Afalla
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan; Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan
Miezel L. Talara
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan
Joselito E. Muldera
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan
Hideaki Kitahara
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan
David R. Bacon
Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan
Makoto Nakajima
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Keshav Dani
Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan
Evangelos Th. Papaioannou
Institute of Physics, Martin Luther University of Halle-Wittenberg, Halle 06108, Germany
René Beigang
Department of Physics, Technical University of Kaiserslautern, Kaiserslautern 67663, Germany
Masahiko Tani
Research Center for Development of Far-infrared Region, University of Fukui, Fukui 910-8507, Japan
Summary: Terahertz emission from ferromagnetic/non-magnetic spintronic heterostructures had been demonstrated as pump wavelength-independent. We report, however, the pump wavelength dependence of terahertz emission from an optimized Fe/Pt spintronic bilayer on MgO substrate. Maximum terahertz generation per total pump power was observed in the 1200- to 1800-nm pump wavelength range, and a marked decrease in the terahertz emission efficiency beyond 2500 nm (pump photon energies <0.5 eV) suggests a ∼0.35-eV threshold pump photon energy for effective spintronic terahertz emission. The inferred threshold is supported by previous theoretical results on the onset energy of significant spin-filtering at the Fe-Pt interface, and confirmed by Fe/Pt electronic structure calculations in this present work. The results of terahertz time-domain emission spectroscopy show the sensitivity of spintronic terahertz emission to both the optical absorptance of the heterostructure and the energy-dependent spin transport, as dictated by the properties of the metallic thin films.
