Terahertz Emission Properties from Fe/Pt Metallic Spintronic Hetero-Structures

Abstract

Spintronic terahertz (THz) emitters [1]–[2], consisting of ultrathin ferromagnetic and non-ferromagnetic metallic layers, have advantages over conventional THz emitters, such as photoconductive antennas (PCAs). For example, the emission bandwidth is much broader than a typical PCA [2]. A broad range of optical pump wavelength from UV to near IR region, including the communication wavelength <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\sim 1.5 \mu \mathrm{m})$</tex> is usable [3]–[4]. However, the efficiency of spintronic emitters is still low compared to PCAs. Therefore, improvement of the THz emission efficiency of spintronic emitters is the most important technical issue for development of practical THz spintronic emitters. Fe/Pt heterostructure [5] is one of the most efficient spintronic THz emitters among those reported so far. In this work, the authors report their investigations on this type of THz spintronic emitter. Firstly, the optimization of the layer structure and thickness [5] is discussed. The saturation and damage threshold properties with the optical pump power, which are important for the pump power scalability, are reported. We have investigated the pump wavelength dependence of THz emission from the spintronic device from 400 nm to 2700 nm, and found that the THz emission efficiency (THz emission/pump power) gradually decrease from 1500 nm to the threshold wavelength around 2800 nm. In addition, a diabolo-shaped Fe/Pt antenna is fabricated for enhancement of THz emission from the spintronic device, and its THz emission properties are evaluated.