Abstract
Terahertz emission spectroscopy (TES) of ultrathin multilayers of magnetic and heavy metals has recently attracted much interest. This method not only provides fundamental insights into photoinduced spin transport and spin–orbit interaction at highest frequencies, but has also paved the way for applications such as efficient and ultrabroadband emitters of terahertz (THz) electromagnetic radiation. So far, predominantly standard ferromagnetic materials have been exploited. Here, by introducing a suitable figure of merit, we systematically compare the strength of THz emission from [Formula: see text]/Pt bilayers with [Formula: see text] being a complex ferro-, ferri- and antiferromagnetic metal, that is, dysprosium cobalt (DyCo5), gadolinium iron (Gd[Formula: see text]Fe[Formula: see text]), magnetite (Fe3O4) and iron rhodium (FeRh). We find that the performance in terms of spin-current generation not only depends on the spin polarization of the magnet’s conduction electrons, but also on the specific interface conditions, thereby suggesting TES to be a highly interface-sensitive technique. In general, our results are relevant for all applications that rely on the optical generation of ultrafast spin currents in spintronic metallic multilayers.
Highlights
Exploiting the electron's spin degree of freedom is envisioned to be of central importance for future information technology.1 In spintronic devices, the building blocks are related to the e±cient generation, conduction and detection of spin currents
Metallic ferrimagnetic alloys consisting of rare-earth (RM) and transition metal (TM) elements, such as DyCo5 and Gd24Fe76, have been among therst magnetic media used for high-density magnetooptical recording
The all-optical magnetization switching phenomenon has been discovered on these ferrimagnets,19–21 which has brought this class of RM–TM alloys into the focus of ultrafast magnetic studies over the last years
Summary
Exploiting the electron's spin degree of freedom is envisioned to be of central importance for future information technology. In spintronic devices, the building blocks are related to the e±cient generation, conduction and detection of spin currents. The SDSE/SSE describes, respectively, the generation of a spin current carried by conduction electrons/magnons along a temperature gradient in a magnetically ordered solid. Upon illumination of ferromagnetic (FM)/nonmagnetic (NM) heterostructures with femtosecond near-infrared laser pulses, a combination of the SDSE/SSE and the subsequent ISHE gives rise to the emission of electromagnetic radiation with frequencies extending into the THz range [see Fig. 1(a)]. Besides such material-science-driven interest, spintronic heterostructures show a large potential as e±cient and broadband THz emitters. Magnetite (Fe3O4), (anti-) FM iron rhodium (FeRh), and the ferrimagnetic alloys dysprosium cobalt (DyCo5) and gadolinium iron (Gd24Fe76)
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