Spintronic THz Emitters Based on NiCu Alloys

We study terahertz (THz) emission from ferromagnetic/nonmagnetic (FM/NM) material spintronic nanostructures in which the Ni_xCu_1-x alloy with different x is used as the FM layer, the NM layer, or both. The stoichiometric composition of the NiCu alloys located at two positions (we denote them as FM and PM) is chosen so that it is FM at room temperature when used as the FM layer and paramagnetic (PM) at room temperature when used as the NM layer. Moreover, we choose the nickel ratio x to be close for both FM and PM types of the alloy (the difference is only 10%). We show that although NiCuPM contains no heavy metal, it acts as an effective converter of spin current into charge current in our structure, exhibiting only 2.8 times lower efficiency than Pt. Furthermore, the NiCuFM alloy, despite having a relatively low Curie temperature (approximately 65 °C), serves as an effective spin source, with an efficiency only twice as low as that of Co in similar structures. This highlights the importance of boundary matching in spintronic THz sources. Our NiCu-based THz sources reveal the possibility of effective thermally induced control of THz radiation emission, enabled by a unique combination of high emission rate and relatively small Curie temperature.