Spintronic THz emitters based on NiCu alloys

We study THz emission from ferromagnet/nonmagnetic material (FM/NM) spintronic nanostructures in which the Ni_xCu_1-x alloy with different x is used as an FM, an NM, or both layers. The stoichiometric composition of the NiCu alloys standing at two positions (we denote it as FM or PM) is chosen so that it is ferromagnetic at room temperature in the case it is used as the FM layer, and is paramagnetic at room temperature for the NM layer. Besides, we choose the nickel ratio x close to each other for both FM and PM types of the alloy (the difference is only 10%). We show that although NiCuPM does not contain heavy metal it acts as an effective converter of spin current into the electric one in our structure showing only 2.8 times smaller efficiency than Pt. Besides, the NiCuFM alloy, despite having quite small Curie temperature (approximately 65°C), acts as an effective spin source having the efficiency only 2 times smaller than Co in similar structures. This shows up the importance of boundary matching in the spintronic THz sources. Our NiCu-based THz sources reveal a possibility of effective thermally induced control of emission of THz radiation due to a unique combination of high emission rate and relatively small Curie temperature.