Spintronic THz emitters based on NiCu alloys

TL;DR

This study demonstrates that NiCu alloys can serve as efficient spintronic THz emitters, with tunable magnetic properties and effective spin-to-charge conversion, offering potential for thermally controlled THz emission.

Contribution

It introduces NiCu alloys as versatile materials for spintronic THz emitters, showing comparable efficiency to heavy metals despite lacking heavy metal elements.

Findings

NiCu[PM] acts as an effective spin current converter with 2.8 times smaller efficiency than Pt.

NiCu[FM] functions as a spin source with efficiency twice that of Co.

Thermally induced control of THz emission is possible with NiCu alloys.

Abstract

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 NiCu[PM] 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 NiCu[FM] alloy, despite having quite small Curie temperature (approximately $65 ^\circ C$), 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.