Terahertz emission from α-W/CoFe epitaxial spintronic emitters

We report efficient terahertz (THz) generation in epitaxial α-W/Co_60Fe_40 spintronic emitters. Two types of emitters have been investigated; epitaxial α-W(110)/Co_60Fe_40(110) and α-W(001)/Co_60Fe_40(001) deposited on single crystalline Al_2O_3(11-20) and MgO(001) substrates, respectively. The generated THz radiation is about 10 single crystalline Al_2O_3(11-20), which is explained by the fact that the α-W(110)/Co_60Fe_40(110) interface for this emitter is more transparent to the spin current due to the presence of Angstrom-scale interface intermixing at the W/CoFe interface. Our results also reveal that the generation of THz radiation is larger when pumping with the laser light from the substrate side, which is explained by a larger part of the laser light due to interference effects in the film stack being absorbed in the ferromagnetic Co_60Fe_40 layer in this measurement configuration.