Joe Barker
Studying magnetic insulator / heavy metal bilayers using femtosecond laser heating allows us to probe spin-charge conversion at interfaces. The time scale of the heating is too fast to establish long ranged thermal gradients and the spin transport these would create through the spin Seebeck effect. In this work we studied the terahertz emissions from antiferromagnetic insulator / heavy metal bilayers heated with a terahertz laser pulse [1]. We show the terahertz emission is consistent with the symmetry of a spin current being converted to a charge current via the spin Hall effect. The amplitude is proportional to the applied field which is required to split the degenerate magnon modes in the antiferromagnet. We compare measurements on two antiferromagnetic insulators, KCoF3 and KNiF3 which have the same magnetic configuration and are both good Heisenberg antiferromagnets. However, KCoF3 has a much larger magnetic anisotropy than KNiF3. We studied the temperature dependence of the terahertz emission and found it to be remarkably different in the two antiferromagnets, with a significant suppression of the signal at low temperatures for KCoF3. We model the electron-magnon scattering at the interface [2]. We find a good agreement with the experiments and find the magnon band gap plays an important role in the observed behaviour due to the absence of magnon states for electrons to scatter into.
References:
[1] F.N. Kholid et al., The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures, Nat. Commun. 14, 538 (2023).
[2] E.G. Tveten et al., Electron-magnon scattering in magnetic heterostructures far out of equilibrium, Phys. Rev. B 92, 180412 (2015)