Spin diffusion induced by pulsed-laser heating and the role of spin heat accumulation

Abstract

We present a model for describing spin-diffusion in normal metal/ferromagnetic metal heterostructures induced by pulsed-laser heating. The model is based on the assumptions that electronic heat currents give rise to the spin-dependent Seebeck effect and that ultrafast demagnetization generates spin accumulation with a rate proportional to the demagnetization rate measured. Spin-diffusion currents are then driven by gradients in spin accumulation and electron temperature.The model considers spin-dependent thermal conductivity and electron-phonon coupling, which can give rise to different effective temperatures for majority and minority spins, known as spin heat accumulation. We find that spin heat accumulation can significantly enhance the spin-dependent Seebeck effect.

Ultrafast magnetic switching of GdFeCo with electronic heat currents

“…3b) in samples with thick Au films despite negligible direct optical absorption. Electronic charge currents play no role in our experiments because the dielectric relaxation time in metals is on the order of 10 -18 s [18].…”

Laser-induced ultrafast spin current pulses: a thermodynamic approach

“…However, the Spin-Seebeck effect can be significant at interfaces as well as at lower electron gas temper atures [21,22,36]. Neglecting the Seebeck term, equation (5) simplifies to…”

“…and majority electrons. Notice, that there can be a temperature difference between the two spin populations at the interface to the substrate [22], which is neglected in our model. The electron densities are:…”

“…The charge current density = j 0 c → vanishes due to charge neutrality and efficient screening [22] which leads to a spin current density of…”

“…The proposed spin current has been experimentally observed by several groups [16][17][18][19][20][21], offering the opportunity to generate femtosecond spin current pulses. Kimling et al [22] developed a model of laser driven spin currents generated by the spin-Seebeck effect.…”