Observation of the spin-Seebeck effect in a ferromagnetic semiconductor

Abstract

Reducing the heat generated in traditional electronics is a chief motivation for the development of spin-based electronics, called spintronics. Spin-based transistors that do not strictly rely on the raising or lowering of electrostatic barriers can overcome scaling limits in charge-based transistors. Spin transport in semiconductors might also lead to dissipation-less information transfer with pure spin currents. Despite these thermodynamic advantages, little experimental literature exists on the thermal aspects of spin transport in solids. A recent and surprising exception was the discovery of the spin-Seebeck effect, reported as a measurement of a redistribution of spins along the length of a sample of permalloy (NiFe) induced by a temperature gradient. This macroscopic spatial distribution of spins is, surprisingly, many orders of magnitude larger than the spin diffusion length, which has generated strong interest in the thermal aspects of spin transport. Here, the spin-Seebeck effect is observed in a ferromagnetic semiconductor, GaMnAs, which allows flexible design of the magnetization directions, a larger spin polarization, and measurements across the magnetic phase transition. This effect is observed even in the absence of longitudinal charge transport. The spatial distribution of spin currents is maintained across electrical breaks, highlighting the local nature of this thermally driven effect.

Tunneling magnetothermopower in magnetic tunnel junctions

“…More recently, Gravier et al measured spin-dependent heat transport across Co/Cu multilayers [6,7]. However, the field came to prominence with the discovery of the so called spin-Seebeck effect [8][9][10][11][12].…”

“…When the spin degree of freedom is taken into account, in addition to the charge voltage, a spin accumulation might also be induced in the system. Analogously, the spin-Seebeck coefficient measures the magnitude of a spin accumulation induced by the temperature gradient [8][9][10][11][12]. Furthermore, when dealing with spin-valves, it is commonly studied the dependence of the thermopower on the relative magnetization orientations, which has been dubbed the magneto-Seebeck effect [14,21].…”

Intrinsic contribution to spin Hall and spin Nernst effects in a bilayer graphene

“…Nernst effects [17][18][19] , which correspond to the anomalous and spin Hall effects induced by longitudinal electric field. Similarity of the spin Hall and spin Nernst effects in nonmagnetic systems with spin-orbit interaction is presented in Fig.1, which clearly shows that the SHE is generated by external electric field, while the spin Nernst effect (SNE) is a similar effect generated by a temperature gradient instead of electric field (gradient of electrostatic potential).…”

Theory of thermal spin-charge coupling in electronic systems

“…It has also been observed in ferromagnetic insulators 29 as well as in the ferromagnetic semiconductor (Ga,Mn)As. 32 This suggests that the spin Seebeck effect does not need to be connected with charge flow. In (Ga,Mn)As, the sample was even cut preventing charge redistribution over the whole slab; the spin Seebeck signals were unaffected and in both cases, of compact and disconnected samples, the Pt stripes pick up the same inverse spin Hall signals.…”