Observation of the spin Seebeck effect

Abstract

The generation of electric voltage by placing a conductor in a temperature gradient is called the Seebeck effect. Its efficiency is represented by the Seebeck coefficient, S, which is defined as the ratio of the generated electric voltage to the temperature difference, and is determined by the scattering rate and the density of the conduction electrons. The effect can be exploited, for example, in thermal electric-power generators and for temperature sensing, by connecting two conductors with different Seebeck coefficients, a device called a thermocouple. Here we report the observation of the thermal generation of driving power, or voltage, for electron spin: the spin Seebeck effect. Using a recently developed spin-detection technique that involves the spin Hall effect, we measure the spin voltage generated from a temperature gradient in a metallic magnet. This thermally induced spin voltage persists even at distances far from the sample ends, and spins can be extracted from every position on the magnet simply by attaching a metal. The spin Seebeck effect observed here is directly applicable to the production of spin-voltage generators, which are crucial for driving spintronic devices. The spin Seebeck effect allows us to pass a pure spin current, a flow of electron spins without electric currents, over a long distance. These innovative capabilities will invigorate spintronics research.

Efficient thermal spin injection using CoFeAl nanowire

“…Furthermore, the spin current induced by thermal spin injection is determined by the difference in the Seebeck coefficient between the up and down spins, 7,15 which is known as the spin-dependent Seebeck effect. This effect is different from the spin Seebeck effect, 6,14 although both effects produce spin current and spin accumulation from the temperature gradient. The Seebeck coefficient is strongly correlated to the band structure around the Fermi level, and under simple approximation in metals, the coefficient is proportional to the energy derivative of the logarithmic density of state (DOS) at the Fermi level.…”

“…Recently, heat has been used as a new approach to control the spin in ferromagnetic/nonmagnetic hybrid nanostructures. [6][7][8][9][10][11][12][13][14] A representative and fascinating phenomenon is thermal spin injection, in which excess heat can be used to produce spin current because of the spin-dependent Seebeck coefficient. [7][8][9] Until now, thermally driven spin injection has only been demonstrated using conventional ferromagnetic metals such as permalloy (Py) 7 and cobalt.…”

Large anomalous Nernst effect at room temperature in a chiral antiferromagnet

“…Our first-principles calculations reveal that this arises from a significantly enhanced Berry curvature associated with Weyl points near the Fermi energy 11 . As this e ect is geometrically convenient for thermoelectric power generation-it enables a lateral configuration of modules to cover a heat source 6 -these observations suggest that a new class of thermoelectric materials could be developed that exploit topological magnets to fabricate e cient, densely integrated thermopiles.Current intensive studies on thermally induced electron transport in ferromagnetic materials have opened various avenues for research on thermoelectricity and its application [12][13][14][15] . This trend has also triggered renewed interest in the anomalous Nernst effect (ANE) in ferromagnetic metals [3][4][5][6][7]15 , which is the spontaneous transverse voltage drop induced by heat current and is known to be proportional to magnetization (Fig.…”

“…Current intensive studies on thermally induced electron transport in ferromagnetic materials have opened various avenues for research on thermoelectricity and its application [12][13][14][15] . This trend has also triggered renewed interest in the anomalous Nernst effect (ANE) in ferromagnetic metals [3][4][5][6][7]15 , which is the spontaneous transverse voltage drop induced by heat current and is known to be proportional to magnetization (Fig.…”

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

“…Indeed, there is a great interest currently in spin related thermoelectric effects. One of such phenomena is the spin Seebeck effect, where longitudinal spin current and spin voltage are generated by a temperature gradient 16 . Of particular interest, however, are spin thermoelectric effects in systems with spin-orbit interaction, where a temperature gradient gives rise to transverse spin accumulation and/or spin currents.…”