Spin battery operated by ferromagnetic resonance

Abstract

Precessing ferromagnets are predicted to inject a spin current into adjacent conductors via Ohmic contacts, irrespective of a conductance mismatch with, for example, doped semiconductors. This opens the way to create a pure spin source spin battery by the ferromagnetic resonance. We estimate the spin current and spin bias for different material combinations.Comment: The estimate for the magnitude of the spin bias is improved. We find that it is feasible to get a measurable signal of the order of the microwave frequency already for moderate rf intensitie

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

“…Intuitively, the spin accumulation can be measured electrically using a second ferromagnet as a spin-dependent contact, placed at a shorter distance compared to the spin-flip length. 10,[32][33][34] Voltage at F / N interface: Importantly, 35 have predicted a more direct way to detect the spin pump effect in which the precessing ferromagnet acts also as the detector. We have to take into account that the spin accumulation s in a diffusive metal drives the spin current I s back back into the F. The component parallel to m can enter F. Moreover, since the interface and the bulk conductances of F are spin dependent, this can result in charge accumulation, close to the interface, and thereby a dc voltage across the interface.…”

“…30,31 This equation shows that the spin current, which goes into N, is perpendicular both to the magnetization direction m and to the change of m in time. This current has ac and dc components, but in the limit N ӷ 1 ͑see later discussion͒, the time-averaged pumping current reads 10 …”

“…The total spin current in this case is I s F = I s pump + I s back . Spin battery: A spin battery operated by FMR has been proposed by Brataas et al 10 in the limit of weak spin-flip scattering in the F. The spin accumulation in N can be calculated by solving the spin-diffusion equation…”

“…This means that if the length of N is larger than l , the x, y components of spin accumulation are fully averaged ͑due to dephasing͒ and the remaining z component is constant and along the static magnetic-field direction. 10 The time-averaged spin accumulation ͗ s ͘ t = z z in the N close to the interface reads 10…”

“…This effect is the so-called spin pumping, proposed by Tserkovnyak and co-workers. 9,10 Spin pumping is a mechanism where a pure spin current, which does not involve net charge currents, is emitted at the interface between a ferromagnet with a precessing magnetization and a normal-metal region. It is an important mechanism to generate spin currents, since other electronic methods based on driving an electrical current through a ferromagnet/semiconductor interface are strongly limited by the so-called conductance mismatch.…”