Spin-accumulation capacitance and its application to magnetoimpedance

Abstract

It has been known that spin-dependent capacitances usually coexist with geometric capacitances in a magnetic multilayer. However, the charge and energy storage of the capacitance due to spin accumulation has not been fully understood. Here, we resolve this problem starting from the charge storage in the spin degree of freedom: spin accumulation manifests itself as an excess of electrons in one spin channel and an equal deficiency in the other under the quasi-neutrality condition. This enables us to model the two spin channels as the two plates of a capacitor. Taking a ferromagnet/nonmagnet junction as an example and using a method similar to that for treating quantum capacitance, we find that a spin-accumulation (SA) capacitance can be introduced for each layer to measure its ability to store spins. A spatial charge storage is not essential for the SA capacitor and the energy stored in it is the splitting energy of the spin-dependent chemical potentials instead of the electrostatic energy. The SA capacitance is essentially a quantum capacitance due to spin accumulation on the scale of the spin-diffusion length. The SA capacitances can be used to reinterpret the imaginary part of the low-frequency magnetoimpedance

Detection of femtosecond spin injection into a thin gold layer by time and spin resolved photoemission

“…The gold film therefore acts as a spin capacitor. The spin capacitance density 11 can be defined as the derivative Here, is the carrier density for majority and minority carriers and e is the elemental charge. In a normal metal, the density of states is independent of the spin direction.…”

“…In a normal metal, the density of states is independent of the spin direction. Therefore, it only depends on the density of states at the Fermi energy as 11 In this time-resolved experiment, we study a non-equilibrium situation: Strictly, the chemical potentials are not well-defined for the first 50 fs as the pump laser has generated a significant fraction of non-thermal electrons 33 . However, the non-thermal electrons (at least in the iron film) decay and are insignificant after 100 fs.…”

“…The number of accumulated spins per volume and the spin splitting of the chemical potentials can be seen as a spin accumulation capacitance density. This quantity has been introduced by Zhu et al 11 . The spin capacitance tells us, how much spin accumulation per volume is achieved per spin voltage unit and is the equivalent to the capacitance density in electronics.…”

Aislantes topológicos en la espintrónica

“…El concepto de capacitancia de carga es ampliamente usado en electrónica y hace referencia a la habilidad de un material para acumular carga y por lo tanto, energía. En espintrónica, Zhu et al (2017) introducen el concepto de la capacitancia de espín como la habilidad de un material de almacenar espines en vez de carga.…”

“…es la resistividad ferromagnética (noferromagnética) y α F (α N ) son parámetros adimensionales definidos en Zhu et al (2017).…”