# Spin-accumulation capacitance and its application to magnetoimpedance

## TL;DR

This paper introduces the concept of spin-accumulation capacitance, modeling spin storage as a quantum capacitance related to spin-dependent chemical potential splitting, and applies it to reinterpret magnetoimpedance.

## Contribution

It proposes a new quantum capacitance model for spin accumulation in magnetic multilayers, linking spin storage to energy splitting rather than electrostatics.

## Key findings

- Spin-accumulation capacitance can be modeled as quantum capacitance.
- Energy stored is due to chemical potential splitting, not electrostatics.
- Reinterprets low-frequency magnetoimpedance using SA capacitance.

## 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.