Detecting and Switching Magnetization of Stoner Nanograin in Non-local Spin Valve

TL;DR

This paper provides a theoretical analysis of magnetization detection and switching in a nanoscale Stoner grain within a non-local spin valve, highlighting the role of spin bias and tunneling effects in the process.

Contribution

It introduces a unified rate equation framework for describing both the NLSV signal readout and the magnetization switching in ultrasmall nanograins.

Findings

Spin bias is sufficient to induce magnetization switching.

The NLSV signal is influenced by the ultrasmall size of the grain.

During reversal, a spin-polarized current may flow instead of a pure spin current.

Abstract

The magnetization detection and switching of an ultrasmall Stoner nanograin in a non-local spin valve (NLSV) device is studied theoretically. With the help of the rate equations, a unified description can be presented on the same footing for the NLSV signal that reads out the magnetization, and for the switching process. The setup can be viewed as that the grain is connected to two non-magnetic leads via sequential tunneling. In one lead, the chemical potentials for spin-up and -down electrons are split due to the spin injection in the NLSV. This splitting (or the spin bias) is crucial to the NLSV signal and the critical condition to the magnetization switching. By using the standard spin diffusion equation and parameters from recent NLSV device, the magnitude of the spin bias is estimated, and found large enough to drive the magnetization switching of the cobalt nanograin reported in earlier experiments. A microscopic interpretation of NLSV signal in the sequential tunneling regime is thereby raised, which show properties due to the ultrasmall size of the grain. The dynamics at the reversal point shows that there may be a spin-polarized current instead of the anticipated pure spin current flowing during the reversal due to the electron accumulation in the floating lead used for the readout of NLSV signal.