Stoner Magnetism in an Inversion Layer

TL;DR

This paper investigates how considering the electron wave function's variation perpendicular to a 2D plane affects magnetic properties, revealing a lowered threshold for ferromagnetism and potential magnetic transitions in Si-MOSFETs.

Contribution

It introduces a self-consistent mean-field model that accounts for transverse wave function dependence, altering the Stoner criterion for ferromagnetism in inversion layers.

Findings

Reduced critical interaction for ferromagnetic instability.

Enhanced susceptibility leading to ferromagnetism at high densities.

Possible ferromagnetic transition near the metal-insulator boundary.

Abstract

Motivated by recent experimental work on magnetic properties of Si-MOSFETs, we report a calculation of magnetisation and susceptibility of electrons in an inversion layer, taking into account the co-ordinate dependence of electron wave function in the direction perpendicular to the plane. It is assumed that the inversion-layer carriers interact via a contact repulsive potential, which is treated at a mean-field level, resulting in a self-consistent change of profile of the wave functions. We find that the results differ significantly from those obtained in the pure 2DEG case (where no provision is made for a quantum motion in the transverse direction). Specifically, the critical value of interaction needed to attain the ferromagnetic (Stoner) instability is decreased and the Stoner criterion is therefore relaxed. This leads to an increased susceptibility and ultimately to a ferromagnetic transition deep in the high-density metallic regime. In the opposite limit of low carrier densities, a phenomenological treatment of the in-plane correlation effects suggests a ferromagnetic instability above the metal-insulator transition. Results are discussed in the context of the available experimental data.