Carrier-induced ferromagnetism in 2D magnetically-doped semiconductor structures

TL;DR

This paper presents a theoretical model demonstrating that 2D semiconductor systems with magnetic ions can exhibit ferromagnetism at potentially room temperature, influenced by spin-orbit coupling and external control methods.

Contribution

The study introduces a new theoretical framework for ferromagnetism in 2D magnetic semiconductors, emphasizing the role of discrete symmetry and molecular field fluctuations.

Findings

Ferromagnetism can be achieved in 2D semiconductors with magnetic ions.

The Curie temperature $T_c$ depends on the chemical potential and can approach room temperature.

External control, such as gate bias, can tune magnetic properties.

Abstract

We show theoretically that the magnetic ions, randomly distributed in a two-dimensional (2D) semiconductor system, can generate a ferromagnetic long-range order via the RKKY interaction. The main physical reason is the discrete (rather than continuous) symmetry of the 2D Ising model of the spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers, which precludes the validity of the Mermin-Wagner theorem. Further, the analysis clearly illustrates the crucial role of the molecular field fluctuations as opposed to the mean field. The developed theoretical model describes the desired magnetization and phase-transition temperature $T_c$ in terms of a single parameter; namely, the chemical potential $\mu$. Our results highlight a path way to reach the highest possible $T_c$ in a given material as well as an opportunity to control the magnetic properties externally (e.g., via a gate bias). Numerical estimations show that magnetic impurities such as Mn$^{2+}$ with spins $S=5/2$ can realize ferromagnetism with $T_c$ close to room temperature.