Phase diagram of a ferromagnetic semiconductor. The origin of superparamagnetism

TL;DR

This paper presents an analytical study of a ferromagnetic semiconductor modeled as randomly distributed Ising spins with long-range interactions, revealing the conditions for superparamagnetism and complex phase behavior.

Contribution

It introduces an analytical approach to understanding the phase diagram and superparamagnetic state in ferromagnetic semiconductors with long-range exchange interactions.

Findings

Finite spin systems exhibit superparamagnetism below a critical magnetic field.

Analytical expressions for magnetic susceptibility and heat capacity are derived.

The phase structure of ferromagnetic semiconductors is complex and discussed in detail.

Abstract

We study the theoretical model of a ferromagnetic semiconductor as a system of randomly distributed Ising spins with a long-range exchange interaction. Using the density-of-states approach, we analytically obtain the magnetic susceptibility and heat capacity over a wide range of temperatures and magnetic fields. It is shown that the finite system of spins in magnetic field less than a certain critical field is in a superparamagnetic state due to thermodynamic fluctuations. The complex phase structure of a ferromagnetic semiconductor is discussed.