Thermodynamic and thermoelectric properties of (Ga,Mn)As and related compounds

TL;DR

This paper presents a theoretical analysis of thermodynamic and thermoelectric properties of (Ga,Mn)As, showing consistency with experimental data and arguing against the presence of an impurity band at the Fermi energy.

Contribution

The study introduces a model that accurately describes magnetic specific heat, thermoelectric power, and conductance variations in (Ga,Mn)As, challenging the impurity band hypothesis.

Findings

Magnetic specific heat behavior near T_C matches the model.

Thermoelectric power aligns with expected hole mobility dependencies.

Conductance variations at low temperatures are explained without impurity band enhancement.

Abstract

Various experimental results providing information on thermodynamic density of states in (Ga,Mn)As are analyzed theoretically assuming that holes occupy GaAs-like valence bands. Allowing for Gaussian fluctuations of magnetization, the employed model describes correctly a critical behavior of magnetic specific heat found experimentally in (Ga,Mn)As near the Curie temperature T_C [S. Yuldashev et al., Appl. Phys. Express 3, 073005 (2010)]. The magnitudes of room temperature thermoelectric power, as measured for GaAs:Be and (Ga,Mn)As [M. A. Mayer et al., Phys. Rev. B 81, 045205 (2010)], are consistent with the model for the expected energy dependencies of the hole mobility. The same approach describes also temperature variations of conductance specific to the Anderson-Mott localization, found for various dimensionality (Ga,Mn)As nanostructures at subkelvin temperatures [D. Neumaier et al., Phys. Rev. Lett. 103, 087203 (2009)]. We conclude that the examined phenomena do not provide evidence for an enhancement of density of states by the presence of an impurity band at the Fermi energy in ferromagnetic (Ga,Mn)As. Furthermore, we provide for (Ga,Mn)As expected values of both electronic specific heat at low temperatures T << T_C and magnetization as a function of the magnetic field at T_C.