Formation process and superparamagnetic properties of (Mn,Ga)As nanocrystals in GaAs fabricated by annealing of (Ga,Mn)As layers with low Mn content

TL;DR

This study investigates the formation and magnetic properties of Mn-rich (Mn,Ga)As nanocrystals embedded in GaAs, revealing superparamagnetic behavior and weak inter-nanocrystal coupling through structural and magnetization analyses.

Contribution

It demonstrates the formation of cubic and hexagonal (Mn,Ga)As nanocrystals in GaAs after annealing and characterizes their superparamagnetic properties, providing new insights into their magnetic behavior.

Findings

Nanocrystals form at annealing temperatures as low as 400°C.

Both cubic and hexagonal nanocrystals coexist with diameters of 7-10 nm.

Nanocrystals exhibit superparamagnetic properties with no spin-glass dynamics.

Abstract

X-ray diffraction, transmission electron microscopy, and magnetization measurements are employed to study the structural and magnetic properties of Mn-rich (Mn,Ga)As nanocrystals embedded in GaAs. These nanocomposites are obtained by moderate (400C) and high temperature (560 and 630C) annealing of (Ga,Mn)As layers with Mn concentrations between 0.1 and 2%, grown by molecular beam epitaxy at 270oC. Decomposition of (Ga,Mn)As is already observed at the lowest annealing temperature of 400C for layers with initial Mn content of 1% and 2%. Both cubic and hexagonal (Mn,Ga)As nanocrystals, with similar diameters of 7 - 10 nm are observed to coexist in layers with an initial Mn content of 0.5% after higher temperature annealing. Measurements of magnetization relaxation in the time span 0.1 - 10 000 s provide evidence for superparamagnetic properties of the (Mn,Ga)As nanocrystals, as well as for the absence of spin-glass dynamics. These findings point to weak coupling between nanocrystals even in layers with the highest nanocrystal density.