MnAs dots grown on GaN(0001)-(1x1) surface

TL;DR

This study investigates the growth, electronic structure, and magnetic properties of MnAs dots on GaN(0001) surfaces, revealing two distinct growth procedures produce different electronic and magnetic behaviors, including one with potential half-metallicity and high Curie temperature.

Contribution

It demonstrates how different growth methods of MnAs on GaN influence their electronic structure and magnetic properties, including the potential realization of half-metallic MnAs.

Findings

MnAs dots form spontaneously above 5 ML thickness.

Electronic structures differ markedly between growth methods.

One method yields MnAs with Curie temperature above room temperature.

Abstract

MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1$\cdot 10^{11}$ cm$^{-2}$ and $2.5\cdot 10^{11}$ cm$^{-2}$, respectively (as observed by AFM), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d - related contribution to the total density of states (DOS) distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both system behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intra-dot Curie temperatures substantially different. The intra-dot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.