Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs

Abstract

We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs͑001͒ and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configurationinteraction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d 5 configuration that maximizes the local Mn moment. Nanoscaling and strain significantly alter the properties of MnAs. Internal strain in the nanocrystals results in reduced p-d hybridization and enhanced ionic character of the Mn-As bonding interactions. The spatial confinement and reduced p-d hybridization in the nanocrystals lead to enhanced d-electron localization, triggering d-d electron correlations, and enhancing local Mn moments. These changes in the electronic structure of MnAs have an advantageous effect on the Curie temperature of the nanocrystals, which is measured to be remarkably higher than that of bulk MnAs.

Enhanced Ferromagnetism in Cylindrically Confined MnAs Nanocrystals Embedded in Wurtzite GaAs Nanowire Shells

“…The moderate influence of strain on the magnetic properties of MnAs both in the form of epilayers deposited on, and NCs embedded in the zinc-blende GaAs had already been noticed, but resulted in a moderate increase of T C . 26,27,28,29 The significance of our experimental findings is 2-fold. First, we show that the Curie temperature in a ferromagnetic metal MnAs can be substantially increased from the textbook 313 K to above 400 K by the adequate nanostructure engineering.…”

“…All of the previous literature reports on GaAs–MnAs hybrids concerned planar samples, with MnAs nanoinclusions embedded in the zinc-blende GaAs thin films. The moderate influence of strain on the magnetic properties of MnAs both in the form of epilayers deposited on, and NCs embedded in the zinc-blende GaAs had already been noticed, but resulted in a moderate increase of T C . − …”

Covalent Bonding-Based Adhesion Method for Rigidly Coupling Metal Nanocrystals to Metal and Metal Oxide Surfaces

“…Further, encasing particles in a strain medium is complicated by the presence of organic capping ligands that allow for slip at the material interface. , Chemical methods for removing/exchanging the surface-capping agents tend to be material-specific and often negatively impact the physical/material properties of the nanocrystals. − Direct methods, such as annealing physisorbed nanocrystals at high temperatures, can force chemical bond formation with a strain medium to develop adhesion; however, at the required temperatures, the high surface energy of the nanocrystals favors sintering into disordered islands/films. , Finally, the literature reports another route to create strain-coupled nanocrystals by embedding nanocrystals in a matrix of a second material to create differing strain environments. While these methods can be quite effective at tuning magnetic properties, the details of the magnetic changes that result are highly dependent on compatible pairings of materials. − …”