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

We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configuration-interaction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d5 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.Comment: 4 figures, 2 table

Quantum effects in linear and non-linear transport of T-shaped ballistic junction

We report low-temperature transport measurements of three-terminal T-shaped device patterned from GaAs/AlGaAs heterostructure. We demonstrate the mode branching and bend resistance effects predicted by numerical modeling for linear conductance data. We show also that the backscattering at the junction area depends on the wave function parity. We find evidence that in a non-linear transport regime the voltage of floating electrode always increases as a function of push-pull polarization. Such anomalous effect occurs for the symmetric device, provided the applied voltage is less than the Fermi energy in equilibrium

Electronic states in arsenic-decapped MnAs (1100) films grown on GaAs(001): A photoemission spectroscopy study

3 pages, 2 figures.We examine the arsenic bonding in the near-surface region of initially arsenic-capped MnAs(1100) films grown on GaAs(001) as it evolves upon arsenic decapping. Line-shape analyses of high-resolution As 3d photoelectron emission spectra recorded at room temperature RT allow us to identify electronically distinct As-bonding states associated to bulk MnAs phases, bulk arsenic, and interfacial environments. Stable MnAs phases appear to be affected by the presence of a thin arsenic coating, an effect that could be advantageously used to enhance the ferromagnetic properties of MnAs films around RTWe thank the BESSY staff for support. This work has been supported by the Spanish Ministry of Education and Science (“Ramón y Cajal” and “Materials” Programs, 2005 call and MAT2004-05348 Grant, respectively) and by the German Federal Ministry for Education and Research.Peer reviewe

Magnetic phases and anisotropy in Gd-doped GaN

In this work we present a detailed study of the magnetic properties of GaN:Gd layers with different Gd content (6x10^(15) to 1x10^(19) cm^^ (-3)) grown by reactive molecular beam epitaxy. The temperature dependence of the magnetic properties suggests the existence of at least two ferromagnetic phases with different order temperatures. The coexistence of two ferromagnetic phases is explained within the framework of the phenomenological model, introduced previously by Dhar [Phys. Rev. Lett. 94, 037205 (2005)]. The layers are also found to exhibit a magnetic anisotropy, with the hard axis along the growth direction and an easy plane parallel to the surface. Moreover, the saturation magnetization shows a dependence on the orientation of the magnetic field, which may result from the anisotropy in the polarization induced in the GaN matrix by the internal and external magnetic fields