Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLocal Environment of Ferromagnetically Ordered Mn in Epitaxial InMnAs
43
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The magnetic properties of the ferromagnetic semiconductor In0.98Mn0.02As were characterized by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The Mn exhibits an atomic-like L2,3 absorption spectrum that indicates that the 3d states are highly localized. In addition, a large dichroism at the Mn L2,3 edge was observed from 5-300 K at an applied field of 2T. A calculated spectrum assuming atomic Mn2+ yields the best agreement with the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs and InMnAs show clear differences suggesting that the ferromagnetism observed in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of the dichroism indicates the presence of two ferromagnetic species, one with a transition temperature of 30 K and another with a transition temperature in excess of 300 K. The dichroism spectra are consistent with the assignment of the low temperature species to random substitutional Mn and the high temperature species to Mn near-neighbor pairs.
rate research
Read More
We study a ferromagnetic instability in a single-band Hubbard model on the hypercubic lattice away from half filling. Using dynamical mean-field theory with the continuous-time quantum Monte Carlo simulations based on the segment algorithm, we calculate the magnetic susceptibility in the weak and strong coupling regions systematically. We then find how ferromagnetic fluctuations are enhanced when the interaction strength and density of holes are varied. The efficiency of the double flip updates in the Monte Carlo simulations is also addressed.
The negative sign of the anomalous Nernst thermopower ($S_text{ANE}$) observed in Mn-Ga ordered alloys is an attractive property for thermoelectric applications exploiting the anomalous Nernst effect (ANE); however, its origin has not been clarified. In this study, to gain insight into the negative $S_text{ANE}$, we prepared epitaxial thin films of Mn$_{x}$Ga$_{100-x}$ with $x$ ranging from 56.2 to 71.7, and systematically investigated the structural, magnetic, and transport properties including the anomalous Hall effect (AHE) and the ANE. The measured $S_text{ANE}$ is negative for all samples and shows close to one order of magnitude difference among different compositions. Together with the measured transport properties, we were able to separate the two different contributions of the ANE, i.e., one originating from the transverse thermoelectric coefficient ($alpha_{xy}$), and the other one originating from the AHE acting on the longitudinal carrier flow induced by the Seebeck effect. Both contributions are found to be negative for all samples, while the experimentally obtained negative $alpha_{xy}$ exhibits a monotonic increase towards zero with increasing $x$, which is consistent with the tendency indicated by first-principles calculations. Our results show that the large difference in the negative $S_text{ANE}$ is mostly attributed to $alpha_{xy}$, and thus shed light on further enhancement of the ANE in Mn-based ordered alloys.
We introduce a novel method for local structure determination with a spatial resolution of the order of 0.01 Angstroem. It can be applied to materials containing clusters of exchange-coupled magnetic atoms. We use neutron spectroscopy to probe the energies of the cluster excitations which are determined by the interatomic coupling strength J. Since for most materials J is related to the interatomic distance R through a linear relation dJ/dR={alpha} (for dR/R<<1), we can directly derive the local distance R from the observed excitation energies. This is exemplified for the mixed one-dimensional paramagnetic compound CsMnxMg1 xBr3 (x=0.05, 0.10) containing manganese dimers oriented along the hexagonal c-axis. Surprisingly, the resulting Mn-Mn distances R do not vary continuously with increasing internal pressure, but lock in at some discrete values.
Molecular beam epitaxy of Fe3Si on GaAs(001) is studied in situ by grazing incidence x-ray diffraction. Layer-by-layer growth of Fe3Si films is observed at a low growth rate and substrate temperatures near 200 degrees Celsius. A damping of x-ray intensity oscillations due to a gradual surface roughening during growth is found. The corresponding sequence of coverages of the different terrace levels is obtained. The after-deposition surface recovery is very slow. Annealing at 310 degrees Celsius combined with the deposition of one monolayer of Fe3Si restores the surface to high perfection and minimal roughness. Our stoichiometric films possess long-range order and a high quality heteroepitaxial interface.
Realizing high-performance nanoelectronics requires control of materials at the nanoscale. Methods to produce high quality epitaxial graphene (EG) nanostructures on silicon carbide are known. The next step is to grow Van der Waals semiconductors on top of EG nanostructures. Hexagonal boron nitride (h-BN) is a wide bandgap semiconductor with a honeycomb lattice structure that matches that of graphene, making it ideally suited for graphene-based nanoelectronics. Here, we describe the preparation and characterization of multilayer h-BN grown epitaxially on EG using a migration-enhanced metalorganic vapor phase epitaxy process. As a result of the lateral epitaxial deposition (LED) mechanism, the grown h-BN/EG heterostructures have highly ordered epitaxial interfaces, as desired in order to preserve the transport properties of pristine graphene. Atomic scale structural and energetic details of the observed row-by-row, growth mechanism of the 2D epitaxial h-BN film are analyzed through first-principles simulations, demonstrating one-dimensional nucleation-free-energy-barrierless growth. This industrially relevant LED process can be applied to a wide variety of van der Waals materials.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
