In-plane magnetic surface anisotropies in Fe(110)

In-plane magnetic surface anisotropies have been detected for Fe(110) on W(110) using in situ Conversion Electron Mössbauer Spectroscopy (CEMS). The phenomenon used for the determination of this anisotropy was a switching of the spontaneous magnetizationJ _s from [001] to [1¯10] with decreasing thickness. Analysis of the data is performed using a homogeneous magnetization approximation for competing surface and bulk anisotropies, which is justified by a micromagnetic analysis and established experimentally by CEMS. In-plane surface anisotropy constants for the clean Fe(110) surface, the Fe metal-interface and the FeGaAs interface are determined toK _s,p ^FeUHV =0.065 erg·cm^–2,K _s,p ^FeMetal =0.040 erg ·cm^–2, andK _s,p ^FeGaAs =0.047 erg ·cm^–2, all with an estimated accuracy of the order of 10%.     

Multiscale modeling of submonolayer growth for Fe/Mo (110)

We use a multiscale approach to study a lattice-gas model of submonolayer growth of Fe/Mo (110) by Molecular Beam Epitaxy. To begin with, we construct a two-dimensional lattice-gas model of the Fe/Mo (110) system based on our first-principles calculations of the monomer diffusion barrier and adatom-adatom interactions. The model is investigated by equilibrium Monte Carlo (MC) simulations to compute the diffusion coefficients of Fe islands of different sizes. These diffusion coefficients are used as input to the coarse-grained kinetic rate equation (KRE) approach. We also evaluate effects of the range of Fe-Fe interaction, restriction of interaction to third nearest neighbors allowed to develop feasible atomistic kinetic Monte Carlo (KMC) model. We calculate time evolution of the island size distributions by both KMC and KRE methods and find good agreement between the two methods.     

NiO-thickness dependent magnetic anisotropies in Fe/NiO/Au(001) and Fe/NiO/MgO(001) systems

The in-plane magnetic anisotropy of Fe/NiO bilayers was studied quantitatively as a function of NiO thickness using the magneto-optical Kerr effect with a rotating field. For NiO thicker than the ordering transition thickness, the total in-plane fourfold anisotropy of the Fe layer decreases with NiO thickness in Fe/NiO/Au(001), but increases in Fe/NiO/MgO(001). Our result indicates that the exchange coupling in an Fe/NiO bilayer might induce an additional in-plane fourfold anisotropy, and the opposite thickness dependent behaviors may be attributed to the different Ni²⁺ antiferromagnetic spin orientations for NiO films grown on Au(001) and MgO(001) surfaces.     

Terahertz Radiation in the Fe/Mo Magnetic Transition

Physics of the Solid State - The terahertz radiation in the Fe/Mo magnetic transition, which occurs when pumping the upper spin subzone in the Fe/Mo interface with a high-density current, has been...     

Magnetic dichroism in angular resolved XPS on the Fe(110) surface

Magnetic dichroism has been observed in the angular distribution of Fe 2p photoemission spectra from Fe(110) surface by unpolarized Al Kα X-rays. The dichroism asymmetry varies strongly around low-index forward-scattering direction in the Fe thin film. Photoelectron diffraction theory provides explanation for these unpolarized dichroism effects, which should also be generally useful in surface magnetism studies.     

Magnetic and structural properties of Fe(110)/Ag(111) and Fe(100)/Ag(100) multilayers

A comparison of the magnetic and structural properties and growth characteristics between Fe(110)/Ag(111) and Fe(100)/Ag(100) multilayers is presented. The two types of multilayers were made of the same constituent materials but with different oricutations, allowing us to examine the interesting interplay between structure and magnetism. We found fundamentally different magnetic properties including magnetocrystalline anisotropy and surface/interface and thin film magnetism for the two types of multilayers, and their origins were discussed. Presently at the Naval Research Laboratory. Presently at Argonne National Laboratory.     

Study of the island morphology at the early stages of Fe/Mo(110) MBE growth

We present theoretical study of morphology of Fe islands grown at Mo(110) surface in submonolayer MBE mode. We utilize atomistic SOS model with bond counting, and interactions of Fe adatom up to third nearest neighbors. We performed KMC simulations for different values of adatom interactions and varying temperatures. We have found that, while for the low temperature islands are fat fractals, for the temperature 500 K islands have faceted rhombic-like shape. For the higher temperature, islands acquire a rounded shape. In order to evaluate qualitatively morphological changes, we measured average aspect ratio of islands. We calculated dependence of the average aspect ratio on the temperature, and on the strength of interactions of an adatom with neighbors.      

The ferromagnetic monolayer Fe(110) on W(110)

Ferromagnetic order in the pseudomorphic monolayer Fe(110) on W(110) was analyzed experimentally using Conversion Electron Mössbauer Spectroscopy (CEMS) and Torsion Oscillation Magnetometry (TOM). The monolayer is thermodynamically stable, crystallizes to large monolayer patches at elevated temperatures and therefore forms an excellent approximation to the ideal monolayer structure. It is ferromagnetic below a Curie-temperatureT _c,mono, which is given by (282±3) K for the Ag-coated layer, (290±10) K for coating by Cu, Ag or Au and ≈210 K for the free monolayer. For the Ag-coated monolayer, ground state hyperfine fieldB _hf (0)=(11.9±0.3) T and magnetic moment per atom μ=2.53 μ_B could be determined, in fair agreement with theoretical predictions. Unusual properties of the phase transition are detected by the combination of both experimental techniques. Strong magnetic anisotropies, which are essential for ferromagnetic order, are determined by CEMS.