53 research outputs found
Domain-wall dynamics at micropatterned constrictions in ferromagnetic (Ga,Mn)As epilayers
The influence of sub-µm geometric constrictions on 90° magnetic domain-wall nucleation and propagation in stripes of ferromagnetic (Ga0.95,Mn0.05)As was explored. Measurements of the magnetic switching behavior were performed during ramping of an external magnetic field at constant rate and at constant field in the time domain. Demagnetizing fields are found to play a crucial role in the switching behavior around the region of the constriction. Depending on the sample's initial magnetization the constriction can either assist domain-wall nucleation or hinder its propagation
Magnetotransport properties of strained Ga0.95Mn0.05As epilayers close to the metal-insulator transition: Description using Aronov-Altshuler three-dimensional scaling theory
The magnitude of the anisotropic magnetoresistance (AMR) and the longitudinal resistance in compressively strained Ga0.95Mn0.05As epilayers were measured down to temperatures as low as 30 mK. Below temperatures of 3 K, the conductivity decreases [proportional]T^1/3 over 2 orders of magnitude in temperature. The conductivity can be well described within the framework of a three-dimensional scaling theory of Anderson's transition in the presence of spin scattering in semiconductors. It is shown that the samples are on the metallic side but very close to the metal-insulator transition. At lowest temperatures, a decrease in the AMR effect is observed, which is assigned to changes in the coupling between the remaining itinerant carriers and the local Mn 5/2-spin moments
Magnetism of Fe clusters and islands on Pt surfaces
Clusters and islands of Fe atoms have been prepared by noble gas buffer layer assisted growth as well as by standard molecular beam epitaxy on Pt substrates. Xe buffer layers have been utilized to promote the formation of compact, relaxed Fe clusters with narrow size distribution. Without the Xe buffer, strained Fe islands with a characteristic misfit dislocation network are formed. Magnetization loops obtained by magneto-optical Kerr effect measurements reveal that in-plane easy magnetization axis is only found for the relaxed clusters, pointing out the important role of epitaxial lattice deformations for the magnetic anisotropy
Temperature dependent Neel wall dynamics in GaMnAs/GaAs
Extensive Kerr microscopy studies reveal a strongly temperature dependent
domain wall dynamics in Hall-bars made from compressively strained GaMnAs.
Depending on the temperature magnetic charging of domain walls is observed and
nucleation rates depend on the Hall-geometry with respect to the crystal axes.
Above a critical temperature where a biaxial-to-uniaxial anisotropy transition
occurs a drastic increase of nucleation events is observed. Below this
temperature, the nucleation of domains tends to be rather insensitive to
temperature. This first spatially resolved study of domain wall dynamics in
patterned GaMnAs at variable temperatures has important implications for
potential single domain magneto-logic devices made from ferromagnetic
semiconductors.Comment: Figures 2 and 6 not correctly TeXifie
The Physics of Kondo Impurities in Graphene
This article summarizes our understanding of the Kondo effect in graphene,
primarily from a theoretical perspective. We shall describe different ways to
create magnetic moments in graphene, either by adatom deposition or via
defects. For dilute moments, the theoretical description is in terms of
effective Anderson or Kondo impurity models coupled to graphene's Dirac
electrons. We shall discuss in detail the physics of these models, including
their quantum phase transitions and the effect of carrier doping, and confront
this with existing experimental data. Finally, we point out connections to
other quantum impurity problems, e.g., in unconventional superconductors,
topological insulators, and quantum spin liquids.Comment: 27 pages, 8 figs. Review article prepared for Rep. Prog. Phys. ("key
issues" section). (v2) Final version as publishe
Structure and magnetism of atomically thin Fe layers on flat and vicinal Pt surfaces
Ultrathin Fe films on Pt substrates have been investigated under ultrahigh vacuum conditions by scanning tunneling microscopy, low energy electron diffraction, magneto-optical Kerr effect, x-ray magnetic circular dichroism measurements, and Kerr microscopy. We present a comparison between Fe films on flat Pt(111) and stepped Pt(997), with particular focus on the magnetic anisotropy in the submonolayer thickness range below 0.2 monolayer coverage, and above the spin reorientation transition at 3 monolayer thickness. The comparison of structure and magnetism suggests that the perpendicular easy axis found for films thinner than three monolayers is due to dominating contributions from both film interfaces to the anisotropy energy. The Fe-Pt interface contribution has its origin in the hybridization of the Fe 3d with the Pt 5d band. The in-plane magnetic anisotropy above 3 atomic layers film thickness can be correlated directly with peculiarities of the film structure
Cobalt nanoclusters on metal-supported Xe monolayers: Influence of the substrate on cluster formation kinetics and magnetism
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