1,236 research outputs found
Perpendicular magnetic anisotropy in bulk and thin-film CuMnAs for antiferromagnetic memory applications
CuMnAs with perpendicular magnetic anisotropy is proposed as an active
material for antiferromagnetic memory. Information can be stored in the
antiferromagnetic domain state, while writing and readout can rely on the
existence of the surface magnetization. It is predicted, based on
first-principles calculations, that easy-axis anisotropy can be achieved in
bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This
effect is attributed to the changing occupation of certain electronic bands
near the Fermi level induced by the hole doping. The calculated temperature
dependence of the magnetic anisotropy does not exhibit any anomalies. Thin
CuMnAs(001) films are also predicted to have perpendicular magnetic anisotropy.Comment: 5 pages, 8 figure
Origin of spin reorientation transitions in antiferromagnetic MnPt-based alloys
Antiferromagnetic MnPt exhibits a spin reorientation transition (SRT) as a
function of temperature, and off-stoichiometric Mn-Pt alloys also display SRTs
as a function of concentration. The magnetocrystalline anisotropy in these
alloys is studied using first-principles calculations based on the coherent
potential approximation and the disordered local moment method. The anisotropy
is fairly small and sensitive to the variations in composition and temperature
due to the cancellation of large contributions from different parts of the
Brillouin zone. Concentration and temperature-driven SRTs are found in
reasonable agreement with experimental data. Contributions from specific
band-structure features are identified and used to explain the origin of the
SRTs.Comment: 6 pages, 8 figure
Stochastic Cluster Series expansion for quantum spin systems
In this paper we develop a cluster-variant of the Stochastic Series expansion
method (SCSE). For certain systems with longer-range interactions the SCSE is
considerably more efficient than the standard implementation of the Stochastic
Series Expansion (SSE), at low temperatures. As an application of this method
we calculated the T=0-conductance for a linear chain with a (diagonal) next
nearest neighbor interaction.Comment: 5 pages, 7 figure
Phase stability, ordering tendencies, and magnetism in single-phase fcc Au-Fe nanoalloys
Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but
L1 and L1 orderings were reported in single-phase Au-Fe nanoparticles.
Motivated by these observations, we study the structural and ordering
energetics in this alloy by combining density functional theory (DFT)
calculations with effective Hamiltonian techniques: a cluster expansion with
structural filters, and the configuration-dependent lattice deformation model.
The phase separation tendency in Au-Fe persists even if the fcc-bcc
decomposition is suppressed. The relative stability of disordered bcc and fcc
phases observed in nanoparticles is reproduced, but the fully ordered L1
AuFe, L1 AuFe, and L1 AuFe structures are unstable in DFT.
However, a tendency to form concentration waves at the corresponding [001]
ordering vector is revealed in nearly-random alloys in a certain range of
concentrations. This incipient ordering requires enrichment by Fe relative to
the equiatomic composition, which may occur in the core of a nanoparticle due
to the segregation of Au to the surface. Effects of magnetism on the chemical
ordering are also discussed.Comment: 23 pages, 11 figure
Irreversible Magnetization Deep in the Vortex-Liquid State of a 2D Superconductor at High Magnetic Fields
The remarkable phenomenon of weak magnetization hysteresis loops, observed
recently deep in the vortex-liquid state of a nearly two-dimensional (2D)
superconductor at low temperatures, is shown to reflect the existence of an
unusual vortex-liquid state, consisting of collectively pinned crystallites of
easily sliding vortex chains.Comment: 5 pages, 4 figure
Interplay of the exciton and electron-hole plasma recombination on the photoluminescence dynamics in bulk GaAs
We present a systematic study of the exciton/electron-hole plasma
photoluminescence dynamics in bulk GaAs for various lattice temperatures and
excitation densities. The competition between the exciton and electron-hole
pair recombination dominates the onset of the luminescence. We show that the
metal-to-insulator transition, induced by temperature and/or excitation
density, can be directly monitored by the carrier dynamics and the
time-resolved spectral characteristics of the light emission. The dependence on
carrier density of the photoluminescence rise time is strongly modified around
a lattice temperature of 49 K, corresponding to the exciton binding energy (4.2
meV). In a similar way, the rise-time dependence on lattice temperature
undergoes a relatively abrupt change at an excitation density of 120-180x10^15
cm^-3, which is about five times greater than the calculated Mott density in
GaAs taking into account many body corrections.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
- …