1,998 research outputs found
Thickness dependence of magnetic properties of (Ga,Mn)As
We report on a monotonic reduction of Curie temperature in dilute
ferromagnetic semiconductor (Ga,Mn)As upon a well controlled
chemical-etching/oxidizing thinning from 15 nm down to complete removal of the
ferro- magnetic response. The effect already starts at the very beginning of
the thinning process and is accompanied by the spin reorientation transition of
the in-plane uniaxial anisotropy. We postulate that a negative gradient along
the growth direction of self-compensating defects (Mn interstitial) and the
presence of surface donor traps gives quantitative account on these effects
within the p-d mean field Zener model with adequate mod- ifications to take a
nonuniform distribution of holes and Mn cations into account. The described
here effects are of practical importance for employing thin and ultrathin
layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like
resonant tunneling devices in particular.Comment: 4 pages, 4 figures and supplementary information 2 pages, 1 figur
Ferromagnetism in (In,Mn)As Diluted Magnetic Semiconductor Thin Films Grown by Metalorganic Vapor Phase Epitaxy
In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown
using metalorganic vapor phase epitaxy (MOVPE).
Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source.
Nominally single-phase, epitaxial films were achieved with Mn content as high
as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and
higher Mn concentrations, nanometer scale MnAs precipitates were detected
within the In1-xMnxAs matrix. Magnetic properties of the films were
investigated using a superconducting quantum interference device (SQUID)
magnetometer. Room-temperature ferromagnetic order was observed in a sample
with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K
and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant
magnetization and the coercive field were small, with values of 10 emu/cm^3 and
400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is
discussed in light of the recent theory based on the formation of small
clusters of a few magnetic atoms.Comment: 5 pages, 5 figures, accepted for publication in JVST
In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films
We show, by SQUID magnetometry, that in (Ga,Mn)As films the in-plane uniaxial
magnetic easy axis is consistently associated with particular crystallographic
directions and that it can be rotated from the [-110] direction to the [110]
direction by low temperature annealing. We show that this behavior is
hole-density-dependent and does not originate from surface anisotropy. The
presence of uniaxial anisotropy as well its dependence on the
hole-concentration and temperature can be explained in terms of the p-d Zener
model of the ferromagnetism assuming a small trigonal distortion.Comment: 4 pages, 6 Postscript figures, uses revtex
Electronic and magnetic properties of GaMnAs: Annealing effects
The effect of short-time and long-time annealing at 250C on the conductivity,
hole density, and Curie temperature of GaMnAs single layers and GaMnAs/InGaMnAs
heterostructures is studied by in-situ conductivity measurements as well as
Raman and SQUID measurements before and after annealing. Whereas the
conductivity monotonously increases with increasing annealing time, the hole
density and the Curie temperature show a saturation after annealing for 30
minutes. The incorporation of thin InGaMnAs layers drastically enhances the
Curie temperature of the GaMnAs layers.Comment: 4 pages, 6 figures, submitted to Physica
Anomalous Hall effect in ferromagnetic semiconductors
We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V
semiconductors. Our theory relates the anomalous Hall conductance of a
homogeneous ferromagnet to the Berry phase acquired by a quasiparticle
wavefunction upon traversing closed paths on the spin-split Fermi surface of a
ferromagnetic state. It can be applied equally well to any itinerant electron
ferromagnet. The quantitative agreement between our theory and experimental
data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder
independent contribution to the anomalous Hall conductivity dominates in
diluted magnetic semiconductors.Comment: 4 pages, 2 figure
Growth and properties of ferromagnetic In(1-x)Mn(x)Sb alloys
We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy,
In(1-x)Mn(x)Sb, and its growth by low-temperature molecular-beam epitaxy. The
magnetic properties were investigated by direct magnetization measurements,
electrical transport, magnetic circular dichroism, and the magneto-optical Kerr
effect. These data clearly indicate that In(1-x)Mn(x)Sb possesses all the
attributes of a system with carrier-mediated FM interactions, including
well-defined hysteresis loops, a cusp in the temperature dependence of the
resistivity, strong negative magnetoresistance, and a large anomalous Hall
effect. The Curie temperatures in samples investigated thus far range up to 8.5
K, which are consistent with a mean-field-theory simulation of the
carrier-induced ferromagnetism based on the 8-band effective band-orbital
method.Comment: Invited talk at 11th International Conference on Narrow Gap
Semiconductors, Buffalo, New York, U.S.A., June 16 - 20, 200
Lithographic engineering of anisotropies in (Ga,Mn)As
The focus of studies on ferromagnetic semiconductors is moving from material
issues to device functionalities based on novel phenomena often associated with
the anisotropy properties of these materials. This is driving a need for a
method to locally control the anisotropy in order to allow the elaboration of
devices. Here we present a method which provides patterning induced anisotropy
which not only can be applied locally, but also dominates over the intrinsic
material anisotropy at all temperatures
Control of Coercivities in (Ga,Mn)As Thin Films by Small Concentrations of MnAs Nanoclusters
We demonstrate that low concentrations of a secondary magnetic phase in
(Ga,Mn)As thin films can enhance the coercivity by factors up to ~100 without
significantly degrading the Curie temperature or saturation magnetisation.
Magnetic measurements indicate that the secondary phase consists of MnAs
nanoclusters, of average size ~7nm. This approach to controlling the coercivity
while maintaining high Curie temperature, may be important for realizing
ferromagnetic semiconductor based devices.Comment: 8 pages,4 figures. accepted for publication in Appl. Phys. Let
Reorientation Transition in Single-Domain (Ga,Mn)As
We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy
fields in (Ga,Mn)As results in a magnetization reorientation transition and an
anisotropic AC susceptibility which is fully consistent with a simple single
domain model. The uniaxial and biaxial anisotropy constants vary respectively
as the square and fourth power of the spontaneous magnetization across the
whole temperature range up to T_C. The weakening of the anisotropy at the
transition may be of technological importance for applications involving
thermally-assisted magnetization switching.Comment: 4 pages, 4 figure
High-field magnetoresistance of Fe/GaAs/Fe tunnel junctions
We investigate transport through 6 to 10 nm thin epitaxial GaAs(001) barriers
sandwiched between polycrystalline iron films. Apart from a pronounced
tunneling magnetoresistance effect (TMR) at low magnetic fields we observe a
distinct negative magnetoresistance (MR) at low and a positive MR at higher
temperatures. We show that the negative MR contribution is only observed for
the ferromagnetic iron contacts but is absent if iron is replaced by copper or
gold electrodes. Possible explanations of the negative MR involve suppression
of spin-flip scattering or Zeeman splitting of the tunneling barrier.Comment: 12 pages, 4 figures, submitted to Appl. Phys. Let
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