598 research outputs found
Effect of n+-GaAs thickness and doping density on spin injection of GaMnAs/n+-GaAs Esaki tunnel junction
We investigated the influence of n+-GaAs thickness and doping density of
GaMnAs/n+-GaAs Esaki tunnel junction on the efficiency of the electrical
electron spin injection. We prepared seven samples of GaMnAs/n+-GaAs tunnel
junctions with different n+-GaAs thickness and doping density grown on
identical p-AlGaAs/p-GaAs/n-AlGaAs light emitting diode (LED) structures.
Electroluminescence (EL) polarization of the surface emission was measured
under the Faraday configuration with external magnetic field. All samples have
the bias dependence of the EL polarization, and higher EL polarization is
obtained in samples in which n+-GaAs is completely depleted at zero bias. The
EL polarization is found to be sensitive to the bias condition for both the
(Ga,Mn)As/n+-GaAs tunnel junction and the LED structure.Comment: 4pages, 4figures, 1table, To appear in Physica
Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction
Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.Comment: 16 pages, 4 figure
Electronic States and Magnetism of Mn Impurities and Dimers in Narrow-Gap and Wide-Gap III-V Semiconductors
Electronic states and magnetic properties of single impurity and dimer
doped in narrow-gap and wide-gap - semiconductors have been studied
systematically. It has been found that in the ground state for single
impurity, - complex is antiferromagnetic (AFM) coupling when -
hybridization is large and both the hole level and the
impurity level are close to the midgap; or very weak ferromagnetic (FM)
when is small and both and are deep in the valence band.
In dimer situation, the spins are AFM coupling for half-filled or
full-filled orbits; on the contrast, the Mn spins are double-exchange-like
FM coupling for any -orbits away from half-filling. We propose the strong
{\it p-d} hybridized double exchange mechanism is responsible for the FM order
in diluted - semiconductors
Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer
We investigated the relationship between tunnel magnetoresistance (TMR) ratio
and the crystallization of CoFeB layers through annealing in magnetic tunnel
junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet
pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased
with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C,
whereas the TMR ratio of the MTJs with pinned layers without Ru spacers
decreased at Ta over 325C. Ruthenium spacers play an important role in forming
an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through
annealing at high temperatures.Comment: 10 pages, 5 figures, submitted to Applied Physics Letter
Self-compensation in manganese-doped ferromagnetic semiconductors
We present a theory of interstitial Mn in Mn-doped ferromagnetic
semiconductors. Using density-functional theory, we show that under the
non-equilibrium conditions of growth, interstitial Mn is easily formed near the
surface by a simple low-energy adsorption pathway. In GaAs, isolated
interstitial Mn is an electron donor, each compensating two substitutional Mn
acceptors. Within an impurity-band model, partial compensation promotes
ferromagnetic order below the metal-insulator transition, with the highest
Curie temperature occurring for 0.5 holes per substitutional Mn.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Anomalous Hall effect in field-effect structures of (Ga,Mn)As
The anomalous Hall effect in metal-insulator-semiconductor structures having
thin (Ga,Mn)As layers as a channel has been studied in a wide range of Mn and
hole densities changed by the gate electric field. Strong and unanticipated
temperature dependence, including a change of sign, of the anomalous Hall
conductance has been found in samples with the highest Curie
temperatures. For more disordered channels, the scaling relation between
and , similar to the one observed previously for
thicker samples, is recovered.Comment: 5 pages, 5 figure
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
Hydrogen patterning of Ga1-xMnxAs for planar spintronics
We demonstrate two patterning techniques based on hydrogen passivation of
Ga1-xMnxAs to produce isolated ferromagnetically active regions embedded
uniformly in a paramagnetic, insulating host. The first method consists of
selective hydrogenation of Ga1-xMnxAs by lithographic masking. Magnetotransport
measurements of Hall-bars made in this manner display the characteristic
properties of the hole-mediated ferromagnetic phase, which result from good
pattern isolation. Arrays of Ga1-xMnxAs dots as small as 250 nm across have
been realized by this process. The second process consists of blanket
hydrogenation of Ga1-xMnxAs followed by local reactivation using confined
low-power pulsed-laser annealing. Conductance imaging reveals local electrical
reactivation of micrometer-sized regions that accompanies the restoration of
ferromagnetism. The spatial resolution achievable with this method can
potentially reach <100 nm by employing near-field laser processing. The high
spatial resolution attainable by hydrogenation patterning enables the
development of systems with novel functionalities such as lateral
spin-injection as well as the exploration of magnetization dynamics in
individual and coupled structures made from this novel class of semiconductors.Comment: ICDS-24, July 2007. 8 pages with 4 figure
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