764 research outputs found
Half-metallic diluted antiferromagnetic semiconductors
The possibility of half-metallic antiferromagnetism, a special case of
ferrimagnetism with a compensated magnetization, in the diluted magnetic
semiconductors is highlighted on the basis of the first principles electronic
structure calculation. As typical examples, the electrical and magnetic
properties of II-VI compound semiconductors doped with 3d transition metal ion
pairs--(V, Co) and (Fe, Cr)--are discussed
Velocity of domain-wall motion induced by electrical current in a ferromagnetic semiconductor (Ga,Mn)As
Current-induced domain-wall motion with velocity spanning over five orders of
magnitude up to 22 m/s has been observed by magneto-optical Kerr effect in
(Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to
verify theories of spin-transfer by the Slonczewski-like mechanism as well as
by the torque resulting from spin-flip transitions in the domain-wall region.
Evidence for domain-wall creep at low currents is found.Comment: 5 pages, 3 figure
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
CoFeB Thickness Dependence of Thermal Stability Factor in CoFeB/MgO Perpendicular Magnetic Tunnel Junctions
Thermal stability factor (delta) of recording layer was studied in
perpendicular anisotropy CoFeB/MgO magnetic tunnel junctions (p-MTJs) with
various CoFeB recording layer thicknesses and junction sizes. In all series of
p-MTJs with different thicknesses, delta is virtually independent of the
junction sizes of 48-81 nm in diameter. The values of delta increase linearly
with increasing the recording layer thickness. The slope of the linear fit is
explained well by a model based on nucleation type magnetization reversal.Comment: 12 pages, 5 figure
Domain-wall resistance in ferromagnetic (Ga,Mn)As
A series of microstructures designed to pin domain-walls (DWs) in (Ga,Mn)As
with perpendicular magnetic anisotropy has been employed to determine extrinsic
and intrinsic contributions to DW resistance. The former is explained
quantitatively as resulting from a polarity change in the Hall electric field
at DW. The latter is one order of magnitude greater than a term brought about
by anisotropic magnetoresistance and is shown to be consistent with
disorder-induced misstracing of the carrier spins subject to spatially varying
magnetization
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
MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers
The authors studied an effect of ferromagnetic (Co20Fe60B20 or Fe) layer
insertion on tunnel magnetoresistance (TMR) properties of MgO-barrier magnetic
tunnel junctions (MTJs) with CoFe/Pd multilayer electrodes. TMR ratio in MTJs
with CoFeB/MgO/Fe stack reached 67% at an-nealing temperature (Ta) of 200
degree C and then decreased rapidly at Ta over 250 degree C. The degradation of
the TMR ratio may be related to crystallization of CoFe(B) into fcc(111) or
bcc(011) texture result-ing from diffusion of B into Pd layers. MTJs which were
in-situ annealed at 350oC just after depo-siting bottom CoFe/Pd multilayer
showed TMR ratio of 78% by post annealing at Ta =200 degree C.Comment: 12 pages, 4 figure
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