23 research outputs found
Exploiting Locally Imposed Anisotropies in (Ga,Mn)As: a Non-volatile Memory Device
Progress in (Ga,Mn)As lithography has recently allowed us to realize
structures where unique magnetic anisotropy properties can be imposed locally
in various regions of a given device. We make use of this technology to
fabricate a device in which we study transport through a constriction
separating two regions whose magnetization direction differs by 90 degrees. We
find that the resistance of the constriction depends on the flow of the
magnetic field lines in the constriction region and demonstrate that such a
structure constitutes a non-volatile memory device
Experimental observation of the optical spin transfer torque
The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.Comment: 11 pages, 4 figure
Deterministic control of magnetic vortex wall chirality by electric field
Concepts for information storage and logical processing based on magnetic domain walls have great potential for implementation in future information and communications technologies. To date, the need to apply power hungry magnetic fields or heat dissipating spin polarized currents to manipulate magnetic domain walls has limited the development of such technologies. The possibility of controlling magnetic domain walls using voltages offers an energy efficient route to overcome these limitations. Here we show that a voltage-induced uniaxial strain induces reversible deterministic switching of the chirality of a magnetic vortex wall. We discuss how this functionality will be applicable to schemes for information storage and logical processing, making a significant step towards the practical implementation of magnetic domain walls in energy efficient computing
Nonvolatile ferroelectric control of ferromagnetism in (Ga,Mn)As
There is currently much interest in materials and structures that provide
coupled ferroelectric and ferromagnetic responses, with a long-term goal of
developing new memories and spintronic logic elements. Within the field there
is a focus on composites coupled by magnetostrictive and piezoelectric strain
transmitted across ferromagnetic-ferroelectric interfaces, but substrate
clamping limits the response in the supported multilayer configuration favoured
for devices. This constraint is avoided in a ferroelectric-ferromagnetic
bilayer in which the magnetic response is modulated by the electric field of
the poled ferroelectric. Here, we report the realization of such a device using
a diluted magnetic semiconductor (DMS) channel and a polymer ferroelectric
gate. Polarization reversal of the gate by a single voltage pulse results in a
persistent modulation of the Curie temperature as large as 5%. The device
demonstrates direct and quantitatively understood electric-fieldmediated
coupling in a multiferroic bilayer and may provide new routes to nanostructured
DMS materials and devices via ferroelectric domain nanopatterning. The
successful implementation of a polymer-ferroelectric gate fieldeffect
transistor (FeFET) with a DMS channel adds a new functionality to semiconductor
spintronics and may be of importance for future low-voltage spintronics devices
and memory structures.Comment: 19 pages, 5 figure
Piezo voltage controlled planar hall effect devices
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT)/ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90° in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demonstration may lead to the realization of both information storage and processing using ferromagnetic materials
Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin -films
Describing the origin of uniaxial magnetic anisotropy (UMA) is generally
problematic in systems other than single crystals. We demonstrate an in-plane
UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of
the interface anisotropy in ferromagnetic films on GaAs(001), but strength
which is independent of, rather than in inverse proportion to, the film
thickness. We show that this volume UMA is consistent with a bond-orientational
anisotropy, which propagates the interface-induced UMA through the thickness of
the amorphous film. It is explained how, in general, this mechanism may
describe the origin of in-plane UMAs in amorphous ferromagnetic films.Comment: 4 pages, 4 figure
Magnetism and carrier modulation in (Ga,Mn)As/organic-dye hybrid devices
We present the manipulation of magnetic and electrical properties of Ga,Mn As via the adsorption
of dye-molecules as a step toward the realization of light-controlled magnetic-semiconductor/dye
hybrid devices. A significant lowering of the Curie temperature with a corresponding increase in
electrical resistance and a higher coercive field is found for the Ga,Mn As/fluorescein system with
respect to Ga,Mn As. Upon exposure to visible light a shift in Curie temperature toward higher
values as well as a reduction of the electrical resistance and the coercive field can be achieved. This
points toward a hole quenching effect at the molecule- Ga,Mn As interface which is susceptible to
light exposure
Electrical transport of 2D electrons in non-uniform magnetic fields
We present a review of some of our recent experimental work on hybrid ferromagnet/semiconductor devices in which 2D electrons propagate through magnetic barriers, periodic magnetic modulations, and random magnetic fields
Magnetization reversal in trilayer structures consisting of GaMnAs layers with opposite signs of anisotropic magnetoresistance
Polarized x-ray spectroscopy of quaternary ferromagnetic semiconductor (Ga,Mn)(As,P) thin films
X-ray magnetic circular dichroism (XMCD) is used to study the magnetic and electronic properties of the quaternary diluted magnetic semiconductor (Ga,Mn)(As,P) as a function of the P concentration y. A clear signature of the variation in strain, from compressive to tensile on increasing y, is observed in the angular dependence of the hybridized d(5)-like Mn L(2,3) XMCD spectra. The ferromagnetic transition temperature and magnetic moment per Mn ion both decrease steadily with increasing y. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3609776