A5068060954- Magnetic properties of thin films
- Quantum and electron transport phenomena
- Semiconductor Quantum Structures and Devices
- ZnO doping and properties
- Magnetic and transport properties of perovskites and related materials
- Semiconductor materials and devices
- Electronic and Structural Properties of Oxides
- Magneto-Optical Properties and Applications
- Physics of Superconductivity and Magnetism
- Advancements in Semiconductor Devices and Circuit Design
- Advanced Memory and Neural Computing
- Heusler alloys: electronic and magnetic properties
- Photonic Crystals and Applications
- Photonic and Optical Devices
- Ferroelectric and Negative Capacitance Devices
- Quantum Dots Synthesis And Properties
- Advanced Condensed Matter Physics
- Surface and Thin Film Phenomena
- Chalcogenide Semiconductor Thin Films
- Organic Light-Emitting Diodes Research
- Semiconductor Lasers and Optical Devices
- Neural Networks and Reservoir Computing
- Conducting polymers and applications
- GaN-based semiconductor devices and materials
- Plasmonic and Surface Plasmon Research
Martin Luther University Halle-Wittenberg
2016-2025
Otto-von-Guericke University Magdeburg
2024
Yale University
2019
The Ohio State University
2019
Aalto University
2018
Luther University
2015
University of Würzburg
2003-2013
Cornell University
1970-1994
RCA (United States)
1986
University of Maryland, Baltimore
1978
We have calculated the spin-polarization effects of a current in two-dimensional electron gas which is contacted by two ferromagnetic metals. In purely diffusive regime, may indeed be spin-polarized. However, for typical device geometry degree limited to less than 0.1% only. The change resistance parallel and antiparallel magnetization contacts up quadratically smaller, will thus difficult detect.
We introduce a new class of spintronic devices in which spin-valve-like effect results from strong spin-orbit coupling single ferromagnetic layer rather than injection and detection spin-polarized current by two coupled ferromagnets. The is observed normal-metal-insulator-ferromagnetic-semiconductor tunneling device. This behavior caused the interplay anisotropic density states (Ga,Mn)As with respect to magnetization direction two-step reversal process this material.
Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in GHz-to-THz frequency range, utilization nonlinear nonreciprocal phenomena, compatibility with CMOS are just a few many advantages offered by magnons. Although magnonics is still primarily positioned academic domain, scientific technological challenges field being extensively investigated, proof-of-concept prototypes have already been realized...
We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping extremely narrow linewidth can be observed. For 56 nm thick constant α = (6.15 ± 1.50) · 10(-5) is found at 9.6 GHz as small 1.30 0.05 Oe which are lowest values for PLD...
We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic in quantum well, and studied their current-voltage characteristics. When subjected to an external field resulting spin splitting of levels well leads a transmission resonance into two separate peaks. This is interpreted as evidence transport through polarized levels, could be first step towards voltage controlled filter.
In NaF, NaI, and LiF crystals of modest chemical or isotopic purity, only ballistic diffusive propagation heat is observed. very pure NaF an additional pulse occurs. This shows the behavior incipient second sound.
Spintronics is a topic that has raised lot of interest during the past years. The transport and manipulation spin polarized electrons or holes in semiconductors offers huge potential for novel devices combine non-volatile information storage with high processing speed at low power, which may even be useful quantum computation. However, one major ingredient been missing long time transfer carriers from magnetic contact into non-magnetic semiconductor. Highly efficient electrical injection was...
The Rashba Hamiltonian describes the splitting of conduction band as a result spin-orbit coupling in presence an external field and is commonly used to model electronic structure confined narrow-gap semiconductors. Due mixing spin states some care has be exercised calculation transport properties. We derive velocity operator for Rashba-split demonstrate that transmission interface between ferromagnet semiconductor does not depend on magnetization direction, contrast with previous assertions...
Using the ultra low damping NiMnSb half-Heusler alloy patterned into vortex-state magnetic nano-dots, we demonstrate a new concept of non-volatile memory controlled by frequency. A perpendicular bias field is used to split frequency vortex core gyrotropic rotation two distinct frequencies, depending on sign polarity $p=\pm1$ inside dot. resonance force microscope and microwave pulses applied at one these resonant frequencies allow for local deterministic addressing binary information (core polarity).
It is demonstrated by SQUID measurements that (Ga,Mn)As films can exhibit perpendicular easy axis at low temperatures, even under compressive strain, provided the hole concentration sufficiently low. In such films, assumes a standard in-plane orientation when temperature raised towards Curie or increased annealing. These findings are shown to corroborate quantitatively predictions of mean-field Zener model for ferromagnetic semiconductors. The anisotropy also examined, and possible...
We have fabricated (Ga,Mn)As nanostructures in which domain walls can be pinned by sub-10 nm constrictions. Controlled shape anisotropy, we switch the regions on either side of constriction to parallel or antiparallel magnetization. All samples exhibit a positive magnetoresistance, consistent with domain-wall trapping. For metallic samples, find magnetoresistance up 8%, understood from spin accumulation. In where, due depletion at constriction, tunnel barrier is formed, observe 2000%.
We report the discovery of a very large tunneling anisotropic magnetoresistance in an epitaxially grown $(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/(\mathrm{G}\mathrm{a},\mathrm{M}\mathrm{n})\mathrm{A}\mathrm{s}$ structure. The key novel spintronics features this effect are as follows: (i) both normal and inverted spin-valve-like signals; (ii) nonhysteretic for magnetic fields perpendicular to interfaces; (iii) magnetization...
In this paper we review and extend our modelling of the physics governing electrical spin injection into non-magnetic semiconductors. A critical evaluation is given several approaches to circumvent impedance mismatch that prohibits in diffusive transport regime, i.e. ballistic transport, use tunnel barriers a Schottky contact. We conclude by discussing an experimental illustration modelling. all-electrical geometry, utilize from paramagnetic injector demonstrate novel magnetoresistance effect.
Microwave spectroscopy of individual vortex-state magnetic nanodisks in a perpendicular bias field $H$ is performed using resonance force microscope. It reveals the splitting induced by on gyrotropic frequency vortex core rotation related to existence two stable polarities core. This enables spectroscopic detection polarity. The bistability extends up large negative (antiparallel core) value ${H}_{r}$, at which polarity reversed. difference between frequencies rotational modes corresponding...
Nano resonators in which mechanical vibrations and spin waves can be coupled are an intriguing concept that used quantum information processing to transfer between different states of excitation. Until now, the fabrication free standing magnetic nanostructures host long lived wave excitatons may suitable as seemed elusive. We demonstrate monocrystalline yttrium iron garnet (YIG) 3D nanoresonators with nearly ideal properties. The freestanding structures obtained using a complex lithography...
Reliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction electric field linearly polarized pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic emitter. Polarity more than 99% contrast at rate 10 kHz achieved using harmonic field. By adding static field, between angles of, instance, −53° and 53° kilohertz rates. We believe our approach makes emitters promising source low-noise...
We obtain control of magnetic anisotropy in epitaxial (Ga,Mn)As by anisotropic strain relaxation patterned structures. The the structures is characterized using sophisticated X-ray techniques. before patterning layer, which shows biaxial easy axes along [100] and [010], replaced a hard axis direction large elastic uniaxial where pseudomorphic conditions are retained. This strong can not be explained shape attributed solely to lattice relaxation. Upon increasing stripes, we also observe an...
Abstract We have investigated the unidirectional spin wave heat conveyer effect in sub-micron thick yttrium iron garnet (YIG) films using lock-in thermography (LIT). Although is small thin layers this technique allows us to observe asymmetric transport by magnons which leads temperature profiles differing several mK on both sides of exciting antenna, respectively. Comparison Damon-Eshbach and backward volume modes shows that flow indeed due non-reciprocal spin-waves. Because finite...
Abstract We present spin pumping and inverse Hall effect (ISHE) in an epitaxial complex oxide heterostructure. Ferromagnetic La 0.7 Sr 0.3 MnO 3 (LSMO) is used as a source of while the sink exhibiting ISHE consists SrRuO (SRO). SRO ferromagnetic with metallic conductivity, however, Curie temperature ( T C ) 155 K, thus well below room temperature. This choice allows to perform experiment above demonstrate that not only shows magnitude comparable Pt (though opposite sign) its non magnetic...
A novel magnetoresistance effect, due to the injection of a spin-polarized electron current from dilute magnetic into non-magnetic semiconductor, is presented. The effect results suppression spin channel in semiconductor and can theoretically yield positive 100%, when flip length sufficiently large. Experimentally, our devices exhibit up 25% magnetoresistance.
One major challenge for the development of spintronic devices is control spin polarization an electron current. We propose and demonstrate use a BeTe/Zn1−xSe/BeTe double barrier resonant tunneling diode injection spin-polarized current into GaAs manipulation orientation injected carriers via external voltage. A up to 80% can be observed with semimagnetic layer only 3.5 nm thickness. By changing resonance condition voltage, degree varied, though complete switching has not yet been accomplished.
We report the observation of tunneling anisotropic magnetoresistance (TAMR) in an organic spin-valve-like structure with only one ferromagnetic electrode. The device is based on a new high mobility perylene diimide-based n-type semiconductor. effect originates from injection LSMO contact and can thus occur even for layers which are too thick to support assumption through layer. Magnetoresistance measurements show clear spin-valve signal, typical two step switching pattern caused by...