Hyun Cheol Koo

Spintronics increases the functionality of information processing while seeking to overcome some of the limitations of conventional electronics. The spin-injected field effect transistor, a lateral semiconducting channel with two ferromagnetic electrodes, lies at the foundation of spintronics research. We demonstrated a spin-injected field effect transistor in a high-mobility InAs heterostructure with empirically calibrated electrical injection and detection of ballistic spin-polarized electrons

Exploiting spin transport increases the functionality of electronic devices and enables such devices to overcome physical limitations related to speed and power. Utilizing the Rashba effect at the interface of heterostructures provides promising opportunities toward the development of high-performance devices because it enables electrical control of the spin information. Herein, the focus is mainly on progress related to the two most compelling devices that exploit the Rashba effect: spin transi

The authors demonstrate fully electrical detection of spin injection in InAs quantum wells. A spin-polarized current is injected from a Ni81Fe19 thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multilayers. Injected spins accumulate and diffuse out in the 2DEG, and the spins are electrically detected by a neighboring Ni81Fe19 electrode. The observed spin diffusion length is 1.8μm at 20K. The injected spin polarization across the Ni81Fe19∕InAs interface is 1.9% at 2

The discovery of current-switchable bi-stable remanent domain configurations on small ferromagnetic islands is reported. Rectangular NiFe islands with a thickness of 50 to 100 nm and lateral dimensions on the order of several microns were imaged using magnetic force microscopy after application of 10 ns current pulses through the material. The closure configuration can be set into either the 4 or 7 domain configuration by applying positive or negative current polarity at density on the order 107

The spin field-effect transistor, an essential building block for spin information processing, shows promise for energy-efficient computing. Despite steady progress, it suffers from a low-output signal because of low spin injection and detection efficiencies. We demonstrate that this low-output obstacle can be overcome by utilizing direct and inverse spin Hall effects for spin injection and detection, respectively, without a ferromagnetic component. The output voltage of our all-electric spin Ha

The spin-FET has been realized using a semiconductor channel, but two complementary transistors analogous to n- and p-type of the conventional charge transistors have not yet been developed. We propose a complementary logic device consisting of two types of devices, namely, parallel and antiparallel spin transistors, in which the alignments of the magnetization directions of the source and the drain electrodes are parallel or antiparallel, respectively. Only one of the two transistors is conduct

Interface engineering is an effective approach to tune the magnetic properties of van der Waals (vdW) magnets and their heterostructures. The prerequisites for the practical utilization of vdW magnets and heterostructures are a quantitative analysis of their magnetic anisotropy and the ability to modulate their interfacial properties, which have been challenging to achieve with conventional methods. Here we characterize the magnetic anisotropy of Fe₃GeTe₂ layers by employin

The conditions that lead to specific domain configurations and the associated switching characteristics of small permalloy islands were studied by using magnetic force microscopy. By measuring a large number of particles, it was established that islands that have nonzero remanent moments (nonsolenoidal) exist in one of three distinct configurations, namely: (a) true single domain, (b) quasisingle domain with edge closure patterns, and (c) multidomain with nonuniform internal magnetization. The c

Gate control of spin precession is experimentally presented in an InAs quantum well with ferromagnetic spin injector and detector. The gate electric field modulates the spin–orbit interaction and spin precession. As a consequence, spin dependent conductance in the InAs channel is controlled by the gate voltage. Using ballistic spin transport theory, gate modulation results are proved to fit very well with gate voltage dependence of Rashba field strength.