Additive roles of antiferromagnetically coupled elements in the magnetic proximity effect in the GdFeCo/Pt system.

Interfacial magnetic interactions between different elements are the origin of various spin-transport phenomena in multi-elemental magnetic systems. We investigate the coupling between the magnetic moments of the rare-earth, transition-metal, and heavy-metal elements across the interface in a GdFeCo/Pt thin film, an archetype system to investigate ferrimagnetic spintronics. The Pt magnetic moments induced by the antiferromagnetically aligned FeCo and Gd moments are measured using element-resolved x-ray measurements. It is revealed that the proximity-induced Pt magnetic moments are always aligned parallel to the FeCo magnetic moments, even below the ferrimagnetic compensation temperature where FeCo has a smaller moment than Gd. This is understood by a theoretical model showing distinct effects of the rare-earth Gd 4f and transition-metal FeCo 3d magnetic moments on the Pt electronic states. In particular, the Gd and FeCo work in-phase to align the Pt moment in the same direction, despite their antiferromagnetic configuration. The unexpected additive roles of the two antiferromagnetically coupled elements exemplify the importance of detailed interactions among the constituent elements in understanding magnetic and spintronic properties of thin film systems.

Voltage control of magnetism in Fe3-xGeTe2/In2Se3 van der Waals ferromagnetic/ferroelectric heterostructures.

We investigate the voltage control of magnetism in a van der Waals (vdW) heterostructure device consisting of two distinct vdW materials, the ferromagnetic Fe3-xGeTe2 and the ferroelectric In2Se3. It is observed that gate voltages applied to the Fe3-xGeTe2/In2Se3 heterostructure device modulate the magnetic properties of Fe3-xGeTe2 with significant decrease in coercive field for both positive and negative voltages. Raman spectroscopy on the heterostructure device shows voltage-dependent increase in the in-plane In2Se3 and Fe3-xGeTe2 lattice constants for both voltage polarities. Thus, the voltage-dependent decrease in the Fe3-xGeTe2 coercive field, regardless of the gate voltage polarity, can be attributed to the presence of in-plane tensile strain. This is supported by density functional theory calculations showing tensile-strain-induced reduction of the magnetocrystalline anisotropy, which in turn decreases the coercive field. Our results demonstrate an effective method to realize low-power voltage-controlled vdW spintronic devices utilizing the magnetoelectric effect in vdW ferromagnetic/ferroelectric heterostructures.

Investigation of the mechanism of the anomalous Hall effects in Cr2Te3/(BiSb)2(TeSe)3 heterostructure.

The interplay between ferromagnetism and the non-trivial topology has unveiled intriguing phases in the transport of charges and spins. For example, it is consistently observed the so-called topological Hall effect (THE) featuring a hump structure in the curve of the Hall resistance (Rxy) vs. a magnetic field (H) of a heterostructure consisting of a ferromagnet (FM) and a topological insulator (TI). The origin of the hump structure is still controversial between the topological Hall effect model and the multi-component anomalous Hall effect (AHE) model. In this work, we have investigated a heterostructure consisting of BixSb2-xTeySe3-y (BSTS) and Cr2Te3 (CT), which are well-known TI and two-dimensional FM, respectively. By using the so-called "minor-loop measurement", we have found that the hump structure observed in the CT/BSTS is more likely to originate from two AHE channels. Moreover, by analyzing the scaling behavior of each amplitude of two AHE with the longitudinal resistivities of CT and BSTS, we have found that one AHE is attributed to the extrinsic contribution of CT while the other is due to the intrinsic contribution of BSTS. It implies that the proximity-induced ferromagnetic layer inside BSTS serves as a source of the intrinsic AHE, resulting in the hump structure explained by the two AHE model.

Tuning of Thermoelectric Properties of MoSe2 Thin Films Under Helium Ion Irradiation.

Transition metal dichalcogenides have attracted renewed interest for use as thermoelectric materials owing to their tunable bandgap, moderate Seebeck coefficient, and low thermal conductivity. However, their thermoelectric parameters such as Seebeck coefficient, electrical conductivity, and thermal conductivity are interdependent, which is a drawback. Therefore, it is necessary to find a way to adjust one of these parameters without affecting the other parameters. In this study, we investigated the effect of helium ion irradiation on MoSe2 thin films with the objective of controlling the Seebeck coefficient and electrical conductivity. At the optimal irradiation dose of 1015 cm-2, we observed multiple enhancements of the power factor resulting from an increase in the electrical conductivity, with slight suppression of the Seebeck coefficient. Raman spectroscopy, X-ray diffraction, and transmission electron microscopy analyses revealed that irradiation-induced selenium vacancies played an important role in changing the thermoelectric properties of MoSe2 thin films. These results suggest that helium ion irradiation is a promising method to significantly improve the thermoelectric properties of two-dimensional transition metal dichalcogenides. Effect of He+ irradiation on thermoelectric properties of MoSe2 thin films.

Ultrafast Triggering of Insulator-Metal Transition in Two-Dimensional VSe2.

The transition-metal dichalcogenide VSe2 exhibits an increased charge density wave transition temperature and an emerging insulating phase when thinned to a single layer. Here, we investigate the interplay of electronic and lattice degrees of freedom that underpin these phases in single-layer VSe2 using ultrafast pump-probe photoemission spectroscopy. In the insulating state, we observe a light-induced closure of the energy gap, which we disentangle from the ensuing hot carrier dynamics by fitting a model spectral function to the time-dependent photoemission intensity. This procedure leads to an estimated time scale of 480 fs for the closure of the gap, which suggests that the phase transition in single-layer VSe2 is driven by electron-lattice interactions rather than by Mott-like electronic effects. The ultrafast optical switching of these interactions in SL VSe2 demonstrates the potential for controlling phase transitions in 2D materials with light.

Tunable Wetting Property in Growth Mode-Controlled WS2 Thin Films.

We report on a thickness-dependent wetting property of WS2/Al2O3 and WS2/SiO2/Si structures. We prepared WS2 films with gradient thickness by annealing thickness-controlled WO3 films at 800 °C in sulfur atmosphere. Raman spectroscopy measurements showed step-like variation in the thickness of WS2 over substrates several centimeters in dimension. On fresh surfaces, we observed a significant change in the water contact angle depending on film thickness and substrate. Transmission electron microscopy analysis showed that differences in the surface roughness of WS2 films can account for the contrasting wetting properties between WS2/Al2O3 and WS2/SiO2/Si. The thickness dependence of water contact angle persisted for longer than 2 weeks, which demonstrates the stability of these wetting properties when exposed to air contamination.

A Paleoparasitological Study on the Capital Area of the Ancient Korean Kingdom.

A paleoparasitological study was performed on soil samples obtained at archaeological sites dating to the Baekje period in ancient Korean history. The samples were obtained from Buyeo, the capital area of the Baekje Kingdom, and from others corresponding to provincial counties of the same period. We found Ascaris lumbricoides and Trichuris trichiura eggs in the Buyeo samples but not any in the samples from the provincial counties. Our results suggest that the parasite-egg contamination patterns were closely correlated with population densities, in that the provincial counties of the Kingdom, compared with the capital Buyeo, were very sparsely populated. This is the first comprehensive paleoparasitological report on soil contamination patterns in the capital of the Baekje Kingdom, one of the most highly populated areas in ancient Korean history.

Lower extremity muscle activation and function in progressive task-oriented training on the supplementary tilt table during stepping-like movements in patients with acute stroke hemiparesis.

An effective and standardized method for applying a tilt table as a supplementary treatment in the early rehabilitation of stroke patients is still missing. The aim of this study was to determine the influence of progressive task-oriented training on the tilt table on the improvement in lower extremity (LE) muscle activation and clinical function in subjects with hemiplegia due to stroke. Thirty-nine subjects with acute stroke were randomly allocated to three groups; control group, tilt table group, and task-oriented training group on the tilt table, with 13 patients, respectively. All of the subjects received the routine therapy for half an hour, and subjects in the experimental groups additionally received training on two different tilt table applications for 20min a day, five times a week for three weeks. The effect of tilt table applications was assessed using the surface electromyography (EMG) analysis during stepping-like movements on the tilt table for LE muscle activation and clinical scores for function. Our results showed that there was a significantly greater increase in the EMG patterns of the extensors and flexors of the affected leg muscles during flexion and extension movements of both legs and clinical scores in patients undergoing the progressive task-oriented training on the tilt table compared to the other groups. These findings suggest that progressive task-oriented training on the tilt table can improve LE muscle activation and clinical scores of functional performance for early rehabilitation of subjects with acute stroke.

A case of congenital hypertrophic cardiomyopathy.

Congenital hypertrophic cardiomyopathy (HCMP) is a very rare congenital heart disease. Here, we report a case of neonatal HCMP, which was confirmed by two-dimensional echocardiography and autopsy. The HCMP rapidly progressed and the patient's condition deteriorated, despite the treatment for congestive heart failure.