Hiroki Wadati

<jats:p>The crystal structure of La4Ge3S12 has been known to be noncentrosymmetric for almost four decades. This characteristic inversion symmetry breaking suggests the presence of nonlinear optical (NLO) properties. Yet, experimental observations of such phenomena, including second harmonic generation (SHG) have been reported only in recent studies. In this study, we synthesized La4Ge3S12 using the one‐step melting method, which is more straightforward than the conventional two‐step growth method. We characterized the composition, crystal structure, and electronic structure using electron probe microanalysis, powder X‐ray diffraction, and X‐ray photoelectron spectroscopy. The experimental electronic structure is in line with those obtained using first‐principle calculations. In addition, we observed the NLO properties of La4Ge3S12 in response to the ultrashort pulsed infrared laser. We found that the intensity of the SHG quadratically depends on the intensity of the incident light, mirroring the intrinsic nature of NLO.</jats:p>

Rocksalt-type heavy rare earth monoxides REOs (RE = Tb, Dy, Er) were synthesized as single phase epitaxial thin films for the first time. They exhibited metallic electronic states and a much higher T_C than the corresponding rare earth nitrides.

Abstract In the present study, we investigated the magnetization dynamics of a Gd₂₃Fe₆₇Co₁₀ nanofilm. We subjected the nanofilm to a time-resolved experiment to examine its magneto-optical effect using an X-ray free electron laser. By tuning the energy of the photons to the core-level resonance of the Fe absorption edge, we selectively determined the magnetic behavior of the elements at the Fe site in the nanofilm. When triggered by an ultrashort pulse of infrared radiation, the materials underwent demagnetization and magnetic reversal, depending on fluence of the laser. The following relaxation process was found to be associated not only with the fast recursion but also with a long sustention of the reversed magnetization. The experimental observation consistently match with the recent prediction by the magnetic dynamic simulation. The ultrafast dynamics was triggered by the ultrafast thermal effect and it was recovered toward the initial state in the non-thermal manner.

Abstract In this study, we show that doping lanthanides into lamellar crystals reorganizes the lamellar structure and dramatically changes the crystal morphology. Azo-DA, a compound with azobenzene derivatives and carboxylic acids at both ends of the diacetylene moiety, formed plate-like lamellar crystals. The doping of holmium (Ho), a lanthanide, into the film obtained by stacking Azo-DA lamellar crystals, promoted a dramatic change in crystal morphology, resulting in the formation of an Azo-DA/Ho film with a radial lamellar crystal structure. A detailed investigation of the crystal growth process revealed that Azo-DA/Ho, which is slightly formed in the solution phase during Ho doping, acts as a pseudonucleating agent and dramatically changes the morphology of the lamellar crystals. Additionally, the morphological changes in the lamellar crystal films significantly changed the surface properties of the films, such as their appearance and water repellency. Similar morphological changes in lamellar crystals were induced when other lanthanide elements were used instead of Ho, and the type of lanthanide dopant can affect the magnetic properties of the films.

<p>Background: Magneto-optical Kerr effect (MOKE) microscopes are powerful experimental tools to observe magnetic domains in magnetic materials. These devices are, however, typically large, unportable, and expensive (∼ several million yen), and therefore prevent many researchers in the field of materials science from easy access to study real-space images of magnetic domains.</p><p>Methods: To overcome these issues, we utilize data from ”The OpenFlexure Project” developed by the University of Bath and the University of Cambridge. The purpose of this project is to make high-precision mechanical positioning of the studied sample available to anyone with a 3D printer, especially for use in microscopes. We built a low-cost and portable MOKE microscope device by a 3D printer. We redesigned the 3D modeling data of an ordinary optical microscope provided by The OpenFlexure project and incorporated additional elements such as optical polarizers and an electro-magnetic coil into the primarily designed microscope that did not originally have these</p><p> elements.</p><p>Results: We successfully observed magnetic domains and their real-space motions induced by magnetic fields using the palm-sized low-cost MOKE microscope, which costs approximately 20,000 yen in raw materials to construct.</p><p>Conclusions: Our methodology to assemble a low-cost MOKE microscope will enable researchers working in the field of materials science to more easily observe magnetic domains without commercial equipment.</p>

<jats:p> We studied the relationship between the lattice constant and magnetism of [Formula: see text]-ordered FePt under high pressure by means of first-principles calculations and synchrotron x-ray measurements. Based on our calculations, we found that the c/ a ratio shows a local maximum at ∼20 GPa and that the Pt magnetic moment first remains almost unchanged and is sharply suppressed at ∼60 GPa. As for the c/ a, we experimentally verified the local maximum at ∼20 GPa by powder x-ray diffraction. We also measured the x-ray magnetic circular dichroism at the Pt L edge up to ∼20 GPa. Any significant change in the Pt magnetic moment was not observed in agreement with the calculations. These results, thus, indicate that magnetic states, where the magnetization of Fe decreased and that of Pt did not change, can be created in [Formula: see text]-ordered FePt by lattice deformation under high pressure. </jats:p>

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu2ZnSnSe4 (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu2ZnSnSe4. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming CuZn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds.

<title>Abstract</title>Investigation of ultrafast dynamic behaviors can provide novel insights about the coupling mechanisms among multiple degrees of freedom in condensed matters, such as lattice, magnetism and electronic structure. Here we investigate both the ferromagnetic (FM) and antiferromagnetic (AFM) dynamics of a strongly correlated oxide system, GdBaCo₂O_5.5 thin film by time-resolved x-ray magnetic circular dichroism in reflectivity (XMCDR) and resonant magnetic x-ray diffraction (RMXD). A photo-induced AFM-FM transition characterized by an increase of the transient XMCDR (sensitive to FM order) beyond the unpumped value and a decay of RMXD (sensitive to AFM order) was observed. The photon-energy dependence of the transient XMCDR and reflectivity could be interpreted as a concomitant photo-induced spin-state transition (SST). The AFM-FM transition and SST couple with each other in the time domain, resulting in unusual dynamic behaviors of the magnetism.

The interface properties of strongly correlated electron system/band semiconductor junctions were investigated in the La_1−xSr_xVO₃/p-Si(100) structure. Spectroscopic observations show that the electronic structure of the interface is typical of insulator/semiconductor junctions for x ≤ 0.2 and Schottky junctions for x ≥ 0.25. For the forward current density–bias voltage (J–V) characteristics, energy barriers that were otherwise unexplainable by spectroscopy were estimated from the thermionic emission model fitting of the J–V characteristics, indicating that the injected carriers from Si to La_1−xSr_xVO₃ can also feel the correlation force of Coulomb repulsion at the interface.

Soft X-ray absorption study for low-crystallinity metal organic frameworks to investigate the ligand field.