Makoto Ohtani

Fabrication of spin-frustrated Sm2Mo2O7 epitaxial films: High throughput optimization using a temperature gradient method

Epitaxial thin films of pyrochlore-type ferromagnetic molybdates Sm2Mo2O7, as a geometrically spin-frustrated system, were fabricated by a pulsed-laser deposition. The temperature gradient method combined with the concurrent x-ray diffraction method was exploited for high throughput optimization of the film quality. The excess supply of Mo for compensating the volatile Mo-related species improved the crystallinity. The resistivity and magnetization of the optimized film were 3 mΩu200acm and 0.8u2009μB/Mo at 10 K, respectively, being similar to those of a single crystal. The observed finite anomalous Hall term that persists down to the lowest temperature reflects an appearance of spin chirality in this spin-frustrated system.

High throughput oxide lattice engineering by parallel laser molecular-beam epitaxy and concurrent x-ray diffraction

A laser molecular-beam epitaxy (LMBE) system for the fabrication of atomically controlled oxides superlattices and an x-ray diffractometer that measures spatially resolved x-ray diffraction spectra have been developed based on the concept of combinatorial methodology. The LMBE chamber has two moving masks, an automated target stage, a substrate heating laser, and an in situ scanning reflection high-energy electron diffraction system. The x-ray diffractometer with a curved monochromator and two-dimensional detector is used for rapid concurrent x-ray diffraction intensity mapping with the two axes of the detector corresponding to the diffraction angle and a position in the sample.

Synthesis and characterization of composition-spread (Sr,Ca)2CuO3 thin films with high third-order optical nonlinearity

The optical properties of composition-spread (SrxCa1−x)2CuO3(0⩽x⩽1) films showing high third-order optical nonlinearity are systematically investigated. Desired orientations and high crystallinity are obtained for the entire composition x by employing a composition-spread [(Sr2TiO4)x(LaSrAlO4)1−x] buffer layer and a temperature-gradient method in order to compensate the change in lattice mismatch and growth temperature depending on x. Linear absorption spectra and third-harmonic intensity with an exciting wavelength of 1.56 μm are measured as a function of x. As the Cu–O bond length increases with x, the charge-transfer gap decreases and the third-harmonic intensity increases, and both the charge-transfer gap and third-harmonic intensity change almost linearly with x between Ca2CuO3 and Sr2CuO3.

High-throughput characterization of linear and nonlinear optical properties in composition-spread (Sr,Ca)2CuO3 thin-films

Abstract We have constructed a high-throughput spectrometer and a nonlinear optical tester used for the characterization of combinatorial thin-film libraries. The optical spectrometer consists of a multi-channel detector and an automated bidimensional translation stage. The transmission spectrum of an area of 0.5 mm ×2 xa0mm can be measured for a wavelength range of 280–900xa0nm. Our nonlinear optical tester uses a compact mode-locked fiber-laser as an excitation source. The laser beam is focused by a graded index lens, the fundamental light is filtered out, and the third-harmonic (TH) light is detected by a photomultiplier. The data collection and the motion of the stepping motor-driven stage are synchronized. Typical measurement time for a composition-spread thin-film is 5xa0min. A demonstration is shown for a composition-spread thin-film of one-dimensional cuprate (SrxCa1−x)2CuO3 with gigantic third-order optical nonlinearity.

Observation of Compositional Fluctuation by Scanning Superconducting Quantum Interference Device (SQUID) Microscope in Superconducting La1.8Sr0.2CuO4

In order to visualize spatial distributions of vortices strongly pinned in La1.8Sr0.2CuO4, we have performed scanning superconducting quantum interference device (SQUID) microscopic (SSM) measurements near Tc. The obtained SSM images have revealed that stripe-shaped regions with higher Tc run in an arbitrary direction with respect to crystallographic axes. Vortices tend to align in a one-dimensional fashion, negotiating around the higher Tc regions. High-resolution electron probe micro-analysis confirmed that the spatial variation in Tc corresponds well to the modulation of Sr/La composition. We also found that small-angle grain boundaries with tilt angles of 1–3 degrees are less effective in trapping vortices, indicating that superconductivity is not degraded very much.

Quick optimization of Y-type magnetoplumbite thin films growth by combinatorial pulsed laser deposition technique

Abstract Quick growth optimization of complex oxide, Y-type magnetoplumbite (Ba 2 Co 2 Fe 12 O 22 (Co 2 Y)) thin films is demonstrated by using combinatorial thin film technology. Planning a CoO buffer layer on MgAl 2 O 4 (1xa01xa01) substrate was found to be very effective for preventing the phase separation of Co deficient impurity (BaFe 2 O 4 ) and forming the desired Co 2 Y phase. The combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction facilitate the production of Y-type magnetoplumbite thin film in a single phase.