Papers by Author: Atsushi Ashida

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Authors: Kazuhiro Maeda, Takeshi Yoshimura, Atsushi Ashida, Norifumi Fujimura
Abstract: Relationship between magnetic ordering and ferroelectric polarization switching in YMnO3 epitaxial thin film was investigated. It was found that Néel point of the YMnO3 film is below 80 K, which is consistent with that of YMnO3 single crystal by neutron diffraction. From temperature dependence of the polarization-electric field hysteresis loops and the dielectric permittivity-voltage characteristics, ferroelectric polarization switching behavior was investigated from 300 to 10 K in detail. The ferroelectric polarization switching behavior accords with Ishibashi-Orihara’s theory. Moreover, it was found that the dielectric permittivity under bias electric field have a anomaly below 80 K and the nucleation density for the ferroelectric polarization switching decreases below 130 K, which is higher than 80K.
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Authors: Keiichiro Masuko, Tatsuru Nakamura, Atsushi Ashida, Takeshi Yoshimura, Norifumi Fujimura
Abstract: The transport properties of Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructures (x≤0.15) were investigated. The heterostructures were fabricated on ZnO single-crystal substrates by a pulsed laser deposition system. Atomic force microscope observation and X-ray diffraction analysis suggested that Zn0.88-xMgxMn0.12O layers have atomically flat surface and excellent crystallinity. The results of Hall measurement for Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructure with x=0.075 revealed that the carrier concentration and the electron mobility were 5.1×1012cm-2 and 800 cm2/Vs at 10 K, respectively, suggesting that the carrier confinement effect exits at the heterointerface between Zn0.88-xMgxMn0.12O barrier layer and ZnO channel layer. In the magnetoresistance (MR) measurement at 1.85 K, a positive MR behavior was observed below 0.5 T, while a negative MR behavior was recognized above 0.5 T. The slope of the positive MR decreased with increasing the temperature and was well fitted to the Brillouin function with S=5/2. The electrical and magneto-transport properties were very similar to those of Zn0.88Mn0.12O/ZnO heterostructures without doping Mg.
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Authors: Takeshi Yoshimura, Kazuhiro Maeda, Atsushi Ashida, Norifumi Fujimura
Abstract: The switching behavior of the ferroelectric polarization of magnetoferroelectric YMnO3 epitaxial films at around the Néel temperature was investigated to discuss the effect of the antiferromagnetic ordering on the ferroelectric domain wall motion. From neutron diffractions to investigate the antiferromagnetic ordering and measurements of polarization-electric field, dielectric constant, and the time constant of the domain wall motion, the change of the domain wall motion is suggested at around 120 K, which is higher than the Néel temperature (~80 K).
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Authors: Atsushi Ashida, T. Nagata, Tadashi Ito
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Authors: M. Izaki, H. Ishizaki, Atsushi Ashida, T. Omi, Tadashi Ito
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