Aoyama Gakuin University

About: Aoyama Gakuin University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 3494 authors who have published 6419 publications receiving 115648 citations. The organization is also known as: Aoyama gakuin daigaku.

Mechanism of carrier-induced ferromagnetism in magnetic semiconductors

Abstract: Taking into account both random impurity distribution and thermal fluctuations of localized spins, we have performed a model calculation for the carrier (hole) state in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ by using the dynamical coherent potential approximation. The result reveals that carriers are nearly bound to magnetic impurity sites and that the carrier spin strongly couples to the localized d spins on Mn ions. The hopping of carriers among Mn sites causes the ferromagnetic ordering of the localized spins through the double-exchange mechanism. The Curie temperature obtained by using conventional parameters agrees well with the experimental result for ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}.$

Performance of the helium dewar and the cryocoolers of the Hitomi soft x-ray spectrometer

Abstract: The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a He4 Joule–Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers.

Spin nematic order in multiple-spin exchange models on the triangular lattice.

Abstract: We figure out that the ground state of a multiple-spin exchange model applicable to thin films of solid $^{3}\mathrm{He}$ possesses an octahedral spin nematic order. In the presence of a magnetic field, it is deformed into an antiferroquadrupolar order in the perpendicular spin plane, in which lattice ${Z}_{3}$ rotational symmetry is also broken. Furthermore, this system shows a narrow magnetization plateau at half, $m/{m}_{\mathrm{sat}}=1/2$, which resembles recent magnetization measurements [H. Nema et al., Phys. Rev. Lett. 102, 075301 (2009)].