Physics and Astronomy

Proffesor

Koyama, Keiichi

Magnetism and Magneto-Science: high magnetic field effect in materials science

Change of the equilibrium state of ferromagnetic MnBi with high magnetic fields

Differential thermal analysis was carried out on ferromagnetic material MnBi at a temperature range of 300–773K in magnetic fields up to 45T to investigate the effect of high magnetic fields on the decomposition process and corresponding phase diagram. The decomposition temperature Tt (MnBi → Mn1.08 Bi + liquid Bi) increases from 632 K (at a zero field) to 714 K by applying a magnetic field of 45 T. Furthermore, the magnetocaloric effect of MnBi is observed in 11.5–45 T is in the vicinity of 689 K, showing that a field-induced composition process occurs. The obtained results show that the equilibrium state of MnBi can be controlled by using a high magnetic field. (Journal of Alloys and Compounds 509 (2011) L78-L80)

World-class High field quenching furnace developed by our lab. (20T-Superconducting magnet at Tohoku Univ.)

Magnetic-field-induced enhancement for synthesizing ferromagnetic MnBi phase by solid-state reaction sintering

Examination of equipment developed by under graduate students

Ferromagnetic MnBi was synthesized using a solid-state reaction sintering method in high magnetic fields up to 15 T. The fraction of ferromagnetic MnBi phase in the sample sintered at 15 T was about 70% by weight, which was much larger than that sintered in a zero magnetic field. It was found that high magnetic fields dramatically enhanced the formation of MnBi phase from bismuth and manganese. In addition, the c-axis of a hexagonal structure of MnBi was oriented parallel to the magnetic field direction. These magnetic field effects on the synthesizing process were examined based on the gain of the Zeeman energy and the uniaxial magnetic anisotropy of MnBi phase. (Journal of Alloys and Compounds 615 (2014) 131-134)

Profile

Physics and Astronomy

Proffesor

Koyama, Keiichi

1997-1998:Postdoc, Institute for Solid State Physics, University of Tokyo, Japan
1998-2001:Research Associate, Institute for Materials Research, Tohoku University, Japan
2001-2009:Associate Professor, Institute for Materials Research, Tohoku University, Japan
2010-present:Professor, Graduate School of Science and Engineering, Kagoshima University, Japan

Message for Students

This laboratory was established in January 2010 at Kagoshima University in order to study basic magnetism and magnetoscience. The instruments in the laboratory are superconducting magnets, differential scanning calorimetry, differential thermal analysis under high magnetic fields, high pressure equipments, extraction-type magnetometer, vibrating sample magnetometer, arc-furnace, heat treatment system subject to high magnetic field, quenching furnace subject to high magnetic fields, etc. Two doctoral course students, six masters course students and four undergraduate students study in this laboratory.

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