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Yokohama-shi, Japan

Mizusaki S.,Aoyama Gakuin University | Douzono A.,Aoyama Gakuin University | Ohnishi T.,Aoyama Gakuin University | Ozawa T.C.,Japan International Center for Materials Nanoarchitectonics | And 2 more authors.
Journal of Alloys and Compounds | Year: 2013

We report the composition-induced metal-insulator crossover transition in Ti substituted Ru-based metallic full Heusler alloy Ru2MnGe where the both end of materials shows a metallic properties. The samples at the middle composition show the large negative magnetoresistance effect. The experimental results of the resistivity and the magnetization indicate that this metal-insulator transition is induced by the Kondo effect because Ti atoms on antiferromagnetic Ru2MnGe have an important role in appearance of insulator states. © 2012 Elsevier B.V. All rights reserved. Source


Mizusaki S.,Aoyama Gakuin University | Douzono A.,Aoyama Gakuin University | Ohnishi T.,Aoyama Gakuin University | Ozawa T.C.,Japan International Center for Materials Nanoarchitectonics | And 3 more authors.
Journal of Alloys and Compounds | Year: 2012

The present study reveals that the correlation between the magnetic properties with composition x in the polycrystalline Ru2Mn 1-xFexGe system. Hard ferromagnetic properties appeared at the intermediate composition between antiferromagnetic Ru2MnGe with soft ferromagnetic Ru2FeGe. Ru2Mn0.6Fe 0.4Ge shows an anisotropic and negative magnetoresistance (MR) effect more than 8% although the both end materials are small MR effect less than 1%. These experimental results correlate the variation in MR ratio with that of coercive field as a function of x. Moreover, the correlation is shown at the boundary of magnetism between antiferromagnetic and ferromagnetic. Therefore, the present experimental results imply that the coexistence of antiferromagnetic and soft ferromagnetic leads to induce the MR effect in this system. © 2011 Elsevier B.V. All rights reserved. Source


Ohnishi T.,Aoyama Gakuin University | Naito M.,Aoyama Gakuin University | Mizusaki S.,Aoyama Gakuin University | Nagata Y.,Aoyama Gakuin University | Noro Y.,Kawazoe Frontier Technologies Co.
Journal of Electronic Materials | Year: 2011

The magnetic, transport, and thermoelectric properties of Ca 1-x Sr x Ru 1-y Mn y O 3 have been investigated. Ferromagnetism with relatively high T C (>200 K) was introduced by Mn doping. In particular, ferromagnetism appeared in the Ca 0.5Sr 0.5Ru 1-y Mn y O 3 system at y > 0.2. The maximum T C (=270 K) was recorded for a specimen of Ca 0.5Sr 0.5Ru 0.4Mn 0.6O 3. The ferromagnetism seems to be due to the mixed-valence states of Mn 3+, Mn 4+, Ru 4+, and Ru 5+ ions. The metallic character of Ru-rich specimens was suppressed by Mn substitution, and the system was transformed into a semiconductor at relatively low Mn content near y = 0.1. Specimens with higher Mn content (y > 0.8) had large thermoelectric power (50 μV K -1 to 130 μV K -1 at 280 K) accompanied by relatively low resistivity (0.03 Ω cm to 1 Ω cm). The Ca 0.5Sr 0.5Ru 1-y Mn y O 3 system seems to have good potential as a thermoelectric material for use above 300 K. © 2010 TMS. Source


Mizusaki S.,Aoyama Gakuin University | Ohnishi T.,Aoyama Gakuin University | Douzono A.,Aoyama Gakuin University | Hirose M.,Aoyama Gakuin University | And 6 more authors.
Journal of Physics Condensed Matter | Year: 2012

The antiferromagnetism in Ru 2MnGe can be suppressed by the substitution of V by Mn and ferromagnetism appears. Synchrotron-based magnetic Compton scattering experiments are used in order to investigates the role of 3d electrons in the indirect/direct exchange interactions for the appearance of ferromagnetism. A small spin moment for the itinerant electron part on the magnetic Compton profile indicates that the metallic ferromagnet Ru 2Mn 0.5V 0.5Ge has a weak indirect exchange interaction between the d-like and sp-like (itinerant) electrons. This suggests that the appearance of ferromagnetism is caused by the enhancement of the direct exchange interactions between dd electrons in the Ru 2MnGe Heusler compound. These findings indicate that the indirect exchange interaction between itinerant electrons and localized electrons is a significant key point for the appearance of ferromagnetism in this system. © 2012 IOP Publishing Ltd. Source


Mizusaki S.,Aoyama Gakuin University | Ohnishi T.,Aoyama Gakuin University | Ozawa T.C.,Japan National Institute of Materials Science | Noro Y.,Kawazoe Frontier Technologies Co. | And 4 more authors.
IEEE Transactions on Magnetics | Year: 2011

The magnetic properties of the polycrystalline Heusler compound Co 2TiAl were investigated by the classical experimental methods and the magnetic Compton scattering experiment. The X-ray diffraction profile at room temperature can be identified as the phase of the L21-type ordered structure. The magnetic field and temperature dependence of magnetization show that Co2TiAl has the typical soft ferromagnetic properties with TC of 120 K and the saturation magnetization of 0.70 μB per formula unit. The resistivity shows a typical metallic behavior at temperatures up to 300 K. The magnetoresistance (MR) effect with the MR ratio of - 8% appears in the vicinity of TC. The characteristics of the magnetic Compton profile are similar to that of the well-known ferromagnetic metals such as Ni and Fe. The experimental results indicate that the origin of the MR effect observed for Co2TiAl is similar to that for conventional ferromagnetic materials. © 2011 IEEE. Source

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