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Journal Articles

Magnetocaloric effect of Sr-substituted BaFeO$$_{3}$$ in the liquid nitrogen and natural gas temperature regions

Yoshii, Kenji; Hayashi, Naoaki*; Mizumaki, Masaichiro*; Takano, Mikio*

AIP Advances (Internet), 7(4), p.045117_1 - 045117_6, 2017/04

 Times Cited Count:6 Percentile:40.28(Nanoscience & Nanotechnology)

We have investigated the magnetocaloric effect (MCE) of Ba$$_{1-x}$$Sr$$_{x}$$Fe$$^{4+}$$O$$_{3}$$ (x$$underline{<}$$0.2), a series of cubic perovskites showing a field-induced transition from helical antiferromagnetism to ferromagnetism. The maximum magnetic entropy change (-$$Delta$$S$$_{max}$$) at 50 kOe varies from $$sim$$ 5.8 J kg$$^{-1}$$K$$^{-1}$$ (x=0) to $$sim$$ 4.9 J kg$$^{-1}$$K$$^{-1}$$ (x=0.2), while the refrigerant capacity remains almost the same at $$sim$$165 J kg$$^{-1}$$. Interestingly, the temperature of -$$Delta$$S$$_{max}$$ decreases from $$sim$$116 K to $$sim$$77 K with increasing x, providing this series of rare-earth-free oxides with potential as a magnetic refrigerant for the liquefaction of nitrogen and natural gas.

Journal Articles

Electronic structure of BaFeO$$_{3}$$ studied by X-ray spectroscopy

Mizumaki, Masaichiro*; Fujii, Hitoshi*; Yoshii, Kenji; Hayashi, Naoaki*; Saito, Takashi*; Shimakawa, Yuichi*; Uozumi, Takayuki*; Takano, Mikio*

Physica Status Solidi (C), 12(6), p.818 - 821, 2015/06

 Times Cited Count:8 Percentile:94.79

We investigated the electronic structure of BaFeO$$_{3}$$ by using HAXPES and XAS measurements and first principle studies. The experimental and theoretical results indicated that BaFeO$$_{3}$$ is a negative charge transfer compound. We concluded that the on-site Coulomb energy and the strong hybridization between Fe-3d and O-2p orbitals play a very important role of emergence of negative charge transfer. And we found the new structure in the Fe-2p XPS spectrum and concluded this structure is originated from non-local screening.

Journal Articles

Suppression of temperature hysteresis in negative thermal expansion compound BiNi$$_{1-x}$$Fe$$_{x}$$O$$_{3}$$ and zero-thermal expansion composite

Nabetani, Koichiro*; Muramatsu, Yuya*; Oka, Kengo*; Nakano, Kiho*; Hojo, Hajime*; Mizumaki, Masaichiro*; Agui, Akane; Higo, Yuji*; Hayashi, Naoaki*; Takano, Mikio*; et al.

Applied Physics Letters, 106(6), p.061912_1 - 061912_5, 2015/02

 Times Cited Count:48 Percentile:89.86(Physics, Applied)

Negative thermal expansion (NTE) of BiNi$$_{1_x}$$Fe$$_x$$O$$_3$$ is investigated by dilatometric curves, synchrotron X-ray diffraction, and X-ray absorption spectroscopy. All samples (x=0.05-0.15) shows large NTE with the coefficient of linear thermal expansion which induced by charge transfer between Bi$$^{5+}$$ and Ni$$^{2+}$$ in the controlled temperature range near room temperature. Compared with Bi$$_{1_x}$$Ln$$_x$$NiO$$_3$$ (Ln: rare-earth elements), the thermal hysteresis that causes a problem for practical application is suppressed because random distribution of Fe in the Ni site changes the first order transition to second order-like transition.

Journal Articles

Orbital magnetic moment and coercivity of SiO$$_2$$-coated FePt nanoparticles studied by X-ray magnetic circular dichroism

Takahashi, Yukio*; Kadono, Toshiharu*; Yamamoto, Shimpei*; Singh, V. R.*; Verma, V.*; Ishigami, Keisuke*; Shibata, Goro*; Harano, Takayuki*; Takeda, Yukiharu; Okane, Tetsuo; et al.

Physical Review B, 90(2), p.024423_1 - 024423_5, 2014/07


 Times Cited Count:5 Percentile:27.7(Materials Science, Multidisciplinary)

Journal Articles

Magnetocaloric effect of field-induced ferromagnet BaFeO$$_{3}$$

Mizumaki, Masaichiro*; Yoshii, Kenji; Hayashi, Naoaki*; Saito, Takashi*; Shimakawa, Yuichi*; Takano, Mikio*

Journal of Applied Physics, 114(7), p.073901_1 - 073901_6, 2013/08

 Times Cited Count:19 Percentile:67.04(Physics, Applied)

We have investigated the magnetocaloric effect (MCE) of a perovskite oxide, BaFeO$$_{3}$$, that shows ferromagnetism by the aid of a small external field of about 0.3 T below the Curie temperature T$$_{C}$$ = 111 K. The magnetization is found to change almost reversibly in both field and temperature cycles. Hence, magnetic and thermal hysteretic losses are negligibly low during refrigeration, a property that is suitable for application. The reversible MCE is likely to arise from the absence of an orbital magnetic moment of Fe ions which are essentially in the Fe$$^{3+}$$L state (L: ligand hole). The magnetic entropy change and refrigerant capacity near the T$$_{C}$$ are about 5.8 J kg$$^{-1}$$ K$$^{-1}$$ and about 172 J kg$$^{-1}$$, respectively, both of which are comparable to those of ferromagnetic perovskite manganites. As BaFeO$$_{3}$$ contains no rare metals and is stable against corrosion, the material can be regarded as a candidate refrigerant material.

Journal Articles

Quasiparticle interference and superconducting gap in Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$

Hanaguri, Tetsuo*; Kosaka, Yuki*; Davis, J. C.*; Lupien, C.*; Yamada, Ikuya*; Azuma, Masaki*; Takano, Mikio*; Oishi, Kazuki; Ono, Masaki*; Takagi, Hidenori*

Nature Physics, 3(12), p.865 - 871, 2007/12

 Times Cited Count:134 Percentile:95.94(Physics, Multidisciplinary)

Journal Articles

Soft X-ray magnetic circular dichroism study of Ca$$_{1-x}$$Sr$$_x$$RuO$$_3$$ across the ferromagnetic quantum phase transition

Okamoto, Jun*; Okane, Tetsuo; Saito, Yuji; Terai, Kota*; Fujimori, Shinichi; Muramatsu, Yasuji*; Yoshii, Kenji; Mamiya, Kazutoshi*; Koide, Tsuneharu*; Fujimori, Atsushi; et al.

Physical Review B, 76(18), p.184441_1 - 184441_5, 2007/11

 Times Cited Count:26 Percentile:72.38(Materials Science, Multidisciplinary)

Ca$$_{1-x}$$Sr$$_x$$RuO$$_3$$, which is ferromagnetic for Sr concentration x $$>$$ 0.3, has been studied by X-ray magnetic circular dichroism (XMCD) in Ru 3$$p$$ and O 1$$s$$ core-level X-ray absorption. XMCD signals appear at x $$sim$$ 0.3 and monotonically increases with x in the ferromagnetic phase. While the monotonic increase of the XMCD signals with x is of a typical Stoner-type, the absence of appreciable change in the spectral line shapes of both the Ru 3$$p$$ and O 1$$s$$ XMCD spectra indicate that the itinerant-electron ferromagnetism in Ca$$_{1-x}$$Sr$$_x$$RuO$$_3$$ is influenced by strong electron correlation.

Journal Articles

Low-energy spectroscopic mapping studies in optimally-doped Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$

Hanaguri, Tetsuo*; Kosaka, Yuki*; Davis, J. C.*; Lupien, C.*; Yamada, Ikuya*; Azuma, Masaki*; Takano, Mikio*; Oishi, Kazuki; Takagi, Hidenori*

Physica C, 460-462, p.954 - 955, 2007/09

 Times Cited Count:1 Percentile:7.1(Physics, Applied)

We performed high-resolution scanning tunneling microscopy/spectroscopy on an optimally-doped Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$ crystal. The so-called checkerboard local-density-of-state modulation manifests in the spectroscopic map of the optimally-doped sample. In addition, spatially-inhomogeneous energy gap is observed. The gap tends to be buried at elevated temperatures and correlates with the checkerboard modulation. These results suggest that the gap is related to superconductivity which coexists with the checkerboard modulation.

Journal Articles

Characterization of electrode/electrolyte interface for lithium batteries using ${it in situ}$ synchrotron X-ray reflectometry; A New experimental technique for LiCoO$$_{2}$$ model electrode

Hirayama, Masaaki*; Sonoyama, Noriyuki*; Abe, Takashi*; Minoura, Machiko*; Ito, Masumi*; Mori, Daisuke*; Yamada, Atsuo*; Kanno, Ryoji*; Terashima, Takahito*; Takano, Mikio*; et al.

Journal of Power Sources, 168(2), p.493 - 500, 2007/06

 Times Cited Count:80 Percentile:90.21(Chemistry, Physical)

A new experimental technique was developed for detecting structure changes at electrode/electrolyte interface of lithium cell using X-ray reflectometry and two-dimensional model electrodes with a restricted lattice-plane. The electrodes were constructed with an epitaxial film of LiCoO$$_{2}$$ synthesized by pulsed laser deposition method. The anisotropic properties were confirmed by electrochemical measurements. ${it Ex situ}$ X-ray reflectivity measurements indicated that the impurity layer existed on the as-grown LiCoO$$_{2}$$ was dissolved and a new SEI layer with lower density was formed after soaking into the electrolyte. ${it In situ}$ X-ray reflectivity measurements indicated that the surface roughness of the intercalation (1 1 0) plane increased with applying voltages, while no significant changes in surface morphology were observed for the intercalation non-active (0 0 3) plane during the pristine stage of the charge-discharge process.

Journal Articles

Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO$$_3$$

Belik, A. A.*; Iikubo, Satoshi; Yokosawa, Tadahiro*; Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Azuma, Masaki*; Takano, Mikio*; Kimoto, Koji*; Matsui, Yoshio*; et al.

Journal of the American Chemical Society, 129(4), p.971 - 977, 2007/01

 Times Cited Count:167 Percentile:95.31(Chemistry, Multidisciplinary)

Structural properties of polycrystalline single-phased BiMnO$$_3$$ samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO$$_3$$ crystallizes in the centrosymmetric space group C2/c at 300 K. The analysis of Mn-O bond lengths suggested that the orbital order present in BiMnO$$_3$$ at 300 K melts above T= 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature.

Journal Articles

Neutron powder diffraction study on the crystal and magnetic structures of BiCoO$$_3$$

Belik, A. A.*; Iikubo, Satoshi; Kodama, Katsuaki; Igawa, Naoki; Shamoto, Shinichi; Niitaka, Seiji*; Azuma, Masaki*; Shimakawa, Yuichi*; Takano, Mikio*; Izumi, Fujio*; et al.

Chemistry of Materials, 18(3), p.798 - 803, 2006/02

 Times Cited Count:241 Percentile:98.55(Chemistry, Physical)

The crystal and magnetic structures of polycrystalline BiCoO$$_3$$ have been determined by the Rietveldmethod from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO$$_3$$ (space groupP4mm; Z=1; a=3.72937(7) ${AA}$ and c=4.72382(15) ${AA}$ at room temperature; tetragonality c/a=1.267) is isotypic with BaTiO$$_3$$ and PbTiO$$_3$$ in the whole temperature range. BiCoO$$_3$$ is an insulator with a Neeltemperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagationvector of k=(1/2, 1/2, 0). In this model, magnetic moments of Co$$^{3+}$$ ions are parallel to the c directionand align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagneticallyalong the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300K are 3.24(2)$$mu$$$$_B$$ and 2.93(2)$$mu$$$$_B$$, respectively. The structure refinements revealed no deviation fromstoichiometry in BiCoO$$_3$$. BiCoO$$_3$$ decomposed in air above 720 K to give Co$$_3$$O$$_4$$ and sillenite-like Bi$$_{25}$$CoO$$_{39}$$.

Journal Articles

Magnetic excitations from the linear Heisenberg antiferromagnetic spin trimer system A$$_3$$Cu$$_3$$(PO$$_4$$)$$_4$$ (A=Ca, Sr, and Pb)

Matsuda, Masaaki; Kakurai, Kazuhisa; Belik, A. A.*; Azuma, Masaki*; Takano, Mikio*; Fujita, Masaki*

Physical Review B, 71(14), p.144411_1 - 144411_5, 2005/04

 Times Cited Count:29 Percentile:73.55(Materials Science, Multidisciplinary)

Inelastic neutron scattering experiments were performed on A$$_3$$Cu$$_3$$(PO$$_4$$)$$_4$$ (A=Ca, Sr, and Pb), which consists of one-dimensional array of linear copper spin trimers. It was found that the magnetic excitations are well described by the linear Heisenberg antiferromagnetic spin trimer model without adjustable parameters except the overall scale factor. The intra-trimer coupling contants are determined to be 9.39(4), 9.99(4), and 9.07(4) meV for A$$_3$$Cu$$_3$$(PO$$_4$$)$$_4$$ with A=Ca, Sr, and Pb, respectively.

Journal Articles

Antiferromagnetic-to-ferromagnetic transition induced by diluted Co in SrFe$$_{1-x}$$Co$$_x$$O$$_3$$:Magnetic circular X-ray dichroism study

Okamoto, Jun*; Mamiya, Kazutoshi*; Fujimori, Shinichi; Okane, Tetsuo; Saito, Yuji; Muramatsu, Yasuji*; Yoshii, Kenji; Fujimori, Atsushi*; Tanaka, Arata*; Abbate, M.*; et al.

Physical Review B, 71(10), p.104401_1 - 104401_5, 2005/03

 Times Cited Count:20 Percentile:63.69(Materials Science, Multidisciplinary)

The antiferromagnetic-to-ferromagnetic transition in SrFe$$_{1-x}$$Co$$_x$$O$$_3$$ ($$x_c$$$$simeq$$0.15) induced by Co doping has been studied by magnetic circular X-ray dichroism. The orbital and spin magnetic moments of the Fe and Co 3$$d$$ states under the magenetic field of 2 T are found to show different $$x$$ dependences: The spin polarization of Fe 3$$d$$ gradually increases with Co concentration; On the other hand, a large spin polarization of Co 3$$d$$ is induced already in the antiferromagnetic phase, indicating that the Co moment is nearly fully alligned already in the antiferromagnetic phase. This suggests that the alignment of the Fe magnetic moment in SrFe$$_{1-x}$$Co$$_x$$O$$_3$$ is induced by interaction with doped Co magnetic moment. Possible formation of ferromagnetic Co rich region is discussed.

Journal Articles

Study of Photo-Cathode RF Gun for a High Brightness Electron Beam

Yamazaki, Yoshio; Hirano, Koichiro*; Fukuda, Satoshi*; Takano, Mikio*; Araki, Sakae*; Terunuma, Nobuhiro*; Urakawa, Junji*

Proceedings of 9th European Particle Accelerator Conference (EPAC 2004), 0 Pages, 2004/07

Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.

Journal Articles

Charge-ordered state in single-crystalline CaFeO$$_{3}$$ thin film studied by X-ray anomalous diffraction

Akao, Tadahiro*; Azuma, Yusuke; Usuda, Manabu; Nishihata, Yasuo; Mizuki, Junichiro; Hamada, Noriaki*; Hayashi, Naoaki*; Terashima, Takahito*; Takano, Mikio*

Physical Review Letters, 91(15), p.156405_1 - 156405_4, 2003/10

 Times Cited Count:31 Percentile:79.13(Physics, Multidisciplinary)

X-ray anomalous diffraction, together with a band structure calculation, was employed to obtain a quantitative comprehension of the charge-ordering state in a single-crystalline CaFeO$$_{3}$$ thin film. The experimental results show a characteristic energy dispersion of the near inhibited reflection at 150, implying Fe atoms split into two distinct states. The energy dispersion is in good agreement with the calculated spectrum based on LDA+U scheme. The calculation reveals an electronic configuration of the Fe 3d orbital follows a localization in the oxygen orbital surrounds one of the distinct Fe atoms.

Journal Articles

Synthesis of materials under high pressure by means of synchrotron X-ray diffraction

Azuma, Masaki*; Saito, Takashi*; Niitaka, Seiji*; Ishiwata, Shintaro*; Kanda, Hiroaki*; Yamada, Ikuya*; Takano, Mikio*; Utsumi, Wataru

Kotai Butsuri, 38(2), p.141 - 150, 2003/02

no abstracts in English

Journal Articles

Single-crystal growth of transition metal oxides at high pressures of several GPa

Azuma, Masaki*; Saito, Takashi*; Ishiwata, Shintaro*; Yoshida, Hirofumi*; Takano, Mikio*; Kosaka, Yuki*; Takagi, Hidenori*; Utsumi, Wataru

Journal of Physics; Condensed Matter, 14(44), p.11321 - 11324, 2002/11

 Times Cited Count:7 Percentile:39.68(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Single crystal growth of the high pressure phase of (VO)$$_{2}$$P$$_{2}$$O$$_{7}$$ at 3GPa

Saito, Takashi*; Terashima, Takashi*; Azuma, Masaki*; Takano, Mikio*; Goto, Tadashi*; Ota, Hiroshi*; Utsumi, Wataru; Bordet, P.*; Johnston, D. C.*

Journal of Solid State Chemistry, 153(1), p.124 - 131, 2000/08

 Times Cited Count:35 Percentile:79.22(Chemistry, Inorganic & Nuclear)

no abstracts in English

Journal Articles

Magnetic properties and single crystal growth of a spin gapped compound, high pressure phase of (VO)$$_{2}$$P$$_{2}$$O$$_{7}$$

Saito, Takashi*; Azuma, Masaki*; Takano, Mikio*; Hiroi, Zenji*; Narumi, Yasuo*; Kindo, Koichi*; Utsumi, Wataru

Funtai Oyobi Fummatsu Yakin, 46(9), p.1014 - 1019, 1999/09

no abstracts in English

Journal Articles

Neutron-diffraction study of Na- and K-jarosites

Inami, Toshiya*; Maegawa, S.*; Takano, Mikio*

J. Magn. Magn. Mater., 177-181, p.752 - 753, 1998/00

 Times Cited Count:18 Percentile:67.38(Materials Science, Multidisciplinary)

no abstracts in English

25 (Records 1-20 displayed on this page)