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Journal Articles

Perpendicular magnetic anisotropy of thin films

Takanashi, Koki; Seki, Takeshi*

Magune, 19(3), p.100 - 106, 2024/06

Perpendicular magnetic anisotropy of thin films currently plays an important role in spintronics as well as magnetic recording. Regarding perpendicular magnetic anisotropy, in this article, the fundamentals, the research history, and the recent research trends are reviewed, showing specific examples with perpendicular magnetization such as magnetic multilayers, ordered alloy films, rare earth-transition metal amorphous alloy films, and inhomogeneous or granular films. The physical origins for perpendicular magnetic anisotropy, including interface anisotropy due to structural symmetry breaking, magnetoelastic anisotropy due to strain, bulk-type magnetocrystalline anisotropy, and directional pair ordering of atoms, are discussed in each example.

Journal Articles

Incorporation of U, Pb and rare earth elements in calcite through crystallisation from amorphous calcium carbonate; Simple preparation of reference materials for microanalysis

Miyajima, Yusuke*; Saito, Ayaka*; Kagi, Hiroyuki*; Yokoyama, Tatsunori; Takahashi, Yoshio*; Hirata, Takafumi*

Geostandards and Geoanalytical Research, 45(1), p.189 - 205, 2021/03

https://doi.org/10.1111/ggr.12367

Times Cited Count：6 Percentile：33.39(Geochemistry & Geophysics)

Uncertainty for elemental and isotopic analyses of calcite by LA-ICP-MS is largely controlled by the homogeneity of the reference materials (RMs) used for normalization and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb, and rare earth elements into calcite through heat- and pressure-induced crystallization from amorphous calcium carbonate that was precipitated from element-doped reagent solution. X-ray absorption spectra showed that U was present as U(VI) in the synthesized calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison to synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The $^{207}$ Pb/ $^{206}$ Pb ratio in the calcite showed 1% variations, while the $^{238}$ U/ $^{206}$ Pb ratio showed 3-24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC-1, with analytical uncertainty as low as 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions, and is a promising alternative to natural calcite RMs for U-Pb geochronology.

Journal Articles

Stabilization of lead with amorphous solids synthesized from aluminosilicate gel

Sato, Junya; Shiota, Kenji*; Takaoka, Masaki*

Journal of Hazardous Materials, 385, p.121109_1 - 121109_9, 2020/03

https://doi.org/10.1016/j.jhazmat.2019.121109

Times Cited Count：12 Percentile：41.69(Engineering, Environmental)

Lead is a hazardous heavy metal that can be stabilized by incorporation into the matrix of aluminosilicate bearing phases as they solidify. The actual mechanism by which lead is stabilized, however, continues to be unclear because the individual mechanisms of Pb incorporation into crystalline and amorphous aluminosilicate phases have not yet been studied separately. A detailed investigation of the incorporation of Pb into the amorphous phase of aluminosilicate solids was therefore performed. Amorphous aluminosilicate solids were synthesized with 0.7, 1.5, and 3.7 wt% of Pb from aluminosilicate gel produced from chemical reagents. Based on Raman spectroscopy, the Si-O stretching vibration bond shifted to lower wavenumbers with increasing Pb concentration. This shift suggested that covalent bonding between Pb and O in the matrix of the aluminosilicate solids increased. In addition, sequential extraction revealed that most of the Pb (75-90%) in the aluminosilicate solids was in a poorly soluble form (i.e. reducible, oxidizable, and residual fractions). These findings indicate that most of Pb is bonded covalently to the amorphous phase in aluminosilicate solids.

Journal Articles

A Thermodynamic model for ZrO $_{2}$ (am) solubility at 25 $^{circ}$ C in the Ca $^{2+}$ -Na $^{+}$ -H $^{+}$ -Cl $^{-}$ -OH $^{-}$ -H $_{2}$ O system; A Critical review

Rai, D.*; Kitamura, Akira; Altmaier, M.*; Rosso, K. M.*; Sasaki, Takayuki*; Kobayashi, Taishi*

Journal of Solution Chemistry, 47(5), p.855 - 891, 2018/05

https://doi.org/10.1007/s10953-018-0766-4

Times Cited Count：11 Percentile：10.39(Chemistry, Physical)

We have critically reviewed experimental data for Zr hydrolysis constant values for formation of several mononuclear and polynuclear species and a solubility product value for ZrO $_{2}$ (am). We have determined new/revised values for the formation constants of Zr(OH) $_{2}$ $^{2+}$ , Zr(OH) $_{4}$ (aq), Zr(OH) $_{5}$ $^{-}$ , Zr(OH) $_{6}$ $^{2-}$ and Ca $_{3}$ Zr(OH) $_{6}$ $^{4+}$ , and the solubility product for ZrO $_{2}$ (am) after the critical review.

Journal Articles

Thermodynamic model for Zr solubility in the presence of gluconic acid and isosaccharinic acid

Kobayashi, Taishi*; Teshima, Takeshi*; Sasaki, Takayuki*; Kitamura, Akira

Journal of Nuclear Science and Technology, 54(2), p.233 - 241, 2017/02

https://doi.org/10.1080/00223131.2016.1255573

Times Cited Count：8 Percentile：57.53(Nuclear Science & Technology)

Zr solubility in the presence of gluconic acid (GLU) and isosaccharinic acid (ISA) was investigated as a function of hydrogen ion concentration (pH $_{rm c}$ ) and the total concentration of GLU or ISA. The dependence of the increase in Zr solubility on the pH $_{rm c}$ and GLU concentration suggested the existence of Zr(OH) $_{4}$ (GLU) $_{2}$ $^{2-}$ in the neutral pH region and Zr(OH) $_{4}$ (GLU)(GLU $_{rm -H}$ ) $^{3-}$ in the alkaline pH region above pH $_{rm c}$ 10 as the dominant species in the presence of 10 $^{-3}$ - 10 $^{-1}$ mol/dm $^{3}$ (M) GLU. In the presence of ISA, the dominant species Zr(OH) $_{4}$ (ISA) $_{2}$ $^{2-}$ and Zr(OH) $_{4}$ (ISA)(ISA $_{rm -H}$ ) $^{3-}$ were proposed to occur in the neutral and alkaline pH regions, similar to those found in the presence of GLU. From X-ray diffraction analysis, the solubility-limiting solid phase in the presence of GLU and ISA was considered to be Zr(OH) $_{4}$ (am). The formation constants of the Zr gluconate and isosaccharinate complexes were determined by least squares fitting analysis of the solubility data, and the obtained values were discussed in comparison with those of tetravalent actinides.

Journal Articles

Incident angle dependence of MCD at the Dy $_{5}$ -edge of perpendicular magnetic Dy $_{x}$ Co $_{100-x}$ films

Agui, Akane; Mizumaki, Masaichiro*; Asahi, Toru*; Sayama, Junichi*; Matsumoto, Koji*; Morikawa, Tsuyoshi*; Matsushita, Tomohiro*; Osaka, Tetsuya*; Miura, Yoshimasa*

Journal of Alloys and Compounds, 408-412, p.741 - 745, 2006/02

https://doi.org/10.1016/j.jallcom.2004.11.077

Times Cited Count：7 Percentile：45.46(Chemistry, Physical)

no abstracts in English

Journal Articles

Coarsening dynamics and surface instability during ion-beam-assisted growth of amorphous diamondlike carbon

Zhu, X. D.; Naramoto, Hiroshi; Xu, Y.; Narumi, Kazumasa; Miyashita, Kiyoshi*

Physical Review B, 66(16), p.165426_1 - 165426_5, 2002/10

https://doi.org/10.1103/PhysRevB.66.165426

Times Cited Count：14 Percentile：56.87(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Modification of carbon related films with energy beams

Naramoto, Hiroshi; Xu, Y.; Narumi, Kazumasa; Vacik, J.; Zhu, X.; Yamamoto, Shunya; Miyashita, Kiyoshi*

Materials Research Society Symposium Proceedings, Vol.647, p.O5.18.1 - O5.18.16, 2001/00

no abstracts in English

Journal Articles

EXAFS study on local structural changes in amorphous Fe-Zr-B alloys

Nakata, Yoshiyuki*; Hara, Naoyuki*; Hirotsu, Yoshihiko*; Emura, Shuichi*; Makino, Akihiro*; Uruga, Tomoya*; Harada, Makoto*; Nishihata, Yasuo; Yoneda, Yasuhiro; Kubozono, Yoshihiro*

Japanese Journal of Applied Physics, 38(Suppl.38-1), p.404 - 407, 1999/06

The EXAFS spectra on Zr K-edge are investigated for as-formed Fe-7at%Zr-3at%B amorphous alloys and annealed ones at 693 K and 773 K for an hour in order to reveal local structural changes due to annealing. The analysis shows that the atomic distances of Fe-Zr and Zr-Zr pairs increase during annealing and approach those in a Fe3Zr or/and Fe2Zr metallic comound. The change in the atomic distances suggests that medium range ordered clusters should be formed during annealing.

Journal Articles

Effect of pressure on hopping conduction in amorphous Ge alloys

Toda, Naohiro*; Katayama, Yoshinori; Tsuji, Kazuhiko*

Review of High Pressure Science and Technology, 7, p.647 - 649, 1998/03

http://ci.nii.ac.jp/naid/10002691304

The electrical conductivity has been measured at pressures to 8 GPa and temperatures of 77-300K in evaporated amorphous Ge (a-Ge), a-Ge-Cu alloys and a-Ge-Al alloys. The dependence of is well described by a power lw at low temperatures below 150 K, which is expemcted from a multi-phonon tunneling transition process model with weak electron-lattice coupling, rather than the Mott's variable range hopping conduction model. The exponent in the power law changes with increasing pressure. For both a-Ge $_{1-x}$ Cu $_{x}$ and a-Ge $_{1-x}$ Al $_{x}$ alloys, d(ln )/d show positive values in the low pressure region and negative values in the high pressure region. Results are discussed from several hopping conduction models.