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103. Atomic-scale quantitative analysis of implanted Mg in annealed GaN layers on free-standing GaN substrates.

Author

Kumar, Ashutosh, Uzuhashi, Jun, Ohkubo, Tadakatsu, Tanaka, Ryo, Takashima, Shinya, Edo, Masaharu, and Hono, Kazuhiro

Subjects
MAGNESIUM ions, SCANNING transmission electron microscopy, ATOM-probe tomography, QUANTITATIVE research, INDIUM gallium nitride, GALLIUM nitride
Abstract

Achieving efficient p-type conduction in Mg-implanted GaN depends largely on postimplantation annealing conditions. Here, we study the effect of postimplantation annealing on the evolution of defects and their interactions with implanted Mg ions by using scanning transmission electron microscopy and atom probe tomography. We found that Mg clusters start to form by annealing the implanted sample above 1000 °C. In addition to the Mg clusters, stacking faults form at an annealing temperature of 1300 °C. The Mg concentrations of about 2–3 orders of magnitude higher than implanted Mg were segregated at the stacking faults. Nanobeam electron diffraction analysis revealed no distinct phase other than GaN formed at the Mg-enriched defects, suggesting that Mg is substituted for Ga in the GaN lattice at the edge of the stacking faults. [ABSTRACT FROM AUTHOR]

Published
2019
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113. Microstructure Origin of the Large Coercivity in an (Nd, Dy)-Fe-B Sintered Magnet

Author

Tang, Xin, primary, Li, J., additional, Sepehri-Amin, Hossein, additional, Bolyachkin, Anton, additional, Martin-Cid, A., additional, Kobayashi, S., additional, Kotani, Yoshinori, additional, Suzuki, M., additional, Terasawa, A., additional, Gohda, Y., additional, Ohkubo, Tadakatsu, additional, Nakamura, Tetsuya, additional, and Hono, Kazuhiro, additional

Published
2022
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115. Structural Insight Using Anomalous XRD into Mn 2coal Heusler Alloy Films Grown by Magnetron Sputtering, IBAS, And MBE Techniques

Author

Tajiri, Hiroo, primary, Kumara, Loku Singgappulige Rosantha, additional, Sakuraba, Yuya, additional, Chen, Zixi, additional, Wang, Jian, additional, Zhou, Weinan, additional, Varun, Kushwaha, additional, Ueda, Kenji, additional, Yamada, Shinya, additional, Hayama, Kohei, additional, and Hono, Kazuhiro, additional

Published
2022
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117. Analysis of magnetotransport properties and microstructure in current-perpendicular-to-plane pseudo spin-valves using Co2Fe(Ga0.5Ge0.5) Heusler alloy and Ag/Mg-Ti-O/Ag-based spacer.

Author

Du, Ye, Sakuraba, Yuya, Nakatani, Tomoya, Furubayashi, Takao, Sasaki, Taisuke, Takahashi, Yukiko K., and Hono, Kazuhiro

Subjects
MAGNETORESISTANCE, MICROSTRUCTURE, MAGNETIZATION, ELECTRIC potential, OXIDES
Abstract

Current-perpendicular-to-plane magnetoresistance (CPP-MR) devices using a Co2Fe(Ga0.5Ge0.5) Heusler alloy as ferromagnetic electrodes and a Ag/Mg-Ti-O (MTO)/Ag tri-layer as a spacer are studied. A large voltage output of 16 mV with a magnetoresistance ratio of 46% and resistance-area product RpA in the parallel magnetization state of approximately 200 mΩ μm2 are obtained. The microstructure characterization reveals that upon annealing at 550 °C, nanoscale Ag channels are formed penetrating the MTO layer, which are responsible for the large MR output. At room temperature, for all the devices, RpA decreases with increasing the bias voltage Vb, which is contradictory to the conventional CPP-giant magnetoresistance devices with a current-confined-path structure, in which the RpA increases with increasing Vb. Such a Vb dependence of RpA is in accordance with the temperature dependence of RpA. These results suggest that the magneto-transport channels comprise semiconducting current confined paths, bringing new perspectives for the design and engineering of CPP-MR devices with conductive oxides-based multilayer spacers. [ABSTRACT FROM AUTHOR]

Published
2018
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130. High L21-atomic ordering and spin-polarization in Co2MnZ (Z = Ge, Sn) Heusler thin films with low-temperature annealing process.

Author

Kushwaha, Varun Kumar, Sakuraba, Yuya, Nakatani, Tomoya, Sasaki, Taisuke, Kurniawan, Ivan, Miura, Yoshio, Tajiri, Hiroo, and Hono, Kazuhiro

Subjects
THIN films, ENHANCED magnetoresistance, TIN, ELECTRIC currents, TRANSITION temperature, HEUSLER alloys, FERROELECTRIC thin films
Abstract

Although an enhanced magnetoresistance (MR) has been observed in many Co2-based Heusler alloys by promoting their structural ordering from B2 to L21 by post-annealing at higher temperatures (Tann > 500 °C), it is desirable to search for other Heusler alloys that crystallize in L21-order below 300 °C, as the maximum Tann is restricted for processing devices. For Co2MnZ (Z = Ge, Sn) Heusler alloys, an L21-order is expected to appear even in the as-deposited state or by a low-temperature annealing process due to their very high L21 to B2-order transition temperature (>1500 K). Here, epitaxial Co2MnZ films were grown on MgO (001) substrate at room temperature (RT) and post-annealed at Tann = 200–500 °C. Interestingly, as-sputtered films exhibit L21-ordering, which improves systematically upon increasing Tann. The spin-polarization of electric current (β) was estimated at RT using nonlocal spin-valve (NLSV) devices by measuring the spin-accumulation signal in a copper (Cu) channel. It was found that at Tann = 300 °C, the β value of Co2MnGe films is higher (∼0.65) than that of Co2FeGe0.5Ga0.5 films due to a higher degree of L21-order, which makes the Co2MnGe alloy a promising ferromagnetic electrode for spintronic device applications. [ABSTRACT FROM AUTHOR]

Published
2022
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131. Process parameters and magnetic properties (coercivity, remanence, squareness, maximum energy product) of data-driven fabrication of Nd-Fe-B anisotropic magnets by direct hot extrusion.

Author

0000-0003-0275-4079, Lambard, Guillaume, 0000-0002-5952-7638, Sasaki, Taisuke, 0000-0002-9228-0729, Sodeyama, Keitaro, 0000-0003-3548-1951, Ohkubo, Tadakatsu, 0000-0001-7367-0193, Hono, Kazuhiro, 0000-0003-0275-4079, Lambard, Guillaume, 0000-0002-5952-7638, Sasaki, Taisuke, 0000-0002-9228-0729, Sodeyama, Keitaro, 0000-0003-3548-1951, Ohkubo, Tadakatsu, 0000-0001-7367-0193, and Hono, Kazuhiro

Published
2021

133. Large linear sensitivity of asymmetric structured giant magnetoresistive device with metastable bcc-Cu spacer and auxiliary biquadratic coupling through Rh spacer

Author

Taparia, Dolly, primary, Fathoni, Kresna Bondan, additional, Kulkarni, Prabhanjan Dilip, additional, Srinivasan, Ananthakrishnan, additional, Alagarsamy, Perumal, additional, Sakuraba, Yuya, additional, Nakatani, Tomoya, additional, Sasaki, Taisuke, additional, and Hono, Kazuhiro, additional

Published
2021
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136. Impact of oxygen on band structure at the Ni/GaN interface revealed by hard X-ray photoelectron spectroscopy

Author

Mizushima, Hirotaka, primary, Arai, Ryoji, additional, Inaba, Yuta, additional, Yamashita, Shunsuke, additional, Yamaguchi, Yudai, additional, Kanitani, Yuya, additional, Kudo, Yoshihiro, additional, Hamaguchi, Tatsushi, additional, Koda, Rintaro, additional, Yanashima, Katsunori, additional, Ohkubo, Tadakatsu, additional, Hono, Kazuhiro, additional, and Tomiya, Shigetaka, additional

Published
2021
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145. Mg diffusion and activation along threading dislocations in GaN

Author

Yi, Wei, primary, Kumar, Ashutosh, additional, Uzuhashi, Jun, additional, Kimura, Takashi, additional, Tanaka, Ryo, additional, Takashima, Shinya, additional, Edo, Masaharu, additional, Yao, Yongzhao, additional, Ishikawa, Yukari, additional, Chen, Jun, additional, Ohkubo, Tadakatsu, additional, Sekiguchi, Takashi, additional, and Hono, Kazuhiro, additional

Published
2020
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147. Advanced CPP-GMR Spin-Valve Sensors for Narrow Reader Applications

Author

Nakatani, Tomoya, Sakuraba, Yuya, Furubayashi, Takao, and Hono, Kazuhiro

Abstract

The near-future ultra-high-density magnetic recording with an assist recording technology requires a substantial evolution of the read-head technology. A read sensor with a small sensor resistance-area product (RA), a large magnetoresistance ratio (ΔR/R), and a thin total sensor thickness is required for the low bit error rate and high-spatial resolution of reading. We developed current-perpendicular-to-plane giant magnetoresistance sensors using highly spin-polarized Heusler alloy ferromagnetic layers with the spin polarization of the conducting electron β ~ 0.8. A reasonably large ΔR/R up to 14% was obtained by a practical bottom-pinned spin-valve structure with a conventional metallic spacer layer of an Ag 90 Sn 10 (AgSn) alloy. By replacing the spacer layer with a conductive oxide-based AgSn/InZnO bilayer, a large ΔR/R up to 32% was realized at RA value of ~0.1 Ω · μm 2 , which is optimal for the read sensor application. A large voltage output up to 6 mV was obtained for a sensor utilization of ~33% at a bias voltage of 100 mV.

Published
2018

148. Development of Co-lean (Sm,Y)(Fe,Co,Ti)12 compounds with large saturation magnetization.

Author

Tozman, Pelin, Sepehri-Amin, Hossein, Tang, Xin, Ohkubo, Tadakatsu, and Hono, Kazuhiro

Abstract

Large saturation magnetization in the SmFe12-based compounds is realized by substitution of scarce Co for Fe site. However, reduction of Co is necessary for their potential practical applications. In this work, we successfully decrease the concentration of Co, from 17.3 at% to 8.7 at% while maintaining large μ 0 M s of 1.41 T at 300 K in Ti reduced Sm0.8Y0.2(Fe0.9Co0.1)11.25Ti0.75 compound. In addition, we report the highest μ 0 M s for bulk Sm0.8Y0.2(Fe0.8Co0.2)11.25Ti0.75 with μ 0 M s  = 1.49 T, μ 0 H a  = 9.14 T at 300 K and T c = 831 K. We demonstrate (Sm0.8Y0.2)Fe12-based compounds exhibit superior intrinsic magnetic properties than Nd2Fe14B above 473 K. [ABSTRACT FROM AUTHOR]

Published
2022
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150. Order parameters and magnetocrystalline anisotropy of off-stoichiometric D022 Mn2.36Ga epitaxial films grown on MgO (001) and SrTiO3 (001).

Author

Hwachol Lee, Sukegawa, Hiroaki, Mitani, Seiji, and Hono, Kazuhiro

Subjects
ANISOTROPY, MATHEMATICAL models, MAGNETIC anisotropy, PROPERTIES of matter, MAGNETIC properties of thin films, RANDOM access memory, MAGNETIC fields, CHARTS, diagrams, etc.
Abstract

We study the relationship between long range order parameters and the magnetocrystalline anisotropy of off-stoichiometric D022 Mn2.36Ga (MnGa) epitaxial films grown on MgO (001) and SrTiO3 (STO) (001) single crystalline substrates. MnGa films deposited on MgO (001) show rather large irregular variation in magnetization with increasing substrate temperature in spite of the improved long range order of total atomic sites. The specific site long range order of Mn-I site characterized in the [101] orientation revealed the fluctuation of the occupation fraction of two Mn atomic sites with elevated substrate temperature, which appears more relevant to the observed magnetization change than the long range order of the total atomic sites. In case of MnGa films grown on the lattice-matched STO (001), high long range order of the total atomic sites in spite of the existence of secondary phase represents that the lattice mismatch plays a crucial role in determining the atomic arrangement of Mn and Ga atoms in the off-stoichiometric compositional case of MnGa. [ABSTRACT FROM AUTHOR]

Published
2015
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