論文 - 能崎　幸雄

Numerical study for successive ballistic motion of magnetization in single domain particle caused by alternating magnetic fields

Y. Nozaki, K. Matsuyama

INTERMAG 2006 - IEEE International Magnetics Conference    923 2006年

筆頭著者, 最終著者, 責任著者, 査読有り

• Access to Document (DOI)

Thickness dependence of interlayer fringe field coupling in sub micron NiFe/Cu multilayered pillars.

M. Zhang, Y. Nozaki, and K. Matsuyama

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  41 （ 10 ） 2583 – 2585 - 1744 2005年10月

研究論文（学術雑誌）, 共著, 査読有り

• Access to Document (DOI)

Thickness dependence of interlayer fringe-field coupling in submicrometer NiFe/Cu multilayered pillars

M Zhang, Y Nozaki, K Matsuyama

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  41 （ 10 ） 2583 - 2585 2005年10月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

The effect of fringe-field coupling on the magnetization reversal process in submicrometer scale giant magnetoresistive pillars consisting of [NiFe/Cu](6) has been investigated by means of current perpendicular to plane magnetoresistance measurements and numerical simulations. The parabolic and reversible magnetoresistance curves due to an opposite rotation of magnetization in neighboring NiFe layers were observed. To explain the field sensitivity of the pillars quantitatively, we have proposed a modified single-domain model, where the magnetic energy of the system is reconstructed using the result of the micromagnetic simulation of a magnetostatically coupled bilayer system. The calculated magnetoresistance curves are consistent with the experimental ones. From the calculated results, the amplitude of the saturation field is found to be proportional to the thickness of the ferromagnetic layer and inversely proportional to the square root of the nonmagnetic layer thickness.

• Access to Document (DOI)

Numerical simulation of write-operation in MRAM memory cell array with magnetostatic interaction

Y. Nozaki, S. Nagayasu, S. Ishii, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  97 （ 10 ） 10P505 (1-3) 2005年05月

研究論文（学術雑誌）, 共著, 査読有り

CPP transport properties of polycrystalline Fe3O4 thin films sputtered on Cu underlayers

F. Qin, Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  97 （ 10 ） 10C315 (1-3) 2005年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Transport properties of sputtered Fe3O4 thin films have been studied with the current perpendicular to plane (CPP) configuration. Fabricated polycrystalline Fe3O4 films exhibit superior CPP conductivity of 12 k Omega(-1) center dot m(-1). In addition to the Verwey transition (VT), observed at 114 K, another type of drastic conductivity change [field induced transition (FT)] was observed at lower temperature (T < 70 K) and higher bias voltage (V-b > 0.18 V) regime. The conductivity change at FT is discontinuous and several orders in magnitude. The transition temperature for FT presents considerable Vb dependence, contrarily no distinguished dependence for VT. (c) 2005 American Institute of Physics.

• Access to Document (DOI)

Numerical simulation of write-operation in a magnetic random access memory cell array with a magnetostatic interaction

Y Nozaki, H Terada, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  97 （ 10 ） 10P505 (1-3) 2005年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

The margin for selective write-operation in a current coincident scheme has been numerically evaluated by considering a magnetostatic interaction in a magnetic random access memory cell array. For a conventional method, the margin over 20% cannot be achieved as the cell size is smaller than 0.2 x 0.4 mu m(2). This is mainly attributed to the degradation of field localization created by a conductor current. The minimum cell size ensuring the practical margin can be decreased to 0.16 x 0.24 mu m(2) by using an opposing current flowing through neighboring conductors. The margin is found to be remarkably decreased as a current pulse width becomes less than 0.4 ns because of a gyromagnetic effect. (c) 2005 American Institute of Physics.

• Access to Document (DOI)

Fabrication and characterization of ferromagnetic tunnel junction with transition metal oxides.

F. Qin, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  10 （ 2 ） 63 – 66 - 66 2005年03月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

　概要を見る

A novel ferromagnetic tunnel junction with transition metal oxides has been fabricated with photo-lithographic technique. Well defined tunneling properties were observed in a novel barrier material of TiO_x with the thickness down to 2 nm. Spin dependent transport properties have been confirmed for Fe_3O_4/ TiO_x/M (M =Co, Co/NiFe, NiFe) tunnel junctions, where highest magneto-resistance (MR) change of 7% was observed for Co. Drastic improvement of field sensitivity was attained with the exchange coupled Co/NiFe bi-layer.

• Access to Document (DOI)

Electrically induced conductivity switching in sputtered Fe3O4 thin film.

F. Qin, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  9 （ 2 ） 85 – 88 - 88 2004年09月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

　概要を見る

Electric transport properties have been studied for Fe_3O_4 thin films with current perpendicular to plane geometry, aiming at development of oxide spintronics devices. Excellent conductivity comparable to a bulk single crystal was attained by optimizing an under layer material and film deposition condition. A novel conductivity switching, up to three orders of magnitude, was observed. The threshold value of electric field for switching and its temperature dependence were investigated.

• Access to Document (DOI)

Effect of metallic under-layer on structural and magnetic properties of sputtered Fe3O4 films

F. Qin, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1835 – e1837 - E1837 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

High-quality Fe3O4 films are fabricated on glass substrates with metallic underlayers of Cr/Cu or Al by RF magnetron sputtering at relatively low deposition temperature of 300 degrees C. The measured values of saturation magnetization M-s are 462 emu/cm(3) for Al(50 nm)/ Fe3O4(200 nm) and 422 emu/cm(3) for Cr(45 nm)/ Cu(300 nm)/ Fe3O4(200 nm), which are drastically enhanced compared with that for the reference sample deposited directly on a glass substrate, and practically comparable to the bulk value of 477 emu/ cm(3). (C) 2003 Elsevier B. V. All rights reserved.

• Access to Document (DOI)

Controlling of spin orientation in a pseudo spin valve MRAM cell with pulsed conductor currents

J. Kikuchi, A. Akiyoshi, H. Terada, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   1895 – 1897 - 1897 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Reversal of spin orientation using current-carrying conductors are studied for a micro-structured pseudo-spin valve material of Co79Fe21(3 nm)/Cu(4 nm)/Co73Fe27(4 nm) by magnetoresistive measurements. Selective spin reorientation in one of the two magnetic layers are successfully performed with practical current amplitude smaller than 10 mA/mum. Compositionally differentiated coercive field in the CoFe films would be a dominant cause for the selectivity of the spin reorientation. (C) 2004 Elsevier B.V. All rights reserved.

• Access to Document (DOI)

Thermal stability of Co90Pt10 islands with relief-structured samples

Y. Nozaki, S. Nagayasu, S. Ishii, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1319 – e1321 - E1321 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Thermal stability of submicron scale Co90Pt10 island has been investigated using relief-structured giant magnetoresistive samples. Elongated islands with the lateral dimension of 0.5 mu m x 2.0 mu m and the thickness of 6 nm show nonlinear increase of the coercive field with decreasing temperature. The evaluated energy barrier becomes larger than 80k(B)T for the thickness ranging from 6 to 18 nm. (C) 2003 Elsevier B.V. All rights reserved.

• Access to Document (DOI)

Effect of magnetostatic fringe field coupling on magnetic properties of nano-structured single domain particle arrays

32. H. Oishi, S. Ishii, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1355 – e1357 - E1357 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

We have numerically investigated the co-operative magnetization reversal of magnetic particle arrays with fringe fields coupling. Demagnetization processes of one-dimensional particle arrays are studied taking the inter-particle separation S and uniaxial anisotropy K-u as parameters. Particles are found to rotate toward same or opposite directions depending on the values of S and K-u: (C) 2003 Elsevier B.V. All rights reserved.

• Access to Document (DOI)

Magnetic and electric properties of Fe3O4 thin films sputtered on metallic underlayer

F. Qin, Y. Nozaki, and K. Matsuyama

IEICE Transactions on Electronics （The Institute of Electronics, Information and Communication Engineers）  E87-C （ 2 ） 189 – 192 - 192 2004年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0916-8524

　概要を見る

High-quality Fe3O4 thin films have been fabricated onto metallic underlayers of Cr/Cu and Al by rf-magnetron sputtering at low substrate temperatures (< 573 K). The measured saturation magnetizations M-s are 462 emu/cm(3) for Al (50 nm)/Fe3O4 (200 nm) and 422 emu/cm(3) for Cr (45nm)/Cu (300nm)/Fe3O4 (200nm), which are markedly enhanced compared with that for the reference sample deposited directly on a glass substrate, and practically comparable to the bulk value of 477 emu/cm(3). Highly conductive transport with an order-disorder change of the Verwey transition was observed in the current-perpendicular-to-plane geometry. The order of decrease in coercive field was achieved by exchange coupling with an overlaid NiFe layer.

Non-linear temperature dependence of switching fields in relief-structured Co/Ni80Fe20 particles

Y. Nozaki, K. Matsuyama, and S. Ishii

Journal of Applied Physics （The American Institute of Physics）  93 （ 11 ） 9182 – 9185 - 9185 2003年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The temperature dependence of the switching properties in low sub-mum scale Co/Ni80Fe20 particles with different aspect ratios L/w (= 1-6, w = 0.4 mum) and thicknesses t (= 1-5 nm) are investigated using magnetotransport measurements of relief structured. films with giant magnetoresistance. The shape of each particle is a parallelogram with slope angle theta(=0degrees-60degrees). The switching field of the particles increased with theta due to the variation of the end-domain configuration. Nonlinear temperature dependence of the switching field was observed, which could be explained by the thermal nucleation theory of the magnetization reversal at below 150 K. The amplitude of the energy barrier height DeltaE for the reversal was strongly suppressed by decreasing the thickness of the particles. This degradation of the thermal stability may be caused by the variation of the film morphology by decreasing the thickness. (C) 2003 American Institute of Physics.

• Access to Document (DOI)

Switching behavior of cross contacting current perpendicular to plane giant magnetoresistance structure fabricated by two-step ion milling technique

H Oishi, Y Nozaki, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  93 （ 10 ） 7613 - 7615 2003年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

A current perpendicular to plane giant magnetoresistance structure with a cross contact geometry was fabricated by a two-step ion-milling technique. Multilayer pillars with various layer structures and a lateral dimension down to 0.4 mum were embedded between orthogonal top and bottom electrodes. The microfabricated cross point structure minimizes the influence of electrode resistance in measurements of magnetoresistance in current perpendicular to plane geometry. Individual switching of Co layer was observed in a pillar with layer structure of [Co(10 nm)/Cu(4 nm)/Co(2 nm)/Cu(10 nm)](3) and lateral dimension of 0.4x2.0 mum(2). Distinct three-step resistance change was observed for the rising part of the magnetoresistance (MR) curve, corresponding to the switching of Co(2 nm) layers. Somewhat complicated MR behavior in the falling part suggests the existence of a local minimum configuration during the switching of Co(10 nm) layers. The switching behavior of magnetic layers with interlayer dipole coupling was studied by micromagnetic simulations. Markedly different switching field of Co layers can be attributable to the variation of the dipole fields at each layer. (C) 2003 American Institute of Physics.

• Access to Document (DOI)

Size dependence of switching current and energy barrier in the magnetization reversal of rectangular MRAM cell

Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  93 （ 10 ） 7295 – 7297 2003年05月

研究論文（学術雑誌）, 共著, 査読有り

Switching behavior of cross contacting CPP-GMR structure fabricated by two-step ion milling technique

H. Oishi, Y. Nozaki, K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  93 （ 10 ） 7613 – 7615 2003年05月

研究論文（学術雑誌）, 共著, 査読有り

Size dependence of switching current and energy barrier in the magnetization reversal of rectangular magnetic random access memory cell

Y Nozaki, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  93 （ 10 ） 7295 - 7297 2003年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

Write operation in magnetic random access memory (MRAM) with bit density of Gbit/cm2 order has been numerically simulated for low submicron scale magnetic cells. The amplitude of both the switching current I-w and the energy barrier DeltaE of the magnetic cell show strong dependence on the width w and the thickness t of the cell. The calculated results show that the amplitude of I-w is proportional to t/w, while that of DeltaE is proportional to wt(2). To obtain the sufficient energy barrier against a thermal stability (DeltaE>80k(B)T, at 300 K), the thicker magnetic cell is required as the cell is downsized for high-density memory applications, although the thinner one is preferred to lower the switching current. From the calculated results, it appears that the margin of the switching current for selective write operation is decreased with decreasing the lateral aspect ratio of the cell. The addressability for the write operation is also degraded by the formation of structural defect in the cell. In this article, optimum configurations of the magnetic cell applicable for Gbit MRAM are discussed. (C) 2003 American Institute of Physics.

• Access to Document (DOI)

Gbit級MRAM機能動作の計算機シミュレーション

能崎幸雄, 松山公秀

電子情報通信学会技術研究報告 （電子情報通信学会）  102 （ 723 ） 35 – 40 2003年03月

研究論文（学術雑誌）, 共著, 査読有り

Selective writing of sub-um2 domains in spin valve strip with current coincident scheme

K. Matsuyama, Y. Nozaki, J. Kikuchi

Proceedings of International Workshop on Informations & Electrical Engineering (IWIE 2002) （Kyunghee University）  36 （ 5 ） 152 – 157 2002年05月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り