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ABSTRACT: The relation between critical current, critical field, and thermal stability of domain wall (DW) trapped at step pinning sites was studied using Co/Ni nanowires with perpendicular magnetic anisotropy (PMA). A sharp step structure was fabricated, which increased the critical field of DW motion, while the critical current was independent of the critical field. Also, the derived thermal stability (ΔE/k<sub>B</sub>T) for the step samples was much more than 60. These results indicate that the DW motion in PMA nanowires has potential for memory devices with both a small driving current and large thermal stability.
Journal of Applied Physics 01/2011; · 2.17 Impact Factor
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ABSTRACT: We observed magnetic configuration and its change by external magnetic fields in submicron-sized U- and H-shaped NiFe patterns with an x-ray magnetic circular dichroism photoemission electron microscope. The microscope images showed the formation of a single domain wall (DW) with transverse structure at one corner of the U- and H-shaped patterns by applying the magnetic field from the oblique direction. By applying the magnetic field from the direction parallel to a horizontal bar in the patterns, the magnetic configuration in the U-shaped pattern was changed and four patterns were formed: (1) the DW moved from one trap site to another, (2) the DW moved beyond the trap site and formed a single domain, (3) the DW moved and stopped between the trap sites, and (4) the DW remained at the initial position. Only pattern (1) showed reversible DW motion, although pattern (2) was predominantly formed. In contrast, the magnetization configurations showed pattern (1), and reversible DW motion was observed for more than 80% of the H-shaped patterns. Micromagnetic simulation revealed that the DW in the U-shaped pattern was not sufficiently fixed at the corner and easily moved and vanished at the edge of the patterns because the magnetization in the two parallel bars rotated with a magnetic field. The DW was trapped with sufficient strength at the corner, and DW motion occurred only between the trap sites for the H-shaped patterns. The DW motion process was observed with an in situ magnetic field using the x-ray magnetic circular dichroism photoemission electron microscope and the process could be optimized by controlling the pattern shape.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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Ryusuke Nebashi,
Noboru Sakimura,
Hiroaki Honjo,
Shinsaku Saito,
Yuichi Ito,
Sadahiko Miura,
Yuko Kato,
Kaoru Mori,
Yasuaki Ozaki,
Yosuke Kobayashi,
Norikazu Ohshima,
Keizo Kinoshita,
Tetsuhiro Suzuki,
Kiyokazu Nagahara, Nobuyuki Ishiwata,
Katsumi Suemitsu,
Shunsuke Fukami,
Hiromitsu Hada,
Tadahiko Sugibayashi,
Naoki Kasai
IEEE International Solid-State Circuits Conference, ISSCC 2009, Digest of Technical Papers, San Francisco, CA, USA, 8-12 February, 2009; 01/2009
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Yoshiyuki Fukumoto,
Tetsuhiro Suzuki,
Kaoru Mori,
Hiroaki Honjo,
Chuji Igarashi,
Norikazu Ohshima,
Sadahiko Miura, Nobuyuki Ishiwata,
Shuichi Tahara,
Yoshiaki Asao,
Hiroaki Yoda
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ABSTRACT: We developed synthetic antiferromagnets (SAFs) with a multilayer structure where more than three magnetic layers were coupled in an antiparallel configuration for use as a free layer of toggle magnetic random access memories, with the aim of reducing the switching field. The SAFs consisted of a magnetic layer of NiFe/CoFe with a spacer layer of Ru and were deposited on the Al-oxide barrier layer in magnetic tunnel junctions. Conventional bilayer SAFs did not realize a large writing margin with a low spin flop field (Hflop). On the other hand, multilayer SAFs increased the saturation field (Hs) significantly with increases in both the number of magnetic layers (N) and the antiferromagnetic coupling (AFC) strength between the inner magnetic layers while maintaining a low Hflop. This is because strong AFCs involved in the inner magnetic layers and weak AFCs of the outer magnetic layers determine Hs and Hflop of these, respectively. To control an AFC of each spacer layer, we chose an appropriate thickness for each Ru layer in the multilayer SAFs according to the Ru crystalline structure that was responsible for its AFC strength.
Journal of Applied Physics 04/2006; 99(8):08N905-08N905-3. · 2.17 Impact Factor
