Journal of the Magnetics Society of Japan
Online ISSN : 1882-2932
Print ISSN : 1882-2924
ISSN-L : 1882-2924
36 巻, 5 号
選択された号の論文の3件中1~3を表示しています
薄膜,微粒子,多層膜,人工格子
  • 鎌田 真之, 藏 裕彰, 高橋 研, 小川 智之, 田中 寿郎
    2012 年 36 巻 5 号 p. 309-312
    発行日: 2012/09/01
    公開日: 2012/09/26
    ジャーナル オープンアクセス
      Magnetic nanoparticles (NPs) have attracted attention for their potential use electronic devices and nano -bioengineering applications. Fe NPs made from an Fe(CO)x-Oleylamine (OlAm) reacted precursor by thermal decomposition show high saturation magnetization (σs) (∼140 emu/gnet at 300 K). However, the σs never reaches the bulk value (218 emu/g at 300 K) of iron. This is due to the unique crystalline structure of the Fe NPs. Fe NPs covered with OlAm (OlAm-Fe NP) have an expanded α(b.c.c.) structure and ultra-fine grains. We improved the σs of Fe NPs via phase control by adjusting the adsorption ability of a surfactant such as trioctylamine (TOcAm) or tribenzylamine (TBeAm). These surfactants have weaker adsorption ability than that of OlAm. Rietveld analysis revealed that the crystalline structure of Fe NPs covered with TOcAm or TBeAm was drastically changed into a rather α-Fe phase, in contrast to the expanded α phase observed for the OlAm-Fe NPs. TOcAm-Fe NPs had 10- 80 vol.% of the α-Fe phase, and TBeAm-Fe NPs had 80- 99 vol.% of the α-Fe phase, which indicates an α-Fe single phase. A σs of 199 emu/gnet for the TBeAm-Fe NPs was obtained at 300 K. This remarkable improvement is due to the increase volume fraction of the α-Fe phase. These results suggest that α-Fe phase formation using weak adsorption surfactant was highly effective for improving the σs.
  • 高橋 宏和, 角田 匡清, 高橋 研
    2012 年 36 巻 5 号 p. 313-317
    発行日: 2012/09/01
    公開日: 2012/09/26
    [早期公開] 公開日: 2012/07/27
    ジャーナル オープンアクセス
      The dependence of perpendicular exchange anisotropy on the thickness of the ferromagnetic (FM) layer in Mn-Ir / [Co/Pt]n multilayers was investigated. The dependencies on temperature of saturation magnetization, Ms, in [Co / Pt]n multilayers having Co and Pt layers of various thicknesses were examined. The rate of decrease of Ms against temperature was large for thin-Co (< 1 nm) or thick-Pt layers ( > 1 nm), which indicates that thermal fluctuations in magnetization were significant. The unidirectional anisotropy constant, JK, was reduced with the decreasing thickness of the interfacial Co layer in contact with the Mn-Ir layer. This suggested that perpendicular exchange bias was degraded by thermal fluctuations in FM magnetization during thermal annealing. The dependencies of JK on the thicknesses of the Pt layer and inner Co layer could be also described by the thermal fluctuations in the magnetization of the FM layer.
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