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24 巻, 4_1 号
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菅原 淳一, 中塩 栄治, 尾上 精二, 熊谷 静似2000 年 24 巻 4_1 号 p. 192-195
発行日: 2000年
公開日: 2007/02/26
ジャーナル オープンアクセスThe annealing effect of ferromagnetic tunnel junctions was studied so as to achieve a higher MR ratio for the junction of an NiFe/CoxFe1-x/Al-O/CoxFe1-x/IrMn system. We fabricated NiFe/Co90Fe10/Al-O/Co90Fe10/IrMn junctions (sample 1) using metal masks. Rs increased monotonically with increasing annealing temperature. The MR ratio increased up to 300°C and rapidly decreased as a result of annealing at higher temperatures. The barrier height (φ) increased and the barrier width (d) decreased with increasing annealing temperature. It is thought that a suitable Al-O barrier was formed by annealing and that the MR ratio increased as a result. To obtain more data, we measured the saturated magnetization (Ms). Ms decreased rapidly as a result of annealing over 300°C: this corresponds to the rapid decrease in the MR ratio. Next, we fabricated NiFe/Co75Fe25/Al-O/Co75Fe25/IrMn junctions (sample 2) without breaking the vacuum in the stacking process. The maximum MR ratio.was 49% after annealing at 200°C. The annealing temperature dependence of samples 1 and 2 were quite different.抄録全体を表示PDF形式でダウンロード (310K) -
金清 裕和, 広沢 哲2000 年 24 巻 4_1 号 p. 196-201
発行日: 2000年
公開日: 2007/02/26
ジャーナル オープンアクセスThe effect of co-addition of Cr and Co to Fe3B/Nd2Fe14B exchange-spring nanocomposite permanent magnets on the magnetic properties and their stability was investigated. It was found that HcJ of Fe3B/Nd2Fe14B exchange-spring magnets can be controlled in the range from 300 kA/m to 600 kA/m by adjusting the Cr and Nd concentrations. The squareness of the demagnetizion curves is improved by simultaneous addition of Cr and Co. Thermal stability is also improved by Cr addition: irreversible flux losses rate of the 5 at% Cr-doped Fe3B/Nd2Fe14B exchange-spring magnets were about 1 % after exposure to a temperature of 100°C. This type of magnets are less susceptible to oxidation because the rare-earth content is lower than that of conventional Nd2Fe14B isotropic powders. The higher packing density can be obtained because of the round shape of the pulverized Fe3B/Nd2Fe14B exchange-spring magnet. Consequently, Fe3B/Nd2Fe14B exchange-spring magnet powders are suitable for the injection-molding process in which the magnetic powders are exposed to high temperatures.抄録全体を表示PDF形式でダウンロード (422K) -
藤原 哲也, 藤井 博信, 繁岡 透2000 年 24 巻 4_1 号 p. 202-207
発行日: 2000年
公開日: 2007/02/26
ジャーナル オープンアクセスIn this paper, we report experimental results on the overall magnetic properties of intermetallic compounds Gd1-xLaxMn2Ge2 (0≤x≤1.0) with a ThCr2Si2-type layered structure. In GdMn2Ge2, a first order transition was observed from antiferromagnetic to ferrimagnetic state at Tt3 below TN with decreasing temperature, while in Gd1-xLaxMn2Ge2 with x = 0.075 and 0.050, two kinds of first-order transitions, from ferrimagnetic to antiferromagnetic and from antiferromagnetic to reentrant ferrimagnetic states were observed at Tt2 and Tt3 after they become ferrimagnetic below Tt1. As x further increases canted ferrimagnetism appears with a compensation temperature in all the ordering temperature regions for 0.10 < x < 0.40, whereas no compensation behavior was observed for x > 0.50. The compensation behavior as a function of temperature is discussed on the basis of the two-sublattice molecular-field model.抄録全体を表示PDF形式でダウンロード (462K) -
藤原 哲也, 藤井 博信, 福田 秀孝, 繁岡 透2000 年 24 巻 4_1 号 p. 208-213
発行日: 2000年
公開日: 2007/02/26
ジャーナル オープンアクセスIn this work, we studied the magnetic and transport properties of an intermetallic compound Gd0.925La0.075Mn2Ge2 with a ThCr2Si2-type layered structure. Gd0.925La0.075Mn2Ge2 exhibits canted ferrimagnetism with ferromagnetic and antiferromagnetic components below Tt1 = 348K. With decreasing temperature, it moves into a non-collinear antiferromagnetic state at Tt2 = 244 K, and finally transforms into a reentrant canted ferrimagnet at Tt3 = 142 K. For Tt3 < T < Tt2, a field induced metamagnetism from antiferromagnetism to ferrimagnetism occurs at relatively lower fields, accompanied with fractal like multi-step metamagnetic transitions, the so called “devil’s stair-case”. The appearance of such fractal like multi-step metamagnetic transitions may result from a step-like formation of ferrimagnetic clusters due to spin-flips of Mn moments that occur independently in the antiferromagnet when magnetic fields are applied as well as from a step-like growth of their ferrimagnetic clusters. In addition, a giant magnetoresistance effect (Δρ/ρ∼15%) was also observed at the metamagnetic transition.抄録全体を表示PDF形式でダウンロード (460K)
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