Materials Science Forum Vols. 449-452

Abstract: Magnetic tunnel junctions(MTJ) are fabricated as a function of the input power of Al thin film. Al thin films have pseudo-crystalline structure at 30, 60, 90 W and transform into amorphous like smooth nanocrystalline state at 120 W. Junction resistance increases as the annealing temperature increases up to 250 􀀀 and decrease at 300 􀀀 at the pseudo-crystalline barrier. When the barrier has amorphous like nanocrystalline structure, optimum annealing temperature increases up to 300 􀀀 . The barrier characteristics are strongly related with the microstructure of AlOx barrier.

Abstract: Effect of washing step in R-D process on the structure and magnetic properties of Nd-Fe-B powder fabricated by the process using a spray-dried precursor was investigated. Although the powder washed in water contained much more residual CaO than that washed in dilute acetic acid, magnetic properties of the former were much better than those of the latter due to less removal of Nd-rich phase. In the powder washed in water Nd2Fe14B particles were enclosed with thin layer of Nd-rich phase, and each particle consisted of one or more subgrains of the size 50 ~ 100 nm or more. Milling the powder before water washing was effective to remove more CaO, thereby increased the remanence of the powder.

Abstract: The magnetotransport properties of the electroplated and sputtered Bi thin films have been investigated in the range 4 – 300 K. A marked increase from 5,200 % to 80,000 % in the ordinary magnetoresistance (MR) for the electroplated Bi thin film was observed after thermal anneal at 4 K. The MR ratios for the as-grown and the annealed Bi thin films were found to exhibit 560 % and 590 %, respectively, at 300 K. On the other hand, the MR for the sputtered Bi film grown by sputtering was hardly observed at 4 and 300 K, whereas the MR ratios after anneal were found to reach 30,000 % at 4 K and 600 % at 300 K. We find that the room temperature MR in the sputtered films depends on the trigonal-axis oriented microstructures and grain size, in contrast to the electroplated films. Our results demonstrate the very large room temperature MR in the electroplated and sputtered Bi thin films, which can be used for spintronic device applications.

Abstract: By using the sputtering process, we made the IrMn based specular spin valve system, whose nano-oxide layer (NOL) was formed by natural oxidation. After thermal annealing at 305 and 410 °C, the thermal stability of the specular spin valve was observed. We found that the highest magnetoresistance (MR) ratio of about 12 % MR was produced after optimum annealing at 305 °C but the sample annealed at 410 °C also had a high MR ratio about 10 %. It is superior to other studies at this temperature. Based on the AES and XPS results, we could conclude that this enhanced thermal stability was due to the stable Cu layer between the pinned layer and free layer and to the NOL as a diffusion barrier for the Mn.

Abstract: Anisotropy magneto-resistance and planar Hall-effect of ferromagnetic GaMnAs epitaxial films were investigated. The films were grown on 2 o off-cut GaAs (001) substrate in an optimized growth condition via low temperature molecular beam epitaxy. The GaMnAs layer revealed an easy axis along the (2x4) reconstruction direction of the substrate or along the off-cut direction. The large value of the anisotropy magneto-resistance ratio of ~7 % was realized by a well-alignment of the easy axis of the homogeneous ferromagnetic GaMnAs layer with the current. It also gives a very high planar Hall resistance ratio of ~500 %.

Abstract: Yttrium Iron Garnet (YIG) has been used as an important material in the Circulator/Isolator which is used in RF communication system, mobile phone, and satellite broadcasting, etc. In this study, we investigated the variation of electromagnetic properties of YIG ferrites for Isolator/Circulator application with Zr addition. The YIG ferrites, Y2.1Ca0.9Fe4.4-xV0.5In0.05Al0.05ZrxO12 with x=0, 0.05, 0.1 and 0.2, were prepared by the conventional ceramic sintering process. The Zr-substituted YIG ferrite, Y2.1Ca0.9Fe4.4-xV0.5In0.05Al0.05ZrxO12, showed the highest saturation magnetization (1097 gauss) at x=0.1. Good microwave properties were shown as isolation of 18.60 dB and insertion loss of 0.45 dB at x=0.2. In addition, the ferromagnetic resonance (FMR) linewidth decreased as Zr content increased

Abstract: The spin transport in a lateral spin-injection device with an FeCo/Si/FeCo junction has been investigated. Magnetoresistance (MR) signals were found to appear at low magnetic fields in the range 4 – 300 K. This is attributable to the switching of the magnetization of the two ferromagnetic contacts in the device for certain magnetic fields over which the magnetization in one contact is aligned antiparallel to that in the other. Our results suggest that the spin-polarized electrons are injected from the first contact and, after propagating through the bulk Si, are collected by the second contact.

Abstract: Ingots of ferritic stainless steels, Fe-24Cr and Fe-24Cr-2Mo in mass%, were worked to various dimensions for test specimens. Nitrogen was absorbed by the specimens in a furnace filled with nitrogen gas with a pressure of 101.3 kPa at 1473 K to develop a simple and convenient manufacturing process of nickel-free austenitic stainless steels. Ferritic Fe-24Cr and Fe-24Cr-2Mo were austenitized with nitrogen absorption to a 2-mm depth from the surface. The hardness, tensile strength, 0.2% proof stress, and elongation to fracture increased, and the reduction of area decreased in the alloys by austenitization due to nitrogen absorption. The tensile strength and 0.2% proof stress of these alloys with nitrogen absorption for 129.6 ks were much larger than those of 316L steel, while the elongation to fracture was much smaller than that of 316L steel. Therefore, small devices and parts with a maximum thickness or diameter of 4 mm were manufactured with this process in this study

Abstract: The effect of Ta content on the mechanical properties of the quenched binary Ti
Ta alloys with different mass percentage of Ta from 10 to 80% was investigated in order to find a Ta content that gives a good balance of low modulus and high strength for biomedical applications. The mechanical properties of binary Ti
Ta alloys depend strongly on the microstructures caused by Ta content. Among all the studied Ti–Ta alloys, Ti
30 mass % Ta alloy with martensite ” and Ti
70 mass % Ta alloy with metastable  phase have the potential to be the new candidates for biomedical applications