Nobuyasu Adachi

Structure and magnetic properties of high coercive NdFeB films with a perpendicular anisotropy

Relatively good hard magnetic properties obtained from Nd2Fe14B films prepared by the rf sputtering technique were investigated in terms of the microstructural development. Although as-deposited films on Mo substrates deposited at substrate temperatures (Ts) of 365 °C were amorphous with the dispersion of nanocrystalline NdO particles, columnar grains of Nd2Fe14B phase with the c-axis perpendicular to the film plane developed after annealing at 650 °C at an optimized heating rate. Nd2Fe14B grain size was about 400 nm in average and NdO particles of about 10 nm were dispersed within the grains and along the grain boundaries. These films exhibited good perpendicular hard magnetic properties of iHc=1356 kA/m and (BH)MAX∼216 kJ/m3.

Porous ceramics prepared by mimicking silicified wood

Abstract Porous titania, alumina and zirconia ceramic woods with wood-like microstructures, analogous to that of silicified wood, were prepared from natural woods as templates. The production of these ceramic woods was performed by the following process: (1) infiltration of metal alkoxide into wood specimens, (2) hydrolysis of the alkoxide in the cell structure to form titania, alumina or zirconia gels, (3) firing in air to form titania, alumina or zirconia ceramic woods. The resulting titania, alumina and zirconia ceramic woods were studied by means of an X-ray diffractometer, a mercury porosimeter and a scanning electron microscope. The microstructure of these ceramic woods retained the same structure as that of the raw wood: with the pore sizes corresponding to those of the original wood, and the major pores being unidirectionally connected.

Evaluation of Induced Electromotive Force of a Carbon Micro Coil

The magnetic sensing ability of a carbon microcoil (CMC) with a 3 to 5 µm diameter and 100 to 1000 µm length was evaluated. Since the CMC has an electrically conductive coiled structure, it was found to induce an alternating electromotive force in an alternating magnetic field, similar to a solenoid coil. The electromotive force of the CMC in an alternating magnetic field has a linear relationship with the frequency of the alternating current supplied to an electromagnet. The value of the electromotive force depends on both the number of windings and the electric resistance of the CMC. When a CMC was rotated in a static magnetic field, the electromotive force generated was also related to the frequency of rotation. From these linear relationships, it appears that the CMC could possibly be used as a magnetic micro coil.

Leakage Current Properties of Cation-Substituted BiFeO3Ceramics

Cation-doped BiFeO3 ceramics were fabricated by sintering coprecipitated and calcined powders at 700–900 °C to study the effect of cation doping on the leakage current properties of the sintered samples. Among the dopants examined in this study, Ti4+, Sn4+, or Zr4+ doping was found to effectively reduce the leakage current of the samples. In particular, a marked decrease in the leakage current density was achieved at 10% Ti4+ doping, which also resulted in the structure change from rhombohedral to cubic. The codoping of Ti4+/Zn2+ ions or Ti4+/Ni2+ ions brought about a substantial reduction in the leakage current density of the bulk samples by about four or five orders of magnitude at a small doping amount of 2%. This can be explained by the combined effect of Ti4+ doping, which basically contributes to the decreased number of oxygen vacancies in the sample, and Zn2+ or Ni2+ doping, which might assist the homogeneous substitution of Ti4+ ions for the Fe3+ sites.

Microwave and magneto-optic properties of pulsed laser deposited bismuth iron garnet films

We report on processing and comparative characterization of epitaxial Bi/sub 3/Fe/sub 5/O/sub 12/ (BIG) films grown by pulsed laser ablation of a precursor oxide target onto (NdGd)/sub 3/(ScGa)/sub 5/O/sub 12/ [NGSGG[111]] and Gd/sub 3/(ScGa)/sub 5/O/sub 12/ [GSGG[001]] single crystals. Comprehensive X-ray diffraction analyses reveal the epitaxial quality of the BIG films: they are single phase, exclusively [111] and [001] oriented with less than 0.4/spl deg/ and 0.06/spl deg/ of the full width at half maximum of the rocking curve of main texture Bragg reflection [[111] for NGSGG and [001] for GSGC substrate, respectively]. The films are strongly in-plane textured with cube-on-cube film-to-substrate epitaxial relationship. VSM and ferromagnetic resonance measurements revealed in-plane magnetization in BIG/GSCG[001] film, while the BIG/NGSGG[111] film was found to have perpendicular magnetization. For BIG[001] and [111] films the saturation magnetization 4/spl pi/M/sub s/ was found to be 1400 and 1200 Gs; the Faraday rotation at 635 nm was -7.8 and -6.7 deg//spl mu/m; the constant of uniaxial magnetic anisotropy was K/sub u/*=-8.70/spl times/10/sup 4/ and +1.16/spl times/10/sup 4/ erg/cm/sup 3/; the constant of cubic magnetic anisotropy K/sub 1/=-3.6/spl times/10/sup 3/ and -7.14/spl times/10/sup 3/ erg/cm/sup 3/. High Faraday rotation and low coercive field (/spl les/40 Oe) of BIG/GSGG[001] films show promise for their use in integrated magneto-optic applications.

Nd–Fe–B Thin Films with Perpendicular Magnetic Anisotropy and High Coercivity Prepared by Pulsed Laser Annealing

Amorphous, as-deposited Nd–Fe–B films prepared by RF-sputtering were annealed by irradiating pulsed KrF excimer laser (248 nm). A pulse of 20 ns in width and 4 kJ/m2 in power density was irradiated onto a 2 µm-thick as-deposited film kept at 400°C. It is observed that, by a single shot of the pulse, Nd2Fe14B Φ phase crystallized with prominent texturing of c-axis along the film normal. Annealed films showed excellent magnetic characteristics; Ms=0.978 T, Mr=0.906 T, iHc=1272 kA/m, and (BH)MAX=161 kJ/m3. This process is also found to be successfully applicable to a 20 µm-thick film. Using 2 µm-thick as-deposited film kept at 400°C, micro-magnet patterns of 100 µm in width and 1–2 mm in length were fabricated by irradiating a 20-ns pulse shot through a patterned mask. The patterned area revealed that magnetizations are directed along the film normal with coercivity higher than 1200 kA/m.

Magnetic properties of single crystal film Bi3Fe5O12 prepared onto Sm3(Sc, Ga)5O12(111)

Magnetic properties of single crystal Bi3Fe5O12 has been investigated in the temperature range between 2 and 670K. The Sm3(Sc,Ga)5O12 wafer has been used for substrates. Due to the small contributi ...

Synthesis of Bi-Lu-substituted iron garnet films for visualization of magnetic flux in High-Tc superconductors

In order to visualize the magnetic flux that penetrates into high-Tc superconductors with high spatial resolution, epitaxial growth of the in-plane magnetic Bi–Lu-substituted iron garnet films was investigated. The ratio of increments of Faraday rotation to magnetic field increased to -13 deg/(cmOe) by Bi and Ga substitutions. The as-grown films showed a perpendicular magnetic anisotropy. The appropriate conditions for annealing treatments that change the perpendicular magnetic anisotropy into an in-plane magnetic anisotropy were investigated. Then, the annealed (BiLu)3(FeGa)5O12 film clearly showed a high resolution image of the magnetic flux that penetrates into the NdBa2Cu3O7-δ high-Tc superconductor at temperatures between 5 K and 100 K, and the behavior of the magnetic flux penetrating the microcracks less than 5 µm in width was successfully captured; the magnetic flux depends on external magnetic field and temperature.

Magnetic and magnetooptic properties of LPE films of Nd-Lu-Y iron garnet

Abstract The effects of Nd 3+ and Lu 3+ ions in garnet LPE films are investigated on magnetic and magnetooptic properties. The magnetization and FMR measurements show in-plane anisotropy for both films. Faraday rotation is remarkably enhanced as the content of Nd 3+ ions increases. The anisotropy and Faraday rotation of LuNd-IG film are slightly larger than those of YNd-IG one. This suggests the difference of Nd-segregation coefficient between both systems.

Thermal Expansion of NaZr2(PO4)3 Family Ceramics in a Low-Temperature Range

NZP family ceramics – NaZr2(PO4)3 (NZP), KZr2(PO4)3, RbZr2(PO4)3, Cs Zr2(PO4)3, CaZr4(PO4)6, SrZr4(PO4)6 (SrZP), and BaZr4(PO4)6 – were synthesized by a solid-state reaction, and their thermal expansion properties were investigated by X-ray diffraction measurement in a temperature range of -150 to 250 °C. The increases in the average thermal expansion coefficients of all the NZP family ceramics in this low temperature range (-150 to 250 °C) were smaller than those in a high temperature range (room temperature to 1000 °C). The thermal expansion coefficient of the SrZP ceramic was 0.2×10-6/°C between -150 to 250 °C, which is very small. This proved that SrZP has a near-zero thermal expansion coefficient in a low-temperature range.