The current status of R&D activities and major results are briefly reviewed, mainly focusing on work reported since about 2010. Developments in and perspectives on less-Dy and Dy-free Nd-(Dy)-Fe-B-type permanent magnets, search and discovery of new hard magnetic materials, progress in the basic understandings of coercivity in hard magnets, and perspectives on anisotropic nanocomposite permanent magnets are overviewed.

抄録全体を表示

  Jitter noise reduction can be achieved by controlling the position of magnetic grains. We have shown that position controlled granular media can suppress jitter noise. In this paper, the influence of grain alignment on square and triangular lattices and the switching field distribution on the jitter noise was calculated with a Voronoi cell model. The switching field distribution was found to have a significant effect and depended on the down-track distance between grains.

抄録全体を表示

  We report the preparation and characterization of bismuth substituted gadolinium iron garnet thin films on (111) gadolinium gallium garnet (GGG) substrates prepared by metal organic decomposition (MOD). Magnetization, Faraday rotation and X-ray diffraction (XRD) were used to examine their dependence on annealing temperatures and different annealing gas mixture (with and without O₂). Our results from measurements revealed that Bi substituted gadolinium iron garnet samples annealed without O₂ (100% N₂) crystallized at lower annealing temperatures. The magnetic fields to saturate the Faraday rotation were larger for the samples annealed without O₂ (100% N₂) than those of samples annealed with 20% O₂. The possible mechanisms responsible for these phenomena are discussed.

抄録全体を表示

  Sub-micron sized magnetic tunnel junctions were fabricated using a dry ice blasting lift-off process for the resist on the magnetic tunnel junction. The fabricated devices showed little difference in transport characteristics from devices made using a conventional chemical lift-off process in an ultrasonic bath sonicator. The distinguished feature of the new process was the achievement of a soft and pure dry ice jet from a well-cooled nozzle with a clear liquid CO₂ flow in a narrow orifice. There was little contamination or damage on the surface of the sample wafer with the pure jet. The dry ice blasting effectively removed the resist for smaller pillar devices with planar sizes of ＜250 nm.

抄録全体を表示

  A highly sensitive probe to measure thin film permeability was developed based on the skin effect. A microstrip-line-type probe on a flexible polyimide substrate was fabricated and placed in contact with a magnetic thin film. The permeability was optimized by the Newton-Raphson method. The permeability of amorphous Co₈₅Nb₁₂Zr₃ film (25 mm x 25 mm and 5 nm in thickness) was evaluated using a permeameter. The measured values were in rough agreement with theoretical values based on the Landau-Lifshitz-Gilbert equation and eddy current generation up to 7 GHz. The proposed method shows promise for the measurement of very thin film (less than 10 nm in thickness) because the contact surface between the flexible probe and thin film fits very well, resulting in improvement of the signal-to-noise ratio.

抄録全体を表示

  The use of short- and open-circuited transmission lines is widely known to be a simple method of measuring the permeability and permittivity of magnetic materials. Lumped element approximation is one of the methods to analyze these transmission lines. However, this approximation generally involves rather large model errors. We describe here a way to reduce these errors. The distributed element expression of short- and open-circuited transmission lines is expanded by a Taylor series, and the first and the second terms are adopted in a limited form. These analyses have clarified that this approximation could hold within ± 5% of model error if a phase shift βl is less than 90% of π/2 (1.4 radian), where β is the propagation constant and l is the sample length.

抄録全体を表示

  Recently, electric vehicles (EVs) have attracted attention as environmental awareness grows. However, current EVs have some problems such as short cruising distance and long charging time; consequently, it is currently difficult for EVs to travel long distances without frequent and long-time charging. This circumstance has stimulated researches into contactless charging systems for moving EVs. These systems can be categorized into two types (segmented coil designs and single-coil designs), and we have been studying single-coil designs as they are superior in system simplicity and equipment costs. However, the coupling between the coils is low in these designs, and consequently, it has been considered to be difficult to efficiently transmit power to an arbitrary load.
  Hence, in this study the LC-Booster method has been applied to such a system in order to overcome the above-mentioned problem. This paper presents the evaluation results at the time of supplying the full-scale Feeding coil with power of approximately 1 kW, and demonstrates that the load can stably receive power even while it is moving on the Feeding coil in the traveling direction, with transmission efficiency of nearly 80%.

抄録全体を表示

To estimate specific power losses (SPL) of bulky magnetic hyperthermia heating mediators, a hysteresis loop measurement system in alternating magnetic field at a constant temperature was fabricated. Magnetic properties of a rectangular sample of La-Sr-Mn-Cu perovskite (LSMC) in a temperature range of 20～46°C were estimated from induced electromotive force which arose in a single turn pickup coil located at the center of exiting coil (1 MHz, 3 kA/m-rms). Complex permeability μ' and μ", coercive force H_c, and SPL of the LSMC decreased with increasing the temperature. Phase delay δ of magnetic flux density of the LSMC from the applied magnetic field were almost the same among measured temperature range.

抄録全体を表示