Fumitoshi Yamashita

Fabrication of Nd-Fe-B thick-film magnets by high-speed PLD method

In this paper, the targets with the compositions of Nd/sub x/Fe/sub 14/B (X=2.0-4.0) were prepared. Then, they were ablated with a pulse laser at the repetition rate of 30 Hz, and films were deposited on Ta substrates. The coercivity and remanence of the films were almost independent of the film thickness at approximately 1000 kA/m and 0.55 T within the thickness range of 10-80 /spl mu/m. Also the maximum energy product value of 77 kJ/m/sup 3/ as the best magnetic property was obtained by using the high speed PLD method.

Review of Fabrication and Characterization of Nd–Fe–B Thick Films for Magnetic Micromachines

Isotropic Nd-Fe-B thick film magnets were prepared by a high-speed pulsed laser deposition method followed by a post annealing. The deposition rate of 90 mum/h could be successfully achieved, and a pulse annealing was adopted as the post annealing process in order to enhance coercivity. Use of a substrate heating system under the high deposition rate enabled us to obtain anisotropic thick films with (BH) max of approximately 120 kJ/m3, which show the potential for an improvement in the properties of the micromachines. Novel micromachines comprising the isotropic films were introduced

New method of making Nd-Fe-Co-B full dense magnet

A novel method for fabricating an isotropic fully dense Nd-Fe-Co-B magnet is described. This method consists of a plasma-activating process and a hot-pressing process. The magnetic powder is heated by resistance heating. Plasma activation produces an improvement in the H/sub cj/ of the compacted magnet. The pressure range is from greater than 200 kg/cm/sup 2/ to less than 500 kg/cm/sup 2/. Optimum alloy composition is Nd/sub 13.5/Co/sub 1.5/B/sub 6/Fe/sub 64.5/, specified by magnetic properties and formability in hot pressing. The magnetic properties of this magnet are 15 MG-Oe for BH/sub max/ and 17 kOe for H/sub cj/. The temperature coefficient of B/sub r/ is -0.07 to -0.08%/ degrees C, and that of H/sub cj/ is -0.39 to -0.42%/ degrees C. >

Enhancement in magnetic torque of cylindrical micro rotor by usage of directly consolidated α-Fe/Pr2Fe14B-based nanocomposite thick-films

An advanced preparation method was carried out to obtain a magnetized cylindrical micro rotorfabricated from directly consolidated isotropic α-Fe/Pr2Fe14B nanocomposite thick-films with self-bonding layer. A magnetic torque of the above film with the remanence value of 0.97 T, the coercivity value of 650 kA/m, and the (BH)max value of 142 kJ/m3 was investigated under different field strengths. Namely, magnetic torque of the above-mentioned rotor with a single pole pairincreased by 117%, compared with that of Fe3B/Nd2Fe14B films with the remanence value of 1.1 T, the coercivity value of 334 kA/m, and the (BH)max value of 95 kJ/m3. It was found that the use of α-Fe/Pr2Fe14B films is effective in obtaining a multipolarly magnetized micro rotor with highly dense torque as well as magnetic stability.

Effect of laser beam parameters on magnetic properties of Nd–Fe–B thick-film magnets fabricated by pulsed laser deposition

The effects of varying the laser power and the spot diameter of a laser beam on the magnetic properties, morphology, and deposition rate of Nd–Fe–B thick-film magnets fabricated by pulsed laser deposition (PLD) were investigated. Reducing the laser fluence on the target reduces the remanence and increases the Nd content and consequently the coercivity of the prepared films. The spot size of the laser beam was found to affect the film surface morphology, the deposition rate, and the reproducibility of the magnetic properties of the prepared films. Reducing the spot size reduces the number of droplets and the reproducibility of the magnetic properties and increases the droplet size. Controlling the spot size of the laser beam enabled us to maximize the deposition rate. Consequently, a coercivity of 1210 kA/m and a remanence of 0.51 T were obtained at a deposition rate of 11.8 μm/(h·W). This deposition rate is 30% greater than the highest previously reported deposition rate by PLD.

Enhancement in coercivity of pulse-laser-deposition-made Nd–Fe–B thick film magnets by high-speed crystallization

In order to improve the magnetic properties of Nd–Fe–B thick film magnets prepared by pulsed laser deposition, high-speed crystallization method of a pulse annealing was adopted as a postannealing process. In the case of using a Nd2.4Fe14B target, the pulse annealing under an optimum condition for the period of 1.8s enabled us to enhance the coercivity by approximately 300kA∕m compared with the average value of samples annealed by a conventional method. The obtained sample whose composition was almost as same as the target’s one had the large coercivity of approximately 1300kA∕m, and values of remanence and (BH)max were 0.62T and 64kJ∕m3, respectively. It was also clarified that use of a Nd2.2Fe14B target together with the pulse annealing method is effective to increase remanence and (BH)max although the coercivity value decreased.

Direct joule heating of Nd-Fe-B based melt-spun powder and zinc binder

This contribution reports a newly developed technique to prepare zinc-bonded magnets using granular compounding and direct Joule heating. The authors evaluate the granular compound compactibility and magnetic properties of the prepared magnets, and compare them with those of epoxy-resin bonded magnets.

Prediction method of flux loss in anisotropic NdFeB/SmFeN hybrid magnets

We systematically evaluated the initial flux loss of anisotropic HDDR-NdFeB/RD-SmFeN hybrid bonded magnets. The measured flux loss values were compared with those obtained by two prediction methods based on our previous proposal. Consequently, it was clarified that the initial flux loss of anisotropic bonded magnets can be predicted from demagnetization curves at room and exposure temperatures of the corresponding hybrid magnets, which suggests that the method proposed previously for isotropic magnets can be also applicable to anisotropic ones.

Investigation on Magnetic Torque of Multi-Polarly Micro Rotor Using Shape-Magnetic-Anisotropy

A double pole pair milli-size rotor with 1 mm in outer diameter and 0.3 mm in inner diameter was fabricated from an isotropic laminated film magnet with a non-magnetic material. Permeance coefficient distribution together with static magnetic field of the film were also estimated by using 3-D and 2-D finite element model, and the average permeance coefficient, B/¿oH, could be estimated as 18.7. A torque of the isotropic film magnet with the remanence value of approximately 1 T was measured under the different field strength, and a relative torque and relative torque constant, dT/dH-gradient, of the above-mentioned magnet with the double pole pair increased by 172% and 152%, respectively, compared with those of an anisotropic bulk magnet with a single pole pair whose remanence value was approximately 1.3 T. It was found that use of isotropic laminated film magnet is effective in obtaining a micro multi-polarly magnetized rotor with highly dense torque.

Flux loss in nanocomposite magnets

The irreversible flux loss due to exposure to an elevated temperature was evaluated systematically for nanocomposite magnets with various coercivity values. It was found that the short-term and long-term flux losses in some nanocomposite magnets are smaller than in a conventional isotropic Nd-Fe-B magnet despite their small coercivity values. The origins of the observed small values for flux loss were studied by using the proposed model. It was clarified that the observed small values for the short-term flux loss in the nanocomposite magnets can be attributed to the squareness of a demagnetization curve of the nanocomposite magnets not deteriorating at an elevated temperature. The small values for the irreversible susceptibility of the nanocomposite magnets reasonably explained their small values for long-term flux loss.