Motofumi Homma

M-type ferrite composite as a microwave absorber with wide bandwidth in the GHz range

The electromagnetic wave absorption properties of Ba M-type (BaFe/sub 12-x/(Ti/sub 0.5/Mn/sub 0.5/)/sub x/O/sub 19/) ferrite-epoxy resin composites were investigated. After measuring the complex permittivities of the samples, the regions of complex permeabilities in which the reflection loss (R.L.) becomes less than -20 dB (-20 dB Regions), were calculated. Altering the conditions such as sintering temperature, particle size and the ratio of ferrite powder in the composite samples, resulted in frequency dependencies of permeabilities that agree well with the calculated -20 dB regions, and which lead to an expansion in bandwidth (frequency range (/spl Delta/f) of R.L. <-20 dB). The BaFe/sub 9/(Ti/sub 0.5/Mn/sub 0.5/)/sub 3/O/sub 19/ ferrite-resin composite, which was produced by sintering at 1573 K for 20 h, crushing into powder (150-300 /spl mu/m) and mixing with epoxy resin at a ratio of 70 mass%, exhibited a wide bandwidth (/spl Delta/f=7.2 GHz) from 13.75 GHz to 20.95 GHz. /spl Delta/f values of 1.4-5.4 GHz in the frequency range 6.35-15.65 GHz, were obtained by changing the composition of the BaFe/sub 12-x/(Ti/sub 0.5/Mn/sub 0.5/)/sub x/O/sub 19//epoxy resin composite from x=3.5 to 4.5.

Perpendicular Magnetization of Epitaxial FePt(001) Thin Films with High Squareness and High Coercive Force

Perpendicular magnetized epitaxial FePt(001) thin films were prepared by RF-magnetron sputtering. The long range order parameter S of the FePt layer was found to be ~0.9. Very narrow X-ray rocking curves ( FWHM<1°) of the FePt(002) and Pt(200) peaks indicate that both layers are essentially single crystalline. With increasing Pt buffer layer thickness d Pt, the squareness M r/M S and coercive force H C were found to increase to 100% and 7.2 kOe, respectively. The FePt(001) thin film has a |0.58°| peak at a photon energy of 2.0 eV (630 nm wavelength) in the polar magnetooptical Kerr rotation θ K spectrum, which does not agree with that of the polycrystalline FePt ordered alloy.

Microstructure and magnetic properties of Fe-Cr-Co alloys

The microstructures of an Fe-31wt%Cr-23wt%Co ductile permanent magnet alloy after isothermal aging, thermomagnetic treatment, and step aging have been characterized by transmission electron microscopy and by measurement of the Curie temperature. Isothermal aging itself produces the undesirable microstructure. Aging at 600°C develops the magnetic chromium-rich phase. Aging at 600°C produces a nonmagnetic chromium-rich phase dispersed within the iron-rich phase. The effect of thermomagnetic treatment on the microstructure of the alloy is discussed in comparison with that of Alnico alloys. Step aging produces the deskable microstructure, viz., the elongated ferromagnetic phase imbedded in the paramagnetic phase.

Fe-Cr-Co permanent magnet alloys containing Nb and Al

The vertical section of the Fe-Cr-Co system at 15 wt%Co, 1 wt%Nb and 1 wt%Al was constructed. The extention of the α phase region of the system was sufficient enough to allow for the solution treatment of the alloys at 25∼30 wt%Cr content at any temperature above the α 1 +α 2 miscibility gap. After step-tempering, their magnetic properties were given as Br = 11.5∼13 KG, Hc = 500∼600 Oe and (BH)max = 4∼5 MGOe. These values were also achieved by continuous cooling from α phase region. The addition of Nb and Al to Fe-Cr-Co system will facilitate a practical manufacturing for producing Fe-Cr-Co permanent magnets.

Phase diagram of Fe-Cr-Co permanent magnet system

The miscibility gap of the α phase in Fe-Cr-Co permanent magnet alloys is constructed using mechanical hardness and Curie temperature measurements. It is found that the miscibility gap of the Fe-Cr binary system develops into Fe-Cr-Co ternary system, and that the addition of cobalt raises the decomposition temperature, and extends the difference in concentrations between the iron rich phase (α 1 ) and the chromium rich phase (α 2 ). For instance, the α phase of an Fe-31%Cr-23%Co alloy exhibits a miscibility gap below 670°C, and decomposes into the (α 1 ) phase of 65%Fe-32%Co-3%Cr and the (α 2 ) phase of 69%Cr-21%Fe-10%Co at 600°C.

Effect of V and V + Ti additions on the structure and properties of Fe-Cr-Co ductile magnet alloys

The vertical sections of the Fe-Cr-Co system at 15wt%Co + 3wt%V, at 15wt%Co + 5wt%V, and at 15wt%Co + 3wt%V + 2wt%Ti are constructed. The extension of the α phase region of the system at 15%Co and 5%V, and at 15%Co and 3%V + 2%Ti is enough to allow for the solution treatment of the alloys with 21∼23%Cr at any temperature above the \alpha_{1}+\alpha_{2} miscibility gap. After step-tempering, their magnetic properties are given as Br=13.5 KG (1.35T), Hc=550 Oe (44kA/m) and (BH)max=5.5 MGOe (44kJ/m3). The addition of V or V + Ti to the Fe-Cr-Co system can facilitate the practical manufacture of permanent magnets.

Magnetic microcapsules for targeted delivery of anticancer drugs

To achieve targeted distribution of anticancer drugs with sustained activity, ferromagnetic ethylcellulose microcapsules containing an anticancer drug, mitomycin C (FM-MMC-mc), were prepared by a method based on phase separation principles. Two prototypes of FM-MMC-mc were made: one with the drug as the core and zinc ferrite on its capsular surface (outer type); the other with both the drug and zinc ferrite as the core (inner type). Both preparations provided a sustained-release property and a sensitive response to conventional magnetic force, although certain differences in the release rate of drug, magnetic responsiveness, and particle size were found between the two dosage forms. Animal studies showed that the magnetic microcapsules could be magnetically controlled in the artery and urinary bladder. VX2 tumors in the rabbit hind limb and urinary bladder were successfully treated with magnetic control of FM-MMC-mc. Pharmacokinetic study revealed that the targeting of the microcapsules markedly enhanced the drug absorption into the surrounding tissues for a prolonged period of time. The results indicate the feasibility and effectiveness of the magnetic microcapsules as a targeted drug delivery system.

Microstructure and magnetic properties of Fe‐Cr‐Co‐V alloys

The relationship between the microstructure and magnetic properties of heat treated Fe–23 wt%Cr–15 wt% Co–5 wt%V has been studied by transmission electron microscopy and Lorentz microscopy. Three different heat treatments were adopted for the present investigations, viz., (1) isothermal aging, (2) thermomagnetic treatment (TMT) + step‐aging, (3) continuous cooling. It has been found that the magnetic properties of the alloy are very sensitive to the temperature of the TMT. Step‐aging gave the best magnetic properties, producing an elongated ferromagnetic phase, 300 A in diameter and 1200 A in length. Lorentz microscopy revealed domain walls and these lie within the Cr‐rich phase and pinned by the Fe‐rich phase in the isothermally aged alloy at 650 °C. Magnetic domains of optimally step‐aged alloys, 0.5 μm in width, are elongated along the direction of the applied magnetic field. The results suggest that the magnetic anistropy is introduced parallel to the direction of the applied magnetic field during TMT...

Effects of additives on hydrogenation, disproportionation, desorption and recombination phenomena in Nd2Fe14B compounds

Hydrogenation, desorption, disproportionation and recombination (HDDR) phenomena are very attractive for the production of anisotropic Nd-Fe-B powders with high coercivity. HDDR phenomena are closely related to the characteristics of hydrogen absorption and desorption which correspond to the disproportionation and recombination reactions respectively. The effects of additional elements on these characteristics have been studied. According to the results for Nd 12.6 Fe 81.4 B 6.0 alloys, Nd 2 Fe 14 B compounds disproportionate into a mixture of NdH 2 , α-Fe and Fe 2 B phases at around 650 °C, which recombine to give the original compound at around 1050 °C under atmospheric pressure of hydrogen. The Nd 2 Fe 14 B compound exhibits two hydrogen desorption peaks corresponding to the recombination reaction. Judging from this result, it is considered that the recombination reaction occurs by a two-stage process. The temperature of the hydrogen absorption peak corresponding to the disproportionation reaction shifts to a higher value on the addition of Zr. Alloys with Co or Ga added show lower optimum temperatures of the recombination reaction than those of the alloy without additional elements. It can be said that Zr addition makes the disproportionation reaction sluggish, and Co or Ga addition enhances the recombination reaction in HDDR phenomena.

Fe‐Cr‐Co ductile magnet with (BH)max?8 MGOe

A single crystal of an Fe‐30wt%Cr‐23wt%Co−1wt%Si alloy was prepared by a recrystallization process.The magnetic properties of <100≳, <110≳ and <111≳ single crystals were measured after the following heat treatment. The crystals were solution‐treated at 1300°C for 30 min and then quenched into water. They were tempered in a magnetic field of 2 KOe at 640°C, and were swaged. They were then step‐ tempered. It was found that the best magnetic properties were obtained with the <100< single crystal and were given as Br=13 KG, bHc=980 Oe and (BH)Max=8 MGOe.