Tomohiro Suetsuna

Fabrication of nanocomposite using self-forming core/shell nanoparticles and its magnetic properties at up to gigahertz bands for high-frequency applications

A nanocomposite with a magnetic loss factor (tan δ=μ″/μ′) of less than 1% at up to 1 GHz was synthesized using self-forming core/shell nanoparticles of metal/oxide; these were concentrated to achieve a relative permeability (μ′) of more than three. The self-forming core/shell nanoparticles were synthesized by oxidation of a portion of FeCoAl nanoparticles in thermal plasma. An FeCoAl complex oxide shell of approximately 2 nm in thickness was formed on the surface of FeCo nanoparticle, which had approximately 20 nm in diameter. The core/shell nanoparticles were mixed with resin to form bulk material of millimeter-order thickness.

Bulk nanocomposite using self-forming core/shell nanoparticles and its magnetic properties for high-frequency applications

A bulk nanocomposite composed of tightly packed self-forming core/shell nanoparticles of metal/oxide was fabricated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition were controlled in the nanocomposite, and their effects on the magnetic properties were investigated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor at GHz bands. High permeability with a low loss factor of less than 1.5% at up to 1 GHz was obtained in the nanocomposite in which the nanoparticles with a crystalline grain size of approximately 15 nm were tightly packed.

High-frequency magnetic properties of (FeCoNbB)-(SiO2) nanocolumnar films

(FeCo)-(SiO2) nanogranular films in which magnetic metal particles form nanosized columns, nanocolumnar, were studied. The nanostructure was formed by controlling the composition ratio of magnetic metal and insulating oxide. Inducing uniaxial anisotropy in the film plane resulted in high permeability in the GHz band and a high ferromagnetic resonance frequency. To improve the permeability loss factor, crystallinity of FeCo was controlled by adding B and Nb. As a result, an amorphous nanocolumnar film with ferromagnetic resonance frequency of greater than 5 GHz, high relative permeability of 44.9, and low loss factors of less than 1% up to 1 GHz was achieved.