Akimitsu Morisako

The effect of underlayer for Ba-ferrite sputtered films on c-axis orientation

A thin amorphous Ba–Fe–O film was deposited as an underlayer for the growth of c-axis oriented hexagonal barium ferrite (BaM) films using a facing targets sputtering system. This underlayer facilitates the crystallization and improves the crystallinity for hexagonal M phase. BaM films with c-axis orientation can be prepared at Ts of 525 °C on the underlayer. BaM films prepared on this amorphous underlayer exhibit a good c-axis orientation with c-axis dispersion angle Δθ50 as small as 3°. It is shown by the x-ray photoemission spectroscopy profile that this underlayer prevents deep diffusion of Ba and Fe into the substrate surface.

Enhanced magnetic properties of Dy3+ substituted Ni-Cu-Zn ferrite nanoparticles

Dy3+ substituted Ni-Cu-Zn (Ni0.4Cu0.4Zn0.2DyxFe2−xO4) ferrite nanoparticles were obtained at 600 °C by synthesizing sol-gel auto-combustion method, and they exhibit a particle size of 12–21 nm. X‐ray diffraction patterns confirm the presence of secondary phase of DyFeO3 and Fe2O3 for the Dy3+ substituted samples. Ni‐Cu‐Zn ferries doped with Dy3+ possess better grain structure and growth than that of pure Ni‐Cu‐Zn ferrite. The saturation magnetization increases remarkably up to 81 emu/g with increasing the Dy3+ ions. The increased saturation magnetization related to increased exchange interactions between Fe‐Fe ions and also with increased particle size. Blocking temperature was found to decrease with increasing Dy3+ substitution. An enhancement in initial permeability and Curie temperature was observed with Dy3+ substitution.

Microwave Absorption Properties of Mn–Co–Sn Doped Barium Ferrite Nanoparticles

Substituted barium ferrite BaFe₉(Mn_0.5Co_0.5Sn)_3/2O₁₉ was prepared by sol-gel method. X-ray diffraction (XRD), transmission electron microscope (TEM), AC susceptometer, vibrating sample magnetometer (VSM) and vector network analyzer were used to analyze the structure, static and dynamic magnetic properties of the prepared samples. The prepared ferrite particles possess irregular non spherical shape with a broad size distribution. The substitution was very effective in reducing coercive field of the material. Based on microwave measurements of reflectivity, BaFe₉(Mn_0.5Co_0.5Sn)_3/2O₁₉ is a good candidate for electromagnetic compatibility and other practical applications at high frequencies.

Effect of Additional Elements on the Structural Properties, Magnetic Characteristics and Natural Resonance Frequency of Strontium Ferrite Nanoparticles/Polymer Composite

Substituted strontium ferrites SrFe_12-xMg_x/2Sn_x/2O₁₉ (x=1 , 2 and 3) were prepared by sol-gel method. X-ray diffraction (XRD), transmission electron microscope (TEM), AC susceptometer, vibrating sample magnetometer (VSM) and vector network analyzer were used to analyze the structure, static and dynamic magnetic properties of the prepared samples. The prepared ferrite particles possess irregular non spherical shape with a broad size distribution. The substitution was very effective in reducing coercive field. Based on microwave measurements of reflectivity, SrFe_12-xMg_x/2Sn_x/2O₁₉ is a good candidate for electromagnetic compatibility and other practical applications at high frequencies.

Low‐temperature deposition of hexagonal ferrite films by sputtering

Pb‐substituted Ba‐ferrite films were prepared at various substrate temperature Ts by dc magnetron sputtering and their crystallographic characteristics and magnetic properties were investigated. The substitution of Pb facilitates the crystallization and improves the crystallinity for hexagonal M phase. All of the films prepared at Ts above 460 °C exhibit a good c‐axis orientation and the c‐axis dispersion angle (Δθ50) for Pb‐substituted Ba‐ferrite films is as small as 1°. The coercivities (Hc⊥) and Hc∥) and saturation magnetization Ms of Pb‐substituted Ba‐ferrite films are 0.7–1.0 kOe, 0.2 kOe and 250–300 emu/cm3, respectively.

Switching of magnetic easy-axis using crystal orientation for large perpendicular coercivity in CoFe2O4 thin film

Perpendicular magnetization and precise control over the magnetic easy axis in magnetic thin film is necessary for a variety of applications, particularly in magnetic recording media. A strong (111) orientation is successfully achieved in the CoFe2O4 (CFO) thin film at relatively low substrate temperature of 100 °C, whereas the (311)-preferred randomly oriented CFO is prepared at room temperature by the DC magnetron sputtering technique. The oxygen-deficient porous CFO film after post-annealing gives rise to compressive strain perpendicular to the film surface, which induces large perpendicular coercivity. We observe the coercivity of 11.3 kOe in the 40-nm CFO thin film, which is the highest perpendicular coercivity ever achieved on an amorphous SiO2/Si substrate. The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime. Importantly, this can be achieved on virtually any type of substrate.

Enhanced reflection loss characteristics of substituted barium ferrite/functionalized multi-walled carbon nanotube nanocomposites

In this research work, magnetic multi-walled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mn-Co-Ti-substituted barium ferrite nanoparticles onto the surface of MWCNTs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to demonstrate the successful attachment of ferrite nanoparticles to MWCNTs. Vibrating sample magnetometry (VSM) confirmed the relatively strong dependence of saturation magnetization on the volume percentage of MWCNTs. Microwave absorption of the MWCNTs/doped barium ferrite (BaM) nanocomposites is evidently enhanced compared to that of pure MWCNTs and ferrite nanoparticles. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs in nanocomposites.

A comparison between magnetic and reflection loss characteristics of substituted strontium ferrite and nanocomposites of ferrite/carbon nanotubes

Large-scale carbon nanotubes (CNTs)/substituted strontium ferrite nanocomposites have been fabricated by hetero-coagulation. The structure and morphology of nanoparticles and nanocomposites were evaluated by high-resolution transmission electron microscopy (HRTEM). HRTEM confirmed that strontium ferrite was successfully attached to carbon nanotubes. The vibrating sample magnetometer (VSM) confirmed the relatively strong dependence of saturation magnetization with the volume percentage of multi-walled carbon nanotubes (MWCNTs). Reflection loss of nanocomposites at 12–18 GHz was evidently enhanced, as compared to that of strontium ferrite nanoparticles. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs. It was proved that the microwave absorbing bandwidth was modulated simply by manipulating the thickness of nanocomposites. Reflection loss evaluations indicate that the nanocomposites display a great potential application as wide-band electromagnetic wave abs...

Magnetic anisotropy and soft magnetism of iron nitride thin films prepared by facing‐target sputtering

Iron nitride thin films have been prepared at various nitrogen‐gas pressures (PN2) on a heated substrate by using a facing‐target sputtering (FTS) system, and their crystallographic characteristics and magnetic properties have been investigated. Total gas pressure (PN2+PAr) was set at 2 mTorr. MS for the films prepared at PN2 below 0.05 mTorr was slightly higher than 1700 emu/cc with scattering and did not show apparent dependence on PN2. These films exhibited a bcc structure, and the lattice constant was about 2.875 A, which was larger than that of bulk iron. Large values of compressive stress were observed in these films. The films prepared with pure argon gas exhibited isotropic magnetic properties in the film plane, while the films with PN2 above 0.07 mTorr exhibited magnetic anisotropy in the film plane. The direction of the easy axis was parallel to the magnetic stray field in the FTS system. The films with soft magnetism were prepared at PN2 around 0.1 mTorr, which corresponded to the onset of the ...

SmCo/Cr bilayer films for high-density recording media

The magnetic properties of a SmCo layer on a Cr underlayer, which was prepared by various Ar gas pressure (PAr), were studied. A single line appeared in each X-ray diffraction diagram and its intensity became strong when PAr was decreased from 1.06 to 0.13 Pa. The microstructure observed by using atomic force microscopy showed that the surface morphological structure of Cr underlayers depended on PAr and the surface of the Cr underlayer became smoother as PAr was decreased, while the surface and the grain of the SmCo layer on the Cr underlayer were independent of PAr. The grain size of SmCo layers was as small as 30 nm with the surface roughness of about 1 nm. The coercivity, the squareness ratio, and the coercivity squareness ratio of the SmCo layer on the Cr underlayer prepared at 0.13 Pa were 155 kA/m, 0.92 and 0.92, respectively. Those values suggest that an easy axis of magnetization for the SmCo layer is in plane and the switching field distribution is very small. Although the crystal structure of t...