Shin Noguchi

Magnetoresistance and preferred orientation in Fe-Mn/Ni-Fe/Cu/Ni-Fe sandwiches with various buffer layer materials

Magnetoresistance effects and film structures have been investigated in [Fe–Mn/Ni–Fe/Cu/Ni–Fe/buffer layer/Si] sandwiches with various buffer layer materials. The sandwich with Nb, Ta, Ti, Zr or Hf buffer layer has strong (111) texture. Cu, Ag, Au and Cr buffer layers do not cause strong (111) texture. When the sandwich has strong (111) texture, the Ni–Fe layer neighboring the Fe–Mn antiferromagnetic layer is strongly exchange-biased by the Fe–Mn layer, and thus the sandwich shows a high magnetoresistance ratio.

Performance of Z-type hexagonal ferrite core under demagnetizing and external static fields

The effects of a demagnetizing field and an external static magnetic field on the effective Snoek’s product of textured Z-type hexagonal ferrite, which is the product of effective susceptibility and resonance frequency, were examined in order to apply the Z-type hexagonal ferrite to high-frequency devices. As a result, the demagnetizing field due to the thin plate geometry increased the resonance frequency and the effective Snoek’s product when a high-frequency magnetic field was applied parallel to the c-plane of the Z-type hexagonal ferrite. Moreover, the resonance frequency, effective susceptibility, and effective Snoek’s product of 7.7 GHz, 10.7, and 82.2 GHz, respectively, were obtained when an external magnetic field that was sufficient to saturate the Z-type hexagonal ferrite slab was applied parallel to the c-plane and perpendicular to the high-frequency magnetic field. Furthermore, the Landau–Lifshitz equation suggested that a large Snoek’s product of over 50 GHz could be obtained with an externa...

Magnetoresistance and Interlayer Exchange Coupling between Magnetic Layers in Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co Multilayers

Magnetoresistance effects and interlayer exchange coupling between magnetic layers have been investigated in [Hf/Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co/Hf] multilayers by varying the thicknesses of the Ni–Fe–Co, Fe–Mn, and Cu layers. When the Fe–Mn layer is thicker than 5.0 nm, it applies a strong exchange-bias field to the neighboring Ni–Fe–Co layer. The multilayers show high magnetoresistance ratios at Cu-layer thicknesses between 2.0 and 3.0 nm, because the interlayer exchange coupling is weak. The interlayer exchange coupling between the two Ni–Fe–Co layers is always ferromagnetic at Cu-layer thicknesses between 0.5 and 5.0 nm.

Novel Method for Evaluating Frequency Response of Permeabilities in the c-Plane and Along the c-Axis of Z-Type Hexagonal Ferrite

In this study, a novel method was developed to evaluate the permeability along a certain direction (directional permeability) in the high-frequency range. Two kinds of polycrystalline textured Z-type hexagonal ferrites whose easy planes of magnetization lie in a certain plane and in a certain direction were prepared by molding under a magnetic field; these ferrites were used in this method. The permeabilities that were measured from three toroids cut from these textured ferrites were converted to directional permeabilities by examining the relationship between the permeability measured from the toroid and directional permeability. It was noted that the highest directional permeability of over 50 was obtained along the c-plane below 300 MHz, whereas negative permeability values were observed from 1.2 to 10 GHz. On the other hand, the lowest directional permeability of 4 was obtained along the direction that is normal to the c-plane. These results can be made use of designing various inductive devices.

Multi-domain resonance in textured Z-type hexagonal ferrite

The resonance frequency of a non-saturated Z-type hexagonal ferrite under a demagnetizing field effect was formulated. The permeabilities along the c-axis and the c-plane were measured by a specimen cut from the c-plane-textured Z-type ferrite, and the resonance frequency was measured as a μ″ peak. The resonance frequency measured from the permeability in the c-plane increases dramatically as the specimen’s thickness increases. On the other hand, the resonance frequency measured from the permeability along the c-axis remains fairly constant. We tried to analyze the reason for the large difference in the resonance frequency depending on the crystal orientation using multi-domain resonance theory. As a result, the resonance frequency of a textured Z-type ferrite has been expressed when the high frequency magnetic field is parallel and normal to the c-plane. Therefore, it is confirmed that a demagnetizing field increases the resonance frequency, especially when the high frequency magnetic field is parallel t...

Magnetoresistance effects in spin-valve multilayers including three Ni-Fe-Co layers

Magnetoresistance effects have been investigated in spin-valve multilayers including three Ni–Fe–Co layers. The layered structure of the spin-valve multilayers are [AF1/Ni–Fe–Co/Cu/Ni–Fe–Co/Cu/Ni–Fe–Co/AF2/Si], where AF1 and AF2 are antiferromagnetic layers. The spin-valve multilayers including three Ni–Fe–Co layers show magneto-resistance ratios Δρ/ρ of 3.7% and 5.6% at around 1.5 kA/m. These values are higher than the 2.2% of a spin-valve sandwich that includes two Ni–Fe–Co layers, [Ni–Fe–Co/Cu/Ni–Fe–Co/Fe–Mn/Cu/Hf/Si]. It is found that the total resistivity changes (Δρ) of the spin-valve multilayers including three Ni–Fe–Co layers are twice that for the spin-valve sandwich that includes two Ni–Fe–Co layers. This is due to the fact that the number of Ni–Fe–Co/Cu interfaces in the spin-valve multilayers that include three Ni–Fe–Co layers is double that in the spin-valve sandwich that includes two Ni–Fe–Co layers.

Magnetoresistance Effects of Fe-Mn/Ni-Fe-Co/(Au, Ag, Al)/Ni-Fe-Co Sandwiches

Magnetoresistance effects and film structures have been investigated in [Hf/Fe-Mn/Ni-Fe-Co/(Au, Ag, Al)/Ni-Fe-Co/Hf/Si] sandwiches. The sandwiches show high magnetoresistance ratios when the Au and Ag spacers are thicker than 2.0 and 4.0 nm, respectively. The resistivity changes are almost equal to those of [Hf/Fe-Mn/Ni-Fe-Co/Cu/Ni-Fe-Co/Hf/Si] sandwiches. The sandwiches with Al spacers show magnetoresistance ratios of almost 0%, although the configuration of magnetisations of the two Ni-Fe-Co layers changes between parallel and antiparallel. Each sandwich has a strong (111) texture. The thickness of the Ag spacer is not homogeneous. The sandwiches show about the same thermal stabilities, whether the nonmagnetic spacer is Cu, Ag or Au.

Interlayer couplings and magnetoresistance effects of Fe/Cr/Fe/Ni-Fe/NiO sandwiches

Interlayer coupling between Fe layers and magnetoresistance effect have been investigated in Fe/Cr/Fe/Ni-Fe/NiO sandwiches. The interlayer coupling between two Fe layers oscillates as the thickness of Cr layer changes. The strongest antiferromagnetic coupling is observed when the thickness of the Cr layer is 1.2 nm. The highest magnetoresistance ratio due to spin-dependent scattering is only 0.13%. The low magnetoresistance ratio is thought to be caused by high resistivity of the Cr layer.