Yoshikazu Narumiya

Giant Magnetoresistance and Oscillatory Magnetic Coupling of Evaporated and MBE-Grown Co/Ag Multilayers

Co/Ag multilayers grown by molecular beam epitaxy (MBE) exhibit giant magnetoresistance (MR). The spins of Co layers are aligned antiferromagnetically, which is the same as in Fe/Cr and Co/Cu. The MR ratio and saturation field showed oscillatory behavior as a function of Ag thickness with a period of about 16 A. The MR ratio was obtained for [Co(6 A)-Ag(25 A)]×70, 16% at room temperature and 38% at 77 K.

Soft Magnetic Properties of Electrodeposited CoNiFe Films

The soft magnetic properties of electrodeposited CoNiFe films were studied. Films composed of 30 to 50 wt% Co, 23 to 35 wt% Ni and 25 to 35 wt% Fe alloy with a high saturation flux density of more than 1.5 T exhibit low coercivities under 0.2 Oe. Film composed of 40 Co-30 Ni-30 Fe alloy, consisting primarily of an fcc phase with some bec phase material and created by annealing at 300°C, has excellent soft magnetic properties (Hc=0.06 Oe, ¿=3200, Bs=1.8 T). This bcc phase makes an appearance during the first stage of crystallization at 287°C. The structure is thermally unstable, and is due to a special feature of electrodeposition. During the annealing, H2O, H2 and CO2 were released from the film, but the patterns of generation of these gases bear little relation to the DSC pattern.

Linearity and hysteresis in the magnetoresistive response of (NiFe,NiFeCo)/Cu and Co/Cu/NiFe multilayers in patterned stripes

The linearity and hysteresis in the magnetoresistive (MR) response of NiFe/Cu and NiFeCo/Cu multilayers prepared by ion beam sputtering, and Cu/Co/Cu/NiFe multilayers prepared by MBE are investigated. These characteristics in the linear regions for the second peak of antiferromagnetically coupled NiFe/Cu multilayers are almost the same as those of NiFeCo/Cu ones at 50‐Hz ac applied fields. The MR amplitude at the first peak is inferior to that at the second one, whereas, the linearity and hysteresis are superior. In weakly coupled Cu/Co/Cu/NiFe multilayers, a nonhysteretic MR response is obtained at a NiFe layer thickness of 10 A. The linearity and symmetry around the zero magnetic field of the MR curve depend on the Cu layer thickness. When the thicknesses of the NiFe and Cu layers are 10 and 45 A, respectively, good linearity and no hysteresis are observed without biasing techniques. The output levels in the linear regions of three different multilayers are 1.5–2.5 times as large as that of the conventi...

Effects of Cr Addition into Fe-Cu-Nb-Si-B Alloys

The effects of Cr addition on the soft magnetic properties and chemical characteristics of nanocrystalline Fe-Cu-Nb-Si-B alloys were studied. Corrosion resistance of nanocrystalline alloys annealed in a nonoxidizing atmosphere is better than that of pre-annealed amorphous alloys. Addition of small amounts of Cr and the use of a nonoxidizing annealing atmosphere are very effective for improving the chemical properties of the nanocrystalline alloys. Fe<inf>72.5</inf>Cr<inf>1</inf>Cu<inf>1</inf>Nb<inf>3</inf>Si<inf>13.5</inf>B<inf>9</inf> alloy exhibits both a high permeability of about 75,000, and excellent corrosion resistance.

Soft Magnetic Properties of Microcrystalline Fe-Al-Si-Ni-Zr-B Alloys

The magnetic properties of Zr- and B-doped Supersendust (Fe-Al-Si-Ni) alloy ribbons were studied. Although the ribbons became brittle and their magnetization decreased with increases in the Zr and B contents, their soft magnetic properties were improved. Ribbons with ductility after melt quenching and fairly low coercivity after annealing were obtained when about 1.5 at% Zr and 8 at% B were added. The structural change from an amorphous to a microcrystal-line state led to a decrease in the magnetostriction and coercivity and an increase in the initial permeability. Microcrystalline Fe69.7Al7Si9.8Ni4Zr1.5B8 alloy exhibited high permeability of about 25,000.

Thermal Stabilities of Cu/Co/Cu/NiFe Multilayers

Cu/Co/Cu/NiFe multilayer films prepared by evaporation deposition in an ultrahigh vacuum were heat-treated in air and in ultrahigh vacuum. Heat treatment in ultra-high vacuum brought about no changes in the MR ratio or MR slope for annealing temperatures less than 400C. The thermal stability in air was limited by gradual oxidation from the surface, and thermal stability up to 250°C was verified. Improved thermal stability was achieved by the use of thicker NiFe layers.

Giant magnetoresistance in induced ferrimagnetic multilayers grown by MBE

Induced ferrimagnetic Cu/(Co,CoNi,CoFe)/Cu/NiFe multilayers were prepared by E-beam evaporation in molecular beam epitaxy system and showed giant magnetoresistance. It is confirmed that weak interlayer magnetic interacuon works between soft and hard magnetic layers. The output voltage was roughly estimated as twice and a half as that of conventional NiFe element in an ac magnetic field of 50 Hz. Thermal stabilities were verified for the Cu/Co/Cu/NiFe multilayers for more than 400 in heat treatment in vacuum and 250°C in air.

Effect of Growth Temperature on Structures and Magnetoresistive Properties of Fe/Cr Multilayers

Fe/Cr multilayer films, [Fe (21Å)-Cr (13Å)]×30, were deposited on MgO (100) single crystal and glass substrates by vacuum evaporation, with the substrate temperature varied. The resistivity under zero field was smallest, and the magnetic contribution was largest, for samples prepared with the substrate temperature between 150°C and 200°C, which accordingly exhibited the largest magnetoresistive change below 3 kOe (6% at room temperature, 20% at 77K).

Investigation on the Lossy Electro-Magnetic Shielding Materials by Ferrite and Resistive Materials

Lossy electro-magnetic shielding materials were investigated to reduce the radiation noise from electronic equipments. Two types of shielding sheets are proposed here and shielding effects are discussed both theoretically and experimentally. These results are very useful for designing the electronic equipments with small radiation noise.