Shigeru Tadokoro

Exchange coupling between ferromagnetic fcc Ni81Fe19 and antiferromagnetic bcc CrMnPt films

We studied an antiferromagnetic CrMnPtx [(Cr:Mn≂1:1) in atomic percent] film for an exchange‐biased layer, focusing especially on the relationships between the exchange coupling properties of the CrMnPtx (top)/Ni81Fe19(bottom) films and the character of its CrMnPtx film. The best Pt content to obtain a large exchange coupling of the CrMnPtx film was 5.0–8.0 at. %. Typically, the exchange coupled 50 nm CrMnPt5−8/40 nm Ni81Fe19 films exhibited a relatively large exchange coupling field of ∼22 Oe and a high blocking temperature of ∼380 °C. Besides, the CrMnPt5−8 film deposited on the Ni81Fe19 film had a considerably high resistivity of ∼300–350 μΩ cm. These large exchange coupling and high resistivity values were obtained only when the α‐phase with a disordered bcc structure was stabilized in the CrMnPtx film by the underlying fcc Ni81Fe19 film. The Pt within the CrMnPtx film might localize the Mn magnetic moment. As to why the CrMnPtx film having the Pt content of 5.0–8.0 at. % could give the Ni81Fe19 film ...

Magnetic exchange coupling for bilayered Ni81Fe19/NiO and trilayered Ni81Fe19/NiFeNb/NiO films

Exchange coupling between a ferromagnetic film and an antiferromagnetic NiO film was investigated. Bilayered ferromagnetic Ni81Fe19/antiferromagnetic NiO films had a large exchange coupling field and blocking temperature of about 200 °C. In trilayered Ni81Fe19/ferromagnetic (Ni81Fe19)100−xNbx/NiO films, a way could be developed to control the exchange coupling field at a small value by increasing the Nb of the intermediate film. The most important factor in the control seemed to be that the numbers of magnetic Fe and Ni atoms of (Ni81Fe19)100−xNbx, which contributed to the exchange coupling between (Ni81Fe19)100−xNbx and NiO, varied with the existence of nonmagnetic Nb at their interface. From experimental results with other trilayered Ni81Fe19/ferromagnetic (Ni100−xFex)93Nb7/NiO films, it was ascertained that the exchange coupling field seemed to be independent of the magnetic moment of the ferromagnetic film although unidirectional anisotropy constant was proportional to it. As for blocking temperature,...

NIO STRUCTURE-EXCHANGE ANISOTROPY RELATION IN THE NI81FE19/NIO FILMS AND THERMAL STABILITY OF ITS NIO FILM

We studied an antiferromagnetic (AF) NiO film for an exchange‐biased layer, focusing especially on the relationships between the exchange coupling properties of the Ni81Fe19(top)/NiO(bottom) films and the character of its NiO film. Among the variable sputtering conditions, our experimental data showed that the dominant factor determining the exchange coupling properties was the Ar pressure during the NiO film preparation. Better exchange coupling properties resulted when the NiO film was deposited at low Ar pressure which was attributed to: (i) the smooth surface of the NiO film and (ii) the presence of relatively large particle sizes within it. The former was thought to bring about not only an increase in the number of unidirectional exchange coupled Ni81Fe19/NiO spins, but also the appearance of exchange paths having large local exchange anisotropies. The latter was thought to produce an increase in the AF clusters with a particle volume larger than KeiA/KAFi, where Kei, A, and KAFi are local unidirecti...

Structures and Magnetocrystalline Anisotropy of Single Crystal Permalloy Films Deposited by Sputtering Method

Single-crystal permalloy films were grown epitaxially on (001) GaAs substrates by sputtering. The relationship between the crystal orientations of the permalloy and GaAs were (001) NiFe // (001) GaAs, ≪100≫ NiFe // ≪110≫ GaAs. The crystal structures of permalloy films were deformed from cubic to tetragonal; films with positive and negative tetragonal strain have small and large respective unit cell volumes. Films with a small lattice constant in the film plane have a large strain distribution. The magnetocrystalline anisotropy of films with a large strain distribution is small, and that of films with a negative tetragonal strain is large.

Large anisotropic magnetoresistance in ternary NiFeX films for magnetoresistive heads (abstract)

Highly sensitive magnetoresistive heads are required for magnetic disk drives with large areal density. Films with large anisotropic magnetoresistance are among the promising candidates for this purpose. In this work, the effect of third elements, X (Au, Pt, Ag, Cu, Pd, Co, Ru, ZrO2), to Ni80Fe20 alloy on anisotropic magnetoresistivity (Δρ) and other magnetic properties is examined with varying third element composition. Ternary films were deposited by rf sputtering on Ta seed layers. The thicknesses of ternary films were 5–20 nm which were determined by the x-ray reflectivity method. The value of Δρ for ternary films increases when Au, Pt, Ag, Co, and ZrO2 are added. On the other hand, Δρ decreases when Ru is added. Considering the application for the magnetoresistive (MR) head, low ρ0, low Hk, and low Bs are required except for large Δρ. The value of Δρ for Ni74Fe19Au7 film with the thickness of 10 nm is 0.65 μΩ cm which is 20% larger than that for Ni80Fe20. The values of Hk, λ, and Bs for Ni74Fe19Au7 a...