Akihiko Tsutai

Dual-element GMR/inductive heads for gigabits density recording using CoFe spin-valves

We have succeeded in designing, fabricating, and testing GMR/inductive heads. 1 /spl mu/m trackwidth CoFe spin-valve read elements showed high sensitivity even after head fabrication due to its good thermal stability. About 1.5 /spl mu/m trackwidth a-CoZrNb write elements with Bs (Saturation flux density) of 1.35 T fabricated by trench filling process showed high potential for Gbit density recording. As a result of the feasibility study, 18 kTPI and 140 kBPI are thought to be within the scope by combining the dual element heads with low-noise media.

Structural and magnetic properties of rapidly quenched (R,Zr)(Fe,Co)10Nx (R=Nd,Sm)

The structural and magnetic properties of (R,Zr)(Fe,Co)10(R=Nd,Sm) prepared by the rapid‐quenching method have been investigated. The presence of zirconium makes it possible to realize a TbCu7‐type crystal structure with a high c/a ratio of more than 0.87, while the same crystal structure has a c/a ratio of just 0.84–0.85 in the zirconium‐free case. The saturation magnetization of crystals having such a high c/a ratio as 0.87 exceeds 1.7 T at room temperature. These materials can be nitrogenated, and remarkable enhancement of magnetocrystalline anisotropy by nitrogenation can be seen in the case of Sm. The magnetic hardening of these nitrogenated materials can be achieved by annealing before nitrogenation. The highest value of (BH)max obtained so far for the nitrogenated materials is 144 kJ/m3 (18.0 MGOe). The iHc and Br values for this sample are 503 kA/m (6.3 kOe) and 1.08 T, respectively.

Excellent Reliability Of CoFe-IrMn Spin Valves

The thermal reliability of spin valve films with a CoZrNb/NiFe/CoFe free layer and a CoFe/IrMn pinned layer was investigated. Stable properties; including an MR ratio of 7.5/spl sim/8%, an exchange bias of 400/spl sim/500 Oe in the pinned layer, an interlayer coupling of less than 10 Oe between the pinned and free layers, and soft magnetic properties of the free layer, were observed even after annealing for 100 hours at 270/spl deg/C. It was demonstrated that the IrMn/CoFe interface, as well as the CoFe/Cu interface, is extremely stable against interdiffusion. These films also showed an MR ratio of 5% and an exchange bias of 200 Oe even at 160/spl deg/C.

Effect of Ga addition to NdFeCoB on their magnetic properties

It was found that the Ga addition to NdFeCoB magnets was very effective for improving their magnetic properties. Magnets with high boron concentration had a high coercive force and magnets with low boron concentration had a high‐energy product. The following magnetic properties were obtained: (1) Nd14.5FebalCo16Ga1B9.5:Br=12.0 kG, IHc=15.3 kOe, (BH)max=34 MGOe, Tc=500 °C (2) Nd14.5FebalCo16Ga1B5.5:Br=13.1 kG, IHc=12.2 kOe, (BH)max=40 MGOe, Tc=500 °C. It was also found that NdFeCoGaB magnets with very low boron concentration still had a relatively high coercive force.

A study on the formation of ThMn12 and NaZn13 structures in RFe10Si2

Abstract RFe 10 Si 2 (RLa, Pr, Nd, Sm, Gd, Er and Zr compounds were synthesized by the rapid quench method. The ThMn 12 structure can be obtained in the RFe 10 Si 2 system containing RSm, Gd and Er, while the NaZn 13 structure can be obtained in the system containing RLa, Pr and Nd. It has also been found that Nd 1− x Zr x Fe 10 Si 2 ( x = 0.25, 0.5 and 0.75) crystallized in the ThMn 12 structure. The factors which control the formation of ThMn 12 and NaZn 13 structures in the RFe 10 Si 2 system are discussed with respect to the atomic radius of the rare earth site element.

Magnetic properties and microstructure of rapidly quenched SmZrFeCoN magnets

Dependence of magnetic properties and microstructure on boron additions for nitrogenated (Sm,Zr)(Fe,Co)/sub 9/ alloys fabricated by rapidly quenching was investigated. The condition for getting high (BH)/sub max/ with high /sub i/H/sub c/ is to produce an amorphous phase in the rapidly quenched sample because it leads to the precipitation of uniform and fine grains by the annealing above their crystallization temperature. The role of boron is to form the amorphous phase easily by rapidly quenching. High (BH)/sub max/ of about 20 MGOe with high /sub i/H/sub c/ of 9.6 kOe was obtained for nitrogenated (Sm/sub 0.7/Zr/sub 0.3/)(Fe/sub 0.95/Co/sub 0.05/)/sub 9/B/sub 0.1/. High (BH)/sub max/ of 13.0 MGOe was also attained as an isotropic resin bonded magnet with density of 6.2 g/cm/sup 3/.

Coercive force of Co added Nd-Fe-B based powders prepared by crushing sintered magnets

An anisotropic resin-bonded magnet was prepared by crushing sintered Nd-Fe-B magnets with Co-Al or Co-Ga. The following magnetic properties for the composition of Nd/sub 14.5/Fe/sub 63/Co/sub 16/Ga/sub 1/B/sub 5.5/ were obtained: (BH)/sub max/=114 kJ/m/sup 3/, B/sub r/=0.89 T, and iH/sub c/=810 kA/m. Co addition is shown to play a significant role in improving the magnetic properties of the crushed powder. The surface layer damaged by crushing becomes thinner in the powder containing Co. In the Co-added sintered magnets, the main crack brought about by Vickers indentation is comparatively easy to propagate through the grain boundaries, and microcrack branchings are rarely observed. These mechanical properties are closely related to the thickness of the damaged surface layer. Al or Ga addition to the Nd-Fe-Co-B system is very effective for obtaining a high coercive force of the powder. >

Influence of a large amount of Co substitution on the magnetic properties of NdFeCoGaB magnets (abstract)

We have found that a NdFeCoGaB sintered magnet containing 30 at. % Co still shows high coercive force in spite of such a large amount of Co substitution. The Curie temperature of the magnet is higher than that of the ternary NdFeB magnet by 280 °C. As a result, the following magnetic properties have been attained for Nd14.5Fe46Co30Ga1B8.5: Tc=590 °C, Br =11.7 kG, Hci =14.3 kOe, and (BH)max=32 MG Oe. Furthermore, in this magnet there exists an additional phase, Nd1(FeCoGa)4B1 with Ce1Co4B1 structure, which, as far as authors know, has not been reported to exist in the NdFeB‐based magnets. In this study we investigated the magnetic properties and microstructure of Nd14.5Fe76−xCoxGa1B8.5 (x=16–50) sintered magnets. The high coercive force can be obtained in the Co‐content region from 16 to 30 at. %. In particular, the magnet with 30 at. % Co shows coercive force as high as 14.3 kOe. However, further substitution of Co drastically deteriorates the magnetic properties. The coercive force of the magnet with 50 ...

Nd-Fe-B System Magnets with High Curie Temperature

Magnetic Properties of Nd-Fe-B based magnets with Co-Al or Co-Ga addition were investigated. Co-Al or Co-Ga addition increases Curie temperature and coercive force, hence, improves temperature coefficient of magnetic induction, and makes it possible to use the Nd-Fe-B magnets at a higher temperature. The coercive force of the magnets with Co and Ga increases with increasing B content, while it hardly changes with B content for Co and Al containing magnets. Also, the magnets with Co and Ga have a high coercive force of about 12 kOe even at low boron content of 3.5 at % which is far lower than that of Nd2Fe14B. Itwas shown that intrinsic coercive force IHc for Nd-Fe-B system magnets with various composition changes with temperature with a relation of IHc1/2∝T2/3.