Shinji Narishige

Distribution of blocking temperature in bilayered Ni81Fe19/NiO films

Exchange paths were investigated for unidirectional exchange coupled 40 nm Ni81Fe19/50 nm NiO films by performing several field cooling experiments. Our experimental data were very consistent with the assumed existence of a variety of exchange paths. Each exchange path seemed to produce its own local unidirectional anisotropy and different local blocking temperature. The measureable exchange coupling could be described as consisting of the sum of the respective exchange paths, each with its own local blocking temperature. On the other hand, an observed blocking temperature of about 230 °C was determined from the exchange paths having the highest local blocking temperature. The local blocking temperatures were thought to be widely distributed, ranging from room temperature to about 230 °C, and the maximum existence probability was most likely at about 215 °C. This indicated that the exchange paths having the local blocking temperature of 215 °C made the largest contribution to the exchange coupling field a...

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,...

Damping constants of Co-Cr-Ta and Co-Cr-Pt thin films

Gilberts damping constants, α , of Co-Cr-Ta and Co-Cr-Pt thin films are determined by Q-band FMR analysis using single crystal magnetic thin films epitaxialIy grown on MgO(110) substrates. α is calculated from the resonance width of the FMR spectrum. α of Co77Cr19Ta4 is found to increase from 0.016 to 0.028 as magnetic layer thickness increases from 25 to 240 nm. α also increases from 0.009 to 0.019 when the Cr concentration in the 60 nm thick Co96-x CrxTa4 magnetic layer is increased from 8 to 19 at.%. The 25 nm thick Co81Cr15Pt4, film has a 2.5 times larger α value (0.038) than the Co81Cr15Ta4 film (α = 0.014) with the same thickness.

Rotational hysteresis loss study on exchange coupled Ni81Fe19/NiO films

Investigations on unidirectional anisotropy and rotational hysteresis loss of exchange coupled Ni81Fe19/NiO films have been conducted to clarify the nature of the exchange coupling mechanism. The interfacial exchange coupling regions, which had been considered to be scattered among the nonexchange coupling regions matrix, were found to be composed of many local regions of two kinds: (i) blockable regions which can give the Ni81Fe19 film a unidirectional anisotropy and (ii) unblockable regions which can have exchange coupling, but cannot give the Ni81Fe19 film unidirectional anisotropy. These unblockable regions begin to change gradually to blockable regions on decreasing the temperature below around 100–110 K. This change is probably caused by the antiferromagnetic NiO anisotropy of unblockable regions being strengthened below that temperature. Moreover, the decrease in size of the exchange coupling field and lowered blocking temperature for tNiO<50 nm (tNiO:NiO film thickness) seems to originate from a d...

Thickness effect on ferro/antiferromagnetic coupling of Co/CrMnPt systems

To investigate ferro/antiferromagnetic coupling in Co/CrMnPt layers of spin valve films, spin valve films of glass/Ta/NiFe/CoFe/Cu/Co 30 A/CrMnPt D A/Ta 30 A were made with various CrMnPt thicknesses indicated D. Shift fields of the hysteresis loop indicated Hp and coercivities indicated Hc were evaluated. With the increase of D from 150 to 1000 A, the blocking temperature increases from RT to 340 °C. By increasing the temperature, the coercivity Hc increases, peaks at around the blocking temperature and then decreases. The temperature at which Hc peaks increases with an increase of D. The maximum value of Hc decreases with the increase of D. The grain size distribution of CrMnPt was measured and temperature dependencies of Hp and Hc were calculated based on a thermal fluctuation model using the grain size distribution. Quantitatively, the calculated results agree with the experimental results. The change of temperature dependence of Hp and Hc are explained by the change of the local blocking temperature ...

Electron spectroscopic imaging analysis of compositional inhomogeneity in CoCrTa longitudinal thin film media

The topographical nature of the compositional inhomogeneity in Co-17at.%Cr-5at.%Ta/Cr longitudinal thin film media deposited at different substrate temperature Ts, was analyzed using electron spectroscopic imaging. In the CoCrTa film deposited at high Ts, Cr segregates to the grain boundaries and intragrains, resulting in a two-dimensional network. The compositional variation grew as Ts became high. The concentration of the Cr enriched region was in the range 20-30 at.%, and that of the Cr depleted region was in the range 5-10 at.% for the sample Ts=270/spl deg/C. A strain-free CoCrTa(11.

Design and fabrication of thin‐film heads based on a dry process (invited)

High performance thin‐film heads for disk drive systems have been developed based on a dry process. Heads were computer simulated and optimal design was carried out. Relationships among Ni‐Fe composition, domain structure and wiggle of the read‐write waveform were obtained. Based on these results, optimum Ni‐Fe composition range was determined. A planarization procedure for an inbedding insulator of the conductor coil was developed. Also narrow track patterning and gap depth controlling procedures were developed. Using these procedures, a two‐layered seventeen‐turn thin‐film head for a large capacity disk drive system (23 Mb/in.2) has been developed. The head exhibited excellent read‐write characteristics.

Measurements of magnetic characteristics of thin film heads using magneto-optical method

Using a micro-Kerr magneto-optic apparatus, magnetization curves of thin film heads were measured. Relationships between repeatability of the magnetization process and readback wave form distortion were examined. In yokes made of positive magnetostriction NiFe the trianglar edge domains were found to be large, the magnetization process was not repeatable and readback wave form distortion was observed. For negative magnetostrictive yokes, the edge domains were smaller, the magnetization process was repeatable and wave form distortion was not observed.

Structures and magnetic properties of Fe/Cu multilayered films fabricated by a magnetron sputtering method

Fe and Cu single‐layered films and Fe/Cu multilayered films were prepared by an rf‐magnetron sputtering method, and the film structures and magnetic properties were investigated. Fe and Cu single‐layered films become continuous when their thickness is more than 4 nm for Fe and 10 nm for Cu. The crystal structure of Fe/Cu multilayered films depends on the thickness or continuity of Fe and Cu layers. A Fe 1.6 nm/Cu 2 nm multilayered film has a periodic structure. As the thickness of the Fe layer decreases, the magnetic flux density and coercivity decrease and the magnetostriction constant changes from negative to positive. Uniaxial magnetic anisotropy in the plane of the multilayered Fe/Cu films is observed when the Fe layer is discontinuous, but it is not clearly observed for a continuous Fe film.

Fabrication of a thin film head using polyimide resin and sputtered Ni‐Fe films

Sputter‐deposited Ni‐Fe films and planarized polyimide resin (PIQ) were used for fabrication of an eight‐turn thin film head. Properties of the head were tested using a disk storage system.