A Pd/Si dual seedlayer consisting of a 5-nm-thick Pd layer on a 5-nm-thick Si layer was deposited on a substrate prior to the formation of a [Co/Pd]n multilayered perpendicular magnetic recording medium, and the effect of the deposition conditions of the dual seedlayer on the magnetic properties of the [Co/Pd]n, multilayered film was investigated. The addition of N2 to the sputtering Ar gas during the Pd upper seedlayer deposition was effective for decreasing the value of α, which is the slope of a perpendicular M-H loop, defined as 4π(dM/dH)H=Hc, and reflects the magnitude of intergranular exchange coupling The value of α was further decreased by post-annealing of the Pd/Si dual seedlayer. By combining the effects of N2 addition and the post-annealing in preparing the Pd/Si dual seedlayer, both an increase in the reproducing resolution (D50) and a reduction in the medium noise were achieved. Furthermore, the preparation conditions were found to influence the surface morphology and the state of chemical bonding of the Pd/Si dual seedlayer.
The effects of substrate temperatures during deposition and N2 gas addition to Ar sputtering gas on the magnetic properties and crystalline microstructure of Co/Pd multilayered films were investigated. The Co/Pd multilayered film deposited at a substrate temperature of 230°C with Ar containing N2 of 0.06 mTorr exhibited weaker intergranular exchange coupling than that deposited at room temperature without N2 addition. Plan-view TEM observation revealed that the crystal grains in the Co/Pd multilayered film, which was subjected to the heating process with N2 additive gas, were physically isolated by vacant grain boundaries, resulting in the decrease in intergranular exchange coupling.
Granular Fe50Pt50-Ag composite films are obtained by annealing FePt/Ag multilayer films. Upon annealing the layered structure is collapsed and L10 phase fct Fe50Pt50grains are formed. Giant magnetoresistance (GMR) effect is found in this system, which originates from the spindependent scattering of conduction electrons at the interface between FePt and Ag grains. The GMR ratio depends on the multilayer film structure and the annealing conditions, showing the correlation between the filmmicrostructure and GMR effect in granule-type composite films.
To realize higher areal density in hard disk drives (HDDs), it is necessary to develop soft magnetic materials with high saturation magnetic flux density (Bs) as pole tip materials for write heads. We have developed soft magnetic FeCoAlO films with a Bs of -2.4 T, which is close to the limit of Bs in thermal equilibrium ferromagnetic alloys. Uniaxial anisotropy is obtained in the as-made films without an applied field during sputtering. The films have sufficient magnetic thermal stability and corrosion resistance to withstand magnetic head fabrication processes. For write heads with pole tips composed of FeCoAlO films, the overwrite (O/W) is about -45 dB. Accordingly, it is established that ultrahigh Bs FeCoAlO films are effective for improving write performance.
To improve write performance at high frequency, a flattop-type head consisting of a flat upper yoke and sputtered soft magnetic films is proposed. The sputteredFeAlO films used as yoke materials are magnetically soft, and have a resistivityρ of -100 μΩcm, a saturation magnetic flux density Bs of -1.8T, and an anisotropy field Hk of -25 Oe. All of these values for the FeAlO films are higher than those of conventional plated NiFe yoke materials. The yoke thickness and length are 2μm and 18μm, respectively. A flattop-type head containing an FeAlO yoke at a high writing frequency of more than 540 Mfrps has an O/W of around -30 dB and shows good NLTS (≤15%). Consequently, the improvement of the write performance at high frequency is confirmed when plated 45-50 NiFe films are replaced by sputtered FeAlO films as yoke materials.
The magnetic vortex in a ferromagnetic disk has a unique feature of spin configuration to eliminate magnetostatic energy with a vertical bistable magnetization characteristics. We have observed magnetic vortex states in permalloy thin film disks with diameters ranging from 2μm to 25μm, using spin-polarized scanning electron microscopy (SP-SEM). Magnetic vortex states exist throughout range of diameters. At diameters larger than 15μm, multidomain states were also observed, however, a magnetic vortex state should be expected as one of the low-energy states even in a ferromagnetic disk as large as 25μm.
The magnetization and the Curie temperature of NiZn ferrite thin films deposited by sputtering are examined. As-deposited films at room temperature and 300°C are crystalline and have a spinel structure, however, theirsaturation magnetization is small and Curie temperatures are high compared to those of heat-treated films at 400-800°C. The results are explained by an assumption that the ion distribution in the as-deposited films is in a nonequilibrium state, which means a part of Zn ions occupies the B sites and the same number of Fe ions in the B sites transfers to the A sites in the spinel structure.