Double-layered Perpendicular Magnetic Recording Media Research Articles

Transition noise analysis for double-layered perpendicular magnetic recording media

Transition noise analysis for double-layered perpendicular magnetic recording media

Structure, morphology and magnetic properties of Fe–B–Si–Nb glassy alloy thin film prepared by a pulsed laser deposition method

With the aim of applying to a soft magnetic underlayer of the double-layered perpendicular magnetic recording media, an Fe 74.9B 17.5Si 2.5Nb 5.1 alloy thin film was fabricated on Si substrate by a pulsed laser deposition method. The Fe-based alloy thin film of 200 nm in thickness was confirmed as a glassy structure. The thermal properties of the thin film have similar features to those for the melt-spun glassy alloy ribbon. The glassy alloy thin film exhibits good soft magnetic properties, i.e., high B s of 1.2 T and in-plane low H c of 134 A/m. The Fe–B–Si–Nb glassy alloy thin film is expected to be suitable for the soft magnetic underlayer material in the double-layered perpendicular magnetic recording media.

Sputter-Deposited SmCo5 Thin Films with Perpendicular Magnetic Anisotropy for High Density Magnetic Recording Media

Sputter-deposited SmCo5 thin films exhibiting high perpendicular magnetic anisotropy were studied for materializing ultra high density magnetic recording. This study put emphasis on the fabrication of SmCo5 double-layered perpendicular magnetic recording media. A double-layered medium with a Ru buffer layer introduced between a Cu/Ti intermediate layer and a Co-Zr-Nb soft magnetic underlayer exhibited high perpendicular magnetic anisotropy, whereas that without the Ru buffer layer did not. Auger electron spectroscopy revealed that the Ru buffer layer inhibited unfavorable interdiffusion between the Cu/Ti intermediate layer and the Co-Zr-Nb soft magnetic underlayer. In addition, the read-write characteristics of the SmCo5 double-layered perpendicular magnetic recording media were evaluated for the first time.

Fabrication of SmCo$_{5}$ Double-Layered Perpendicular Magnetic Recording Media

We fabricated SmCo5 double-layered perpendicular magnetic recording media with high perpendicular magnetic anisotropy for realizing ultra high density recording. A double-layered medium with a Ru buffer layer introduced between a Cu/Ti intermediate layer and a Co-Zr-Nb soft magnetic underlayer exhibited high perpendicular magnetic anisotropy, whereas that without the Ru buffer layer did not. Auger electron spectroscopy revealed that the Ru buffer layer inhibited interdiffusion between the Cu/Ti intermediate layer and the Co-Zr-Nb soft magnetic underlayer. We report here for the first time the read-write characteristics of SmCo5 double-layered perpendicular magnetic recording media. The medium noise was small in the medium with a Sm-Co layer deposited under high Ar gas pressure owing to small magnetic clusters

変動成分抽出法を用いた二層膜媒体におけるスパイクのマッピング

Spike noise of double-layered perpendicular magnetic recording media with exchange-biased soft-magnetic underlayers (SULs) was studied on the basis of readback signals from a GMR head. By obtaining their averaged waveform and standard deviation, readback signals were classified into two groups: signals from the hard magnetic component and signals from the soft magnetic component. No spike was observed when the SUL retained a single domain condition: either (1) no magnetic field was applied, or (2) an external magnetic field less than the bias field was applied to the easy axis of the SUL. When an external magnetic field greater than the bias field was applied to the easy axis of the SUL, the domain wall caused spike noise with a width of a few micrometers. When an external magnetic field was applied to the hard axis of the SUL, single-peak pulses with a width of about 200 nm were observed. Since these pulses were distributed randomly in the media and the pulse density increased with increasing magnetic field, they probably originated from ripples in the SUL.

Recording performance of granular-type FePt-MgO perpendicular media

Double-layered perpendicular magnetic recording media, composed of granular-type FePt-MgO films on Fe-Ta-C soft magnetic underlayer, are fabricated on to 2.5-in glass discs with the stack structure of [MgO x-nm/FePt y-nm]/sub n//MgO 4-nm/SiO/sub 2/ 4-nm/Fe-Ta-C 200-nm/Glass disk. After annealing, granular films of FePt-MgO with high perpendicular magnetic anisotropy of the order of 10/sup 6/ erg/cc and with the texture along the film normal can be successfully fabricated. The perpendicular coercivity, magnetic activation volume, and the exchange coupling between the FePt grains are found to be strongly dependent on the initial multilayer structures and the optimum annealing conditions. The recording performance of the double-layered disks is evaluated by a spin-stand. The obtained results reveal a close correlation between the recording performance and magnetic properties.

SmCo/sub 5/-based thin films with high magnetic anisotropy for perpendicular magnetic recording

An investigation was carried out on the effects of the addition of Cu and the thickness of the SmCo/sub 5/-based thin film with perpendicular magnetic anisotropy upon its magnetic properties, with the aim of reducing the Cu/Ti underlayer thickness. As a result, the Cu/Ti underlayer thickness necessary to obtain the squareness ratio of unity was successfully reduced from 125 to 50 nm. Moreover, for the SmCo/sub 5/ double-layered perpendicular magnetic recording media with a CoZrNb soft magnetic underlayer, the Cu/Ti underlayer thickness was further reduced to 35 nm. However, the magnetic cluster size and the values of coercivity and saturation field of the SmCo/sub 5/ media were found to be too large. Thus, we recognized the need for adjusting the cluster size and the magnetic properties to appropriate values, and also the need for investigating the possibility of using this material as patterned media or thermally assisted recording media.

Development of high-performance magnetic thin film for high-density magnetic recording

This overview describes our recent study on fabrication processes of high-performance magnetic thin films for high-density magnetic recording. Particularly, it is emphasized that electrochemical processes play significant roles in fabricating the recording heads and media used for the high-density recording. Newly developed electrodeposition methods for fabricating CoNiFe and CoFe soft magnetic thin films with high-saturation magnetic flux density are shown, and the key points for obtaining them are highlighted. It is summarized that the effective seedlayers for the sputter-deposited [Co/Pd] n multilayered films, which are promising candidates as magnetic recording media with strong perpendicular magnetic anisotropy for the high-density magnetic recording, have been developed. We have recently succeeded in developing the novel electroless deposition methods for the CoNiFe-based soft magnetic underlayers of double-layered perpendicular magnetic recording media and for the patterned medium consisting of CoNiP magnetic nano-dot arrays, which are briefly explained.

In situ high temperature magnetic force microscope analysis of thermal stability in the granular-type FePt–MgO double-layered perpendicular recording media

Thermal stability of written bits with different linear densities on granular-type FePt–MgO double-layered perpendicular magnetic recording media has been investigated by magnetic force microscope (MFM) technique, equipped with an in situ heating system up to 200°C. Within the measurement time scale (∼6h), there is no observable degradation in 50- and 100-kfci bits even at 200°C indicating good thermal stability of FePt media, while in 10-kfci bits some reversed domains are found at high temperatures in the center region of the bits due to the presence of strong demagnetizing field. The average MFM signal extracted from MFM images at high temperature is interpreted based on the temperature-dependent magnetic anisotropy (Ku) behavior of the FePt media.

Methodology for investigating the magnetization Process of the storage Layer in double-Layered perpendicular magnetic recording media using the anomalous Hall effect

The Hall effect is a useful phenomenon for evaluating the magnetization processes of the storage and back layers in double-layered perpendicular magnetic recording media. Although the Hall voltage in double-layered films has two components (an anomalous Hall term arising from the perpendicular component of magnetization and a planar Hall term originating from the in-plane component of magnetization), it is possible to separate the two contributions by symmetry arguments. However, in the case where the saturation field of the recording layer (RL) is comparable to that of the soft underlayer (SUL), or when the SUL dominates the signal because of its inherently high magnetic moment, it is difficult to separate the anomalous Hall effect (AHE) contributions from the RL and SUL individually. Here we propose a methodology that overcomes this limitation and allows the extraction of the magnetization process of the RL. We assume that an average perpendicular magnetization contributes to the anomalous Hall voltage in the double-layered perpendicular media. We compare the magnetization process of the RL obtained by using this approach to that measured with a magnetooptical Kerr effect (MOKE) system. The proposed technique may be useful in those situations in which alternative tools such as the MOKE system are not suitable for measuring the magnetization process.

Electroless-deposited soft magnetic underlayer on silicon disk substrate for double-layered perpendicular magnetic recording media

A novel fabrication process of a soft magnetic underlayer (SUL) for a double-layered perpendicular magnetic recording medium was presented. The CoNiFeB SUL was deposited on a silicon disk substrate using an electroless deposition. The Ni seed layer for the electroless deposition was prepared by an electrochemical process. The surface of the deposited SUL was subjected to a chemical mechanical polishing to be flattened, and Ra value of the SUL was less than 0.4nm. A magnetic domain structure greatly depended on the electroless deposition condition. Particularly, the control of an agitation speed during electroless deposition is much effective for the suppression of distinct domain walls appearing in CoNiFeB underlayers.

An approach to estimate the magnetic anisotropy constants in a CoCrPt recording layer with a NiFe soft underlayer

To estimate the magnetic anisotropy constants (K1, K2) in a CoCrPt recording layer coexisting with a NiFe soft magnetic underlayer (SUL) in a double-layered perpendicular magnetic recording medium, application of ferromagnetic Hall effects measurement technique has been approached. Measurement of Hall voltage under the tilted magnetic field was found to be effective to surmount the difficulties in the anisotropy measurement of such a double-layered medium frequently confronted with the conventional method such as the torque magnetometry. Hall voltage response from the SUL was found to have significant effect in the determination process of K2, which necessitated the careful adjustment of the applied field direction during the measurement.

Distributions and dynamics of spike noise in double-layered perpendicular recording media

Spike noise of double-layered perpendicular magnetic recording media was studied by being classified readback signals of a GMR head into noise which comes from a recording layer and noise which comes from a soft magnetic layer. On the medium with an FeCoAlO soft magnetic underlayer, no domain structure was observed with the magnetic field which is smaller than 0.1Oe. External magnetic field induces rounded shape domains in the FeCoAlO layer from the outer edge of the medium. The size of these domains is of the order of millimeters, and the width of the domain wall is a few micro-meters. While the medium with an FeSiN soft magnetic layer has many domains. The width of the domain wall is around 0.5μm. The domain wall is moved by the magnetic field which is smaller than 0.1Oe, and is moved by the field from magnetization of recording layer.

Effect of N2 additive gas during sputtering on magnetic properties and microstructure of CoB/Pd multilayered media

Effects of N2 additive gas and/or substrate heating during the sputtering of [CoB/Pd]20 multilayered films on the magnetic properties and microstructure were investigated. The [CoB/Pd]20 film fabricated at 20°C by adding N2 gas during sputtering possessed the finest grain size and the smallest magnetic cluster size among media fabricated in this study although the film sputter-deposited at 260°C by adding N2 gas exhibited the weakest intergranular exchange coupling. It was revealed that the double-layered perpendicular magnetic recording medium that consisted of the [CoB/Pd]20 film fabricated at 20°C by adding N2 gas exhibited the highest signal-to-noise ratio in the read–write characteristics.

Double-layered perpendicular magnetic recording media of granular-type FePt–MgO films

The recording performance of double-layered granular-type FePt–MgO perpendicular magnetic recording media fabricated onto glass discs by sputtering is investigated. The (001)-textured FePt granular films are obtained by annealing FePt/MgO multilayers. Three different multilayer structures are compared in their magnetic properties and recording SNR performances. To evaluate thermal stability property of these granular-type FePt disks, the time-dependent magnetic force microscope (MFM) signal from the written bits on one of these disks is recorded in the temperature range 25–200°C. The signal decay at high observation temperature is interpreted based on the temperature dependence of magnetic anisotropy (Ku).

Simulation study of nonlinear transition shift in perpendicular magnetic recording media with increased M–H loop slope

The increase in nonlinear transition shift (NLTS) for double-layered perpendicular magnetic recording media with increased M–H loop slopes was studied using micromagnetic simulation. The simulation indicated increased NLTS for the media, but NLTS was reduced for a medium with a higher coercivity. It was concluded that increased NLTS of the media is mainly caused by the decreased write head field gradient corresponding to the decreased write field due to the increased recording sensitivity of the media. It was indicated that use of media with a higher coercivity could reduce NLTS, and an increased write head field gradient directly reduces NLTS of the media.

Effect of parameters of media on perpendicular magnetic recording properties

Effect of medium parameters on the recording properties such as write sensitivity, overwrite, recording resolution, medium noise, S/N and NLTS were experimentally investigated for Co–Cr–Pt–Nb double-layered perpendicular magnetic recording media. S/N improvement with an increase in the hysteresis loop slope parameter, α, was obtained as well as increase in the recording resolution. The increased loop slope also improved the modulation overwrite of the media where a low-frequency signal was overwritten with a high-frequency signal. The NLTS value for media with increased loop slope was found to be dominated by phase distortion which could be minimized by phase precompensation. Decrease in the intermediate layer thickness was effective to increase the S/N as well as the recording resolution, but the modulation overwrite value decreased in spite of the expected increase in the head field gradient. Permeability of the soft magnetic backlayer exhibited little effect on the recording properties.

Novel Soft Magnetic Underlayer for Double-Layered Perpendicular Magnetic Recording Media: Electroless-Deposited Films of CoNiFe-Based Alloy

We present a novel fabrication process for a soft magnetic underlayer of a CoNiFe-based alloy for a double-layered perpendicular magnetic recording medium using electroless deposition. The electroless-deposited CoNiFeP film is focused on as the soft magnetic underlayer. The CoNiFeP soft magnetic underlayer was fabricated on a 2.5-in glass disk with a Ni/Ti seed layer and the substrate was rotated in an electroless deposition bath under a magnetic field applied. The CoNiFeP underlayer as deposited was flattened using a chemical mechanical polishing, and the film thickness thereby became about 1 /spl mu/m. The in-plane coercivity and saturation magnetic flux density of the CoNiFeP underlayer were less than 2 Oe and more than 12 kG, respectively. The magnetic domain observation revealed that the CoNiFeP underlayer electroless deposited under the magnetic field applied and the substrate rotated exhibited no marked domain boundary, vanishing a spike noise in read-write experiments. A double-layered perpendicular magnetic recording medium with the electroless-deposited CoNiFeP film showed a sufficient overwrite performance and high signal-to-noise ratio as compared with a typical soft magnetic underlayer fabricated using sputtering.

Formation of Pd Nanocluster Seeds by Electrochemical Process for Control of Magnetic Properties in Co/Pd Multilayered Film

Pd cluster seeds for a double-layered perpendicular magnetic recording medium composed of a Co/Pd multilayered film and a CoZrNb soft magnetic underlayer (SUL) were fabricated with an electrochemical treatment. By immersing the SUL into an aqueous PdCl/sub 2/ solution, the substitution of Pd for Co at the surface of the SUL took place, which was caused by the difference in electrochemical redox potential between Pd and Co. Uniformly distributed Pd clusters with 8 nm in diameter were successfully formed with the treatment for the optimized duration. Use of the Pd clusters as the seeds for deposition of the Co/Pd multilayered film increased the perpendicular coercivity and reduced the size of magnetic cluster of the film. These results suggested that the Pd cluster seeds led to the formation of magnetically isolated Co/Pd multilayered grains, improving the magnetic properties of Co/Pd multilayered film.

Measurement of the Magnetic Properties of Double-Layered PMRM Using an AHE Magnetometer

The anomalous Hall effect has been recognized as a useful tool for measuring the magnetic hysteresis M(H) loops of perpendicular magnetic recording media (PMRM), and has shown particular utility for characterizing double-layered PMRM since the loops for both the recording layer (RL) and soft under layer (SUL) may be measured simultaneously, a task not easily accomplished using conventional magnetometers because of the difficulty associated with extracting the properties of the RL and SUL individually.