Quantification of Perpendicular Magnetic Recording with Double Layer Media

In order to enhance the perpendicular magnetic recording characteristics of an Fe-Co-O medium with a large perpendicular anisotropy, an Fe-Co underlayer with a coercive force of about 100 Oe was investigated. The voltage reproduced from the Fe-Co-O/Fe-Co double-layered medium with the most suitable film thickness is five times as large as that for a single-layered medium. However, an Fe-Co-O/Ni-Fe double-layered medium, the underlayer of which has a higher permeability, did not show such great improvement in reproduced voltage. These results suggest that the effect of the Fe-Co underlayer is different from the decrease of demagnetization field caused by the Ni-Fe layer in a Co-Cr/Ni-Fe double-layered medium. It was also verified that Fe-Co-O/Fe-Co double-layered flexible disks have a high wear resistance, with a lifetime of more than 10 million passes without a protection layer, because of the higher stiffness and stronger adhesive force between the Fe-Co layer and the polyimide substrate.

Principal complementarity between perpendicular and longitudinal magnetic recording

Actual examples are given to show that low head impedance is extremely important in narrow track-width heads for high-density perpendicular magnetic video recording and reproduction, and that it strongly affects the wideband frequency characteristics and the noise level of the head. A main pole excitation probe-type head (MPD), with 7 μm track width, was fabricated to compare the dependence of frequency band and noise characteristics on head impedance. With high sensitivity and low impedance, the MPD head had a very favorable CN ratio of 54.5 dB, suggesting that in the future it will provide significant advantages for widebanddigital recording.

Novel FePt:C double-layered media for high density perpendicular magnetic recording were obtained. The preparation, magnetic properties, orientation mechanism, and read/write drag-testing are discussed.

Sputtered Co-Cr thin films have been extensively investigated as one of the most promising media for the perpendicular magnetic recording. In this study, the dependence of the c-axis dispersion ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on the film thickness δ has been investigated using the Facing Targets Sputtering (FTS) apparatus and the conventional DC planar magnetron sputtering (DCM) one. The films deposited by DCM exhibited a considerable dependence of ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on δ below 4,000 Å. This was mainly attributed to the bombardment of γ-electrons ejected from the central area of the target where the magnetic field is not so strong as to confine them. However, the films deposited by FTS did not show the significant dependence of ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on δ and it was less than 5 degrees even at δ as thin as 200 Å. This result indicates that the FTS system developed by the authors may be very suitable to prepare Co-Cr thin films for high density perpendicular magnetic recording media.

In this study, we focused on a FePtAu-C small-grain film specifically designed for very-high density perpendicular magnetic recording media, surpassing 1 Tbits/in2 density. The film layer had a composition of Fe47Pt43Au10-C40% with 7.2 nm thickness. It was deposited onto a silicon substrate with one 12nm thick magnesium oxide sandwich-layer at 560oC temperature. Notably, the film exhibited a perpendicular coercivity of 39 kOe. Based on transmission electron microscopy (TEM) analysis, the film small-grain size was determined to be approximately 8.2±1.6 nm. Furthermore, our investigation revealed that the grain size of magnesium oxide sandwich-layer was about 12 nm, which was larger than that of FePt. As a consequence, the FePt small-grains were not directly influenced by magnesium oxide small-grains beneath them. Moreover, a more in-depth examination using high-resolution TEM imaging demonstrated outstanding L10 ordering within the thin-film, corroborated by texture examination conducted via X-ray diffraction (XRD). It is noteworthy that magnesium oxide sandwich-layer exhibited a polycrystalline structure, while the FePt growing on top of magnesium oxide occurred in an epitaxial manner.

Summary form only given. Although, today, perpendicular magnetic recording receives substantial attention in the data storage industry, still conventional longitudinal readers (LR) are commonly used in perpendicular recording. Such a system cannot offer the optimal resolution because the LR is designed so that it is dominantly sensitive to the longitudinally written magnetization transitions. In this paper, the conformal mapping (CM) technique is used to develop a theory, which defines the guidelines on how to design an optimal perpendicular reader (PR), which is best suited for perpendicular recording. Schwartz-Christoffel transformation was used to find the requirements for optimal PR designs for providing the playback waveforms identical to the waveforms. provided by an equivalent LR in longitudinal recording. To support the theoretical conclusions, 3D boundary element modeling was developed to calculate the sensitivity field profiles for the yoke type PR and the conventional LR.

Magnetoresistive/Inductive head designs and recording characteristics were discussed in perpendicular magnetic recording. Recording by two sheets of shield showed good overwrite performance in a shielded type MR head. The head had high D50 of 100∼135kFRPI with the shield-to-shield gap of 0.5∼0.7μm. However when the recorded bit-length became shorter than the shield-to-shield gap, the shield had little effect on the medium stray field. In unshielded MR head, though large output was obtained in low density region, the output gradually decreased with increasing the recording density. However the decrease rate was much lower than that of the decrease reported in longitudinal recording. In result, the shielded type and even unshielded type MR heads offered high density recording characteristics in the contact state.

Magnetization reversal is a crucial issue to reduce a medium noise in high-density perpendicular magnetic recording. The magnetization reversal behaviors govern the writing process, zigzag transition boundary, transition jitter, and thermal stability. However, up to now, few works have been devoted to reveal magnetization behaviors by in situ MFM observation under magnetic fields, which is an extremely important issue to improvement of recording media. In this work, in-situ MFM observations were performed under various magnetic fields to make clear the magnetization reversal process microscopically. The activation volume in media was estimated by the magnetization reversal field map (MRF-map) technique, and the magnetization processes was discussed.

Perpendicular magnetic recording — progress and prospects

Increased demands for higher storage capacity solution have driven the Hard Disk Drive (HDD) technological boundaries. As the Perpendicular Magnetic Recording (PMR) head shows promising increase in Areal Density away from the limit of Longitudinal Magnetic Recording, HDD companies have switch to 100% PMR drives. PMR heads requires tight physical specifications fabricating its Writer Element in order control the magnetic flux footprint of the writer on the disk. This magnetic footprint is also called the MCW (Magnetic Core Width). MCW variations in PMR head results to significant yield loss in DET (Dynamic Electrical Test). In addition to that, continuous tweaking in Wafer and Slider Fab process to improve yield contributes to changes in MCW performance during DET. A new method that will learn and predict the MCW model accurately is thus necessary to successfully control MCW variation. An Artificial Neural Network Multilayer Perceptron architecture was developed and used to derive the MCW model from Wafer & Slider process parameters. The Artificial Neural Network model was compared with conventional Multiple Linear Regression (MLR) method and has shown that ANN gives better accuracy in predicting the final MCW than MLR by 30%.

Co–Pt thin films for magnetic recording by ECD from acidic electrolytes

The dependence of recording performance on the medium parameters in a perpendicular recording system, composed of an auxiliary pole driven head and a double layer medium, is discussed. The soft magnetic back layer behaves as part of the head to enhance the magnetic interaction between the auxiliary pole and the main pole. For excessively thick back layer and Co-Cr layer, the reproduced output decreases due to shielding effect and weakened interaction. Since the main pole head parameters also closely relate to the recording performance, it was concluded that the medium and head design should be concurrently carried out.

In order to calculate the reproduced output voltage in perpendicular recording, a reluctance method was developed. Two types of single pole thin film heads which have return paths (R Head and F Head) were fabricated and analyzed. In the analysis. three dimensional fringing flux between single pole and double layer medium was taken into consideration. Especially. calculated spacing dependence of isolated output voltage was compared with experiment, and it showed good correspondence. The analysis reveals that the output voltage is in proportion to perpendicular coercive force Hc(⊥), and the spacing between head and medium should be decreased to attain higher reproducing sensitivity.

In this article, the recording physics of a ring head with a single layered perpendicular medium (Ring/SL) is studied and the results are compared with a single pole head with a double layered perpendicular medium (SPT/DL) by using various simulations and experiments. The Ring/SL has much lower effective medium coercivity than the SPT/DL due to the substantial longitudinal field component of ring head and the incoherent rotation mode of medium magnetizations. Furthermore, switching time of the Ring/SL is estimated as only 10%∼30% of the SPT/DL. In the Ring/SL, the head field gradient of 40 Oe/nm is enough for maximizing SNR. The Ring/SL shows very low noise characteristics especially at high linear density. The signal output of the Ring/SL is smaller than the SPT/DL, but it is large enough to be detected. Therefore, it can be concluded that the combination of single layered perpendicular medium and ring head is highly promising for ultrahigh density recording.