Perpendicular Media Research Articles

A Stepped-Pole Writer to Minimize Side Erasure on Barium Ferrite Tape

Side erasure is investigated for non-oriented and perpendicularly oriented barium ferrite particulate tape media without a soft-underlayer. While notching is efficient to avoid side writing from the leading pole, the perpendicular head fields originating from the outer edge of the trailing pole result in curved transitions and non-negligible side erasure. We find that such side erasure effects can be suppressed by recessing part of the trailing pole, thereby forming a stepped pole. Magnetic force microscopy and cross-track profiling experiments demonstrate the efficacy of this novel stepped-pole writer design to minimize side writing effects in non-oriented and perpendicular particulate tape media. This writer geometry will enable tape recording at 50 ktpi and beyond.

Flat Surface Percolated Perpendicular Media With Metal Pinning Sites

The percolated perpendicular media with nonmagnetic metal pinning sites was newly developed by sputtering Ag in the deposition of [Pt/Co] multilayer. By adding Ag to this media, an approximately twofold increase in the coercivity could be achieved while keeping strong intergranular coupling and Ag is expected to function as pinning sites. The media surface was sufficiently flat to be able to fly a read/write head and this percolated media exhibited an excellent performance recordable at 750 k flux change per inch. This is the first report of such high linear density recording with the flat surface percolated perpendicular media and, with a view to further improvement, the relationship between pinning site and magnetic domain wall is discussed.

Room temperature microwave-assisted recording on 500-Gbpsi-class perpendicular medium

Microwave-assisted recording on a 500-Gbpsi-class perpendicular medium was experimentally demonstrated at room temperature. Magnetization reversal under a radio-frequency magnetic field was measured by an electrically shorted coplanar waveguide, which enabled us to evaluate the change in the medium's ferromagnetic resonance spectrum. A frequency-dependent reduction in the switching field was clearly observed in response to a microwave impulse 50 ns in duration. A significant reduction of up to 30% in the coercive field was achieved by applying a microwave impulse with an amplitude of 25 dBm and a frequency of 15 GHz.

Effects of media stray field on electromigration characteristics in current-perpendicular-to-plane giant magnetoresistance spin-valve read sensors

Effects of magnetic stray field retrieved from both longitudinal and perpendicular magnetic recording media (denoted by “media stray field”) on electromigration (EM) characteristics of current-perpendicular-to-plane (CPP) giant magnetoresistance spin-valve (GMR SV) read sensors have been numerically studied to explore the electrical and magnetic stability of the read sensor under real operation. The mean-time-to-failure (MTTF) of the CPP GMR SV read sensors was found to have a strong dependence on the physical parameters of the recording media and recorded information status, such as the pulse width of media stray field, the bit length, and the head moving velocity. According to the numerical calculation results, it was confirmed that in the longitudinal media, the shorter the stray field pulse width (i.e., the sharper the media transition) allows for the longer MTTF of the CPP GMR SV read sensors; while in the perpendicular media, the sharper the media transition gives rise to a shorter MTTF. Interestingly, it was also revealed that the MTTF could be improved by reducing the bit length as well as increasing the head velocity in both longitudinal and perpendicular media. Furthermore, the bit distribution patterns, especially the number of consecutive ‘0’ bits strongly affected the MTTF of GMR SV read sensors. The strong dependences of MTTF on the media stray field during CPP GMR SV sensor operation are thought to be mainly attributed to the thermal cycling (temperature rise and fall) caused by the resistance change due to GMR effects.

Soft layer driven switching of microwave-assisted magnetic recording on segmented perpendicular media

In this work, we use micromagnetic modeling to investigate microwave-assisted magnetic recording on segmented perpendicular media. Two types of microwave fields, sinusoidal and finite bandwidth square microwaves, have been chosen for our study. We show that microwave fields, when applied to the soft segment, can assist the magnetization reversal of the hard segment. The calculated assisted frequencies are insensitive to the variation of inter-segment exchange coupling of segmented perpendicular media. Our results suggest that sinusoidal microwave fields are practically more feasible than square microwave fields for the soft layer driven switching mechanism of segmented perpendicular media.

Influence of magnetic material composition of Fe100−xBx coated tip on the spatial resolution of magnetic force microscopy

Magnetic force microscope (MFM) tips are prepared by coating Si tips of 3 nm radius with 20-nm-thick Fe100−xBx (x = 0, 8, 18, and 34 at. %) alloys. As the B composition increases, the wettability of Fe-B alloy material to Si surface increases and a sharper and smoother MFM tip is obtained. The remanent magnetization of Fe-B alloy material decreases with increasing the B composition, which degrades the MFM signal detection sensitivity. The MFM resolution is influenced by both the tip sharpness and the remanent magnetization of coated Fe-B alloy material. Resolutions of 10.2, 9.2, 7.3, and 9.3 nm are obtained with tips coated with Fe, Fe92B8, Fe82B18, and Fe66B34 materials, respectively. Magnetic bits of 14.9 nm in length of a perpendicular magnetic medium recorded at 1700 kfci are distinguishable in the MFM image observed by using an Fe82B18-alloy coated tip. Fe-B coated tips are suitable to observe the magnetization structures of future high-density recording media.

Recording performance and thermal stability in perpendicular media with enhancement of grain isolation as well as magnetic anisotropy field

Magnetic clustering, thermal stability, and recording performance on perpendicular media with multilayered magnetic anisotropy field (Hk)-gradient CoPtCr-oxide/Cap layers with various Ru-oxide layer thicknesses (tRu-oxide) on top of Ru/NiW layers are investigated. With increasing tRu-oxide from 0 to 1.3 nm, Hc and Hs are enhanced but Hn is reduced. Magnetic correlation length (Dn) extracted from a set of major and minor loops significantly decreases but intrinsic switching field distribution remains unaffected. A short-time switching field (Ho) proportional to Hk increases linearly while KuV/kT remains unchanged. Similar KuV/kT is explained by compensation of the reduced Dn with the enhanced Ku induced by a thin Ru-oxide. However, thermal decay rate degrades from 0.06 to 0.32%/decade, which correlates well with Hn. Similar values of initial minor loop slopes indicate no change in magnetic switching behavior. A 1 nm-thick Ru-oxide layer as a well-defined granular template significantly improves recording performance: narrower MCW at 10 T by 8 nm and higher SNR at 2 T by 1.4 dB are observed even at lower OW by 8 dB compared to the media without Ru-oxide. All the recording parameters as a function of Dn correlate well.

Demonstration of microwave assisted magnetic reversal in perpendicular media

Microwave assisted magnetic reversal (MAMR) has not yet been experimentally demonstrated in hard perpendicular media. We study MAMR in perpendicular bilayer magnetic thin films and characterize the behavior as a function of frequency, power, and temperature. We find a broad frequency response with little dependence on temperature from 4 to 300 K.

Synthesis of FePt Nanocubes Using Mo(Co)<sub>6</sub> as a Reducing Agent and their Magnetic Properties

FePt thin films with perpendicularc-axis orientation have potential for application as magnetic media for data storage, In order to be used as perpendicular magnetic storage media,The chemically synthesized cubic FePt nanoparticles is easier to assembed oriented nanoarray, especially the cubic FePt nanoparticles with shape anisotropy is expected to trigger magnetic anisotropy.In this study we provide a simple method to synthesize single crystalline FePt nanoparticles with cubic shapes.The key factor to formation of cubic morphology is using Mo (Co)6as a reducing agent. As-synthesized FePt nanocubes with size that are close to 7-10nm The self-assembly FePt nanocubes are chemically disordered with face centre cubic (fcc) structure where as after annealing these particles changed to face centre tetragonal (fct) ordered structure. The phase analysis, structure, and magnetic properties were determined by X-ray diffraction (XRD), High resolution transmission electron microscope (HRTEM), Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) techniques.

Extraction of short time intrinsic switching field distributions in perpendicular media

The effects of thermal fluctuations are characterized in granular perpendicular media of two different grain sizes. We extract short time switching fields Ho and intrinsic switching field distributions and find that after correcting for thermal effects and the demagnetizing fields, the switching field distributions are almost independent of grain size, in contrast to the long time scale behavior with broader distributions observed for the small grain media. In addition, the shape anisotropy fields of the magnetic clusters are shown to decrease the observed Ho and are more significant as grain size is reduced.

Microwave-Assisted Magnetic Reversal in Perpendicular Media

Microwave-assisted magnetic reversal (MAMR) has not yet been characterized in hard perpendicular media. We investigate MAMR in such media experimentally for monolayer and bilayer magnetic thin films. The coercive field can be reduced by 8% in our geometry. The response occurs over a broad frequency range which is due to the excitation of long-wavelength spin-wave modes which can help drive reversal. Our results qualitatively match simple micromagnetic modeling.

Effect of Using Oblique-Incidence Deposited Ru Interlayers Deposited by Evaporation and Sputtering on Recording Characteristics of Perpendicular Media

Oblique-incidence evaporation and sputtering were performed to investigate the effect of reducing the Ru interlayer thickness on the recording characteristics of perpendicular magnetic recording media. Deep gaps were observed at grain boundaries on oblique-incidence evaporated and sputtered films when the incident angle was over 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> . Evaporated Ru films have a lower density than sputtered Ru films at the same incident angle. This indicates that the self-shadowing effect predominantly occurs due to suppression of migration of deposited atoms for evaporation films. However, degradation of the crystal orientation is observed in evaporated Ru films due to the present experimental limitations. Examination of the recording characteristics revealed that the Ru interlayer thickness can be reduced by using an oblique-incidence sputtered Ru interlayer and the writing ability can be improved by reducing the spacing loss between the head and the soft magnetic underlayer.

SNR Enhancement in Segmented Perpendicular Media

In this paper, we present a systematic micromagnetic modeling investigation on the segmented perpendicular thin film media. Segmented medium with inserted exchange breaking layers not only enables tunability of the crystalline anisotropy at each segment through the medium thickness, but also enables a continuous tuning of the inter-segment ferromagnetic exchange coupling strength. It is found that the switching field distribution can be significantly narrowed by optimizing the inter-segment coupling. This is because for a three-segment grain, the switching field dependence on the anisotropy field variation of the segment with highest anisotropy field can be substantially suppressed with adequate inter-segment coupling. Recording simulation shows that optimizing the inter-segment coupling strength combined with the optimization of anisotropy field for each segment, significant SNR enhancement can be achieved. Although optimizing the inter-segment coupling does yield reduction of the energy barrier, it also reduces the switching field in proportion, such that the anisotropy strength can be engineered with sufficient thermal stability. It is argued that as long as the grain size is smaller than half of the bit length, segmenting the medium grains presents an alternative and likely more effective approach than that of reducing the grain size for increasing the area density capability.

Recording Comparison of ECC versus Conventional Media at Equal Grain Size

Transition jitter and shape have been studied for “soft” exchange coupled composite (ECC) media and conventional perpendicular media using micromagnetic simulation. A realistic medium having nonuniform grain size has been employed. Media anisotropies are optimized to reduce the high density jitter for ECC and conventional media. Surprisingly, jitter is slightly decreased at high temperature for both media types. Eye diagrams show that short bit length amplitude is higher for ECC by approximately 10% at room temperature. This indicates that sharper transitions were obtained for ECC media particularly at 300 K where the thermal stability of ECC media presumably aids the write process.

Ion implantation induced modification of structural and magnetic properties of perpendicular media

This study reports the effects of implanting various doses of boron (11B+) and argon (40Ar+) ions into the recording layer and the soft underlayer of CoCrPt–SiO2-based perpendicular recording media. Implantation of a lower dose of boron ions (1011 ions cm−2) in the recording layer was found to reduce the out-of-plane coercivity, whereas no changes in the coercivity were observed when they were implanted into the soft underlayer. In the case of argon ions, lower dose implantation did not show any changes in the coercivity, irrespective of the implanted layer. However, higher dose implantations (1016 ions cm−2) of all the species were found to cause a reduction in coercivity, irrespective of the implanted layer. The reduction in coercivity was more significant when the ions were implanted in the recording layer compared with the case of implantation in the soft underlayer. X-ray diffraction (XRD) results on samples where argon was implanted in the recording layer showed a strong shift in the position of Co (0 0 .2) peaks, indicating an increase in the ‘c’ parameter. The shift is explained, on the basis of x-ray photoelectron spectroscopy, to be arising from intra-layer mixing at the CoCrPt–SiO2/Ru interface. Magnetic force microscopy images indicated an increase in domain size arising from the ion implantation.

Grain size reduction and recording performance improvement by using NiW as a partial interlayer in CoCrPt/SiO2 recording medium

We report the effect of NiW, as an interlayer to partially replace Ru, on the microstructure, magnetic properties, and recording performance of CoCrPt/SiO2 perpendicular recording media. It was found that the full width at half maximum of the rocking curves of the Co (0002) peak changed little with NiW thickness up to 10 nm. However, further increase of NiW thickness caused a larger c-axis dispersion. The grain size of the CoCrPt/SiO2 recording layer was reduced from 10.9±1.8 nm for the films without NiW to 7.7±1.5 nm for films with 10-nm NiW as a partial interlayer. The coercivity, Hc, nucleation field, Hn, and the reverse overwrite, Rev_OV, of the CoCrPt/SiO2 layer did not change much (less than 15%) with increased NiW thickness. However, it did affect the switching field distribution of the CoCrPt/SiO2 layer (more than double). The recording performance was improved by using NiW as a partial interlayer, which was mainly attributed to the reduced grain size.

Cluster size and exchange dispersion in perpendicular magnetic media

A computational study of the effects of the intergranular exchange field and its dispersion on the cluster size in perpendicular recording media is presented. The dispersion arises from the grain size dispersion and the dispersion of intrinsic exchange coupling between individual grains. It is found that increasing the degree of dispersion reduces the cluster size due to weakly coupled grains acting as pinning sites against the expansion of the clusters. A simple semi-analytical model is proposed which gives good agreement with the numerical calculations in the limit of the large anisotropy constant.

Micromagnetic study on microwave-assisted magnetic recording in perpendicular medium with intergrain exchange coupling

The influence of intergrain exchange coupling on the properties of microwave-assisted magnetization reversal has been investigated. The results of micromagnetic simulation suggest that the microwave frequency realizing the magnetization reversal is increased as the exchange stiffness constant among the magnetic grains becomes larger than 1 × 10−7 erg/cm if an inhomogeneous magnetization reversal occurred. The numerically expected increase in the microwave frequency was observed experimentally in perpendicularly magnetized Co/Pd multilayer with an exchange stiffness constant of ∼1 × 10−6 erg/cm. The simulations of signal recording and reproducing processes in a granular medium with assistance of a microwave field also suggest that an adequate intergrain exchange coupling is required to inhibit the nucleation of small island domains that will suppress the amplitude of the signal-noise ratio of the readback signal.

Recording study of percolated perpendicular media

We examine the magnetic recording properties of percolated perpendicular media (PPM) fabricated by depositing a Co/Pt multilayer film on top of nanoperforated templates created by self-assembly. We characterize the recording performance by examining the magnetic transition jitter in patterns written to the media using a hard disk drive write head. The transition jitter is lowest in the media created using the template with the highest perforation density, which demonstrates a route for further improving PPM-based recording media.

Enhanced resolution in magnetic force microscropy using tips with perpendicular magnetic anisotropy

Magnetic force microscopy (MFM) is commonly used for the characterization of magnetic nanostructures, which gets challenging for sub-20 nm features. The typical resolution of commercial MFM tips stands at about 30 nm, whereas sub-15 nm resolution has been reported by extensive modifications of the tip. In this paper, we show that a tip coated with a magnetic film possessing a perpendicular magnetic anisotropy (PMA) offers superior resolution compared to tips without PMA. The advantages of a tip with PMA have been demonstrated based on writing magnetic transitions in a commercial perpendicular media. MFM images and line scans at different scan heights are presented along with an explanation for the observed improvement in performance.