Writability issues in high-anisotropy perpendicular magnetic recording media

Challenges and recent developments associated with writability issues in high-anisotropy perpendicular recording media are reviewed. The writing field is limited by the high coercivity caused by the high anisotropy. Some new alterna- tives are proposed to solve the writability issues, including texture-tilting-assisted, domain-wall-assisted, energy-assisted magnetic recording technologies, and so on, In addition, we propose new alternatives for the next-generation of magnetic recording media.

Magnetic properties of soft layer/FePt-MgO exchange coupled composite perpendicular recording media

The magnetic properties of exchange coupled composite （ECC） media that are composed of perpendicular magnetic recording media FePt MgO and two kinds of soft layers have been studied by using an x-ray diffractometer, a polar Kerr magneto-optical system （PMOKE） and a vibrating sample magnetometer （VSM）. The results show that ECC media can reduce the coercivities of perpendicular magnetic recording media FePt-MgO. The ECC media with granular-type soft layers have weaker exchange couplings between magnetic grains and the magnetization process, for ECC media of this kind mainly follow the Stoner Wohlfarth model.

Microstructure and magnetic properties of granularFePt/(FePt)_(27)Ti_(73) films for ultrahigh-density recording media

FePt granular films were prepared by direct current facing-target magnetron sputtering system onto glass substrates and subsequently in-situ annealed in vacuum. Vibrating sample magnetometer, X-ray diffraction and scanning probe microscope were applied to study the magnetic properties, microstructures, morphologies and domain structures of the samples. （FePt）27Ti73 bilayer films were fabricated at various conditions to investigate the effect of Ti on FePt grains. The results show that without Ti matrix layer, FePt films deposited onto the glass substrates are fcc disordered; with addition of Ti matrix layer, FePt/Ti films form a ternary （FePt）27Ti73 alloy possessing fcc and L10 （111） mixed texture. FePt/（FePt）27Ti73 films with perfectly ordered L10（111） structure and unique magnetic properties can be obtained at Ti thickness of 35nm and substrate temperature of 250℃. The maximum coercivity is more than 240kA/m and the squareness ratio is more than 0.9. The obtained results suggest that the granular FePt/（FePt）27Ti73 films can be applicable to ultrahigh-density magnetic recording media.

NANO-MULTILAYERS WITH HIGH PERPENDICULAR ANISOTROPY FOR MAGNETIC RECORDING

(FePt/Ag)n nano-multilayers were deposited on MgO (100) single crystal with laser ablation and then subjected to annealing. FePt L1o grains with (001) texture and thus a large perpendicular magnetic anisotropy constant Ku of the order of 106 J/m3 were formed. A thick Ag layer is found to be favorable for decreasing the dispersion of the easy axis for magnetization. The measurement of time decay of magnetization gave rise to a small activation volume of the order of 10-25m3, showing the promising of being the recording medium for future high density perpendicular recording.

Preparation and magnetic properties of Co-P thin films

Magnetic Co-P thin films were prepared by electroless deposition. The experiment results show that the film thickness has a significant influence on the coercivity. While the film thickness varied from 300 nm to 5 μm,the coercivity dropped sharply from 45.36 to 22.28 kA/m. As the film thickness increased further,the coercivity varied slowly. When the thickness of the film was 300 nm,the deposited film could realize the coercivity as high as 45.36 kA/m,and the remanent magnetization as high as 800 kA/m .The Co-P films were deposited on the surface of magnetic drums of encoders,whose diameter was 40 mm,and then 512 magnetic poles were recorded,meaning that the magnetizing pitch was 0.245 mm. The testing results indicate that the output signals are perfect,the output waveforms are steady and the pulses account is integral. Compared with the γ-Fe2O3 coating,the Co-P thin film is suitable to be the magnetic recording media for the high resolution magnetic rotary encoder.

Preparation and Characterization of Rare Earth Metal and Alloy Target Materials for Manufacturing Magneto-Optical Disks

The studies were made on the preparation processes of the rare earth metal and alloy target materials and their characterization. In this work the rare earth metals were prepared by electrolysis of the oxide in molten salt for Nd metal and metallothermic reduction of the fluorides for Gd, Tb, Dy metals. After vacuum refining and distillation purification these rare earth metals were used for manufacturing the element targets, mosaic targets and as the starting materials of preparing the rare earth-transition metal (RE-TM) alloy targets. The four kinds of Dy-FeCo, NdDy-FeCo, Tb-FeCo and GdTb-FeCo alloy targets with diameter of 100 mm and thickness of 3 mm were prepared using powder metallurgical technique. The oxygen content and microstructure of the prepared RE-TM cast alloys and sintered targets were analyzed. The features and requirements of the RE-TM alloy sputtering target materials were also discussed.

Structural transformation of FePt nanocomposite films during annealing and its effects on magnetic properties

Fe100-xPtx(x=30at.%-60at.%) nanocomposite films were deposited on natural-oxidized Si(100) substrates by magnetron sputtering. The as-deposited films were annealed between 373 and 1073 K. In situ X-ray diffraction shows that the FePt nanocomposite films undergo a phase transformation from a disordered FCC phase to an ordered L10 phase between 673 and 773 K. The coercivity is 306 kA·m-1 whiles the average grain sizes is about 10 nm in the optimized FePt alloy film sample annealed at 673 K. The adjustable coercivity and fine grain size suggest that this FePt nanocomposites system is suitable as recording media at extremely high areal density.

Preparing Fe_5C_2 Intermetallic Compound by Mechanical Alloying Method at Room Temperature and Normal Pressure

Single phase Fe 5C 2 intermetallic compound was prepared by mechanical alloying method. The phase and crystal structure of sample were analyzed with X ray differaction spectrum. The decomposing temperature of the Fe 5C 2 compound is 596.4℃ determined by the DSC curve. It is further shown that the size of nanometer crystal grain is an important condition for carrying out the solid state reaction at room temperature and normal pressure.

Microstructure and Magnetic Properties of Sputtered Co5Sm Films

Co5 Sm/Cr bilayer films were deposited on Si and glass slides by means of a Direct-Current （DC） magnetron sputtering system with substrate heating. Magnetic properties measurements show that the sample with glass substrate has a comparatively large coercivity （He = 2 141.20e） with a rela- tively low optimal temperature （ Ts =350 ℃ ）. X-ray diffraction patterns indicate that Cr presents a hexagonal-close-packed （hcp） texture on Si, while a body-centered-cubic （bcc） struc- ture on glass substrate, which leads to Cos Sm films having dif- ferent lattice constants on Si and glass substrates. At their opti- mal temperature, the grain size of the sample on glass slide is smaller with its size distribution more uniform. Concurrently, the shape of magnetic domain is more regular and ordered. The value of magnetic switching volume （ V ） for the film on glass is 1.65×10-18 cm3 , smaller than that for films on Si. For the film on glass, the magnetization reversal mechanism is mainly influenced by magnetocrystalline anisotropy, the shape of the crystal grain and the stress in the film.

A simple 2D modulation code in single-reader two-track reading BPMR systems

A reduction in the track width of magnetic recording systems results in a welcome increase in Areal Density(AD),but can severely deteriorate system performance in the unfortunate appearance of extreme Inter-Track Interference(ITI).The effect of severe ITI may be mitigated by using coding schemes.In this paper,therefore,we present a rate-5/62-Dimensional(2D)modulation code based on a proposed Single-Reader/Two-track Reading(SRTR)technique to cope with this serious problem in staggered Bit-Pattemed Magnetic Recording(BPMR)systems.We then evaluate the Bit-Error Rate(BER)performance of the proposed system in the presence of media noises,e.g.,position and size fluctuations.Our simulation results indicate that,at the same User Density(UD),the proposed system performs better than an uncoded system by about 1.0 dB at the BER of 105 and is also superior to the conventional recording system.

Inter-granular exchange coupling and magnetic anisotropy of Ta/Ru/Co-23 at%Pt perpendicular thin films with different Ru underlayer thicknesses

In the present work, a series of Ta/Ru/Co- 23 at%Pt thin films with varied Ru underlayer thicknesses were fabricated by magnetron sputtering. All of the films show c-axis preferred orientation perpendicular to the film surface. The drop of c/a ratio and lattice expansion of Co- Pt layer with the increase in Ru underlayer thickness was revealed by X-ray diffraction （XRD）. The coercivity of the Ta/Ru/Co-Pt thin films increases drastically with Ru underlayer thickness increasing, due to the enhancement of effective magneto-crystalline anisotropy constant and exchange decoupling of magnetic nano-grains. The enhancement of effective magneto-crystalline anisotropy constant is ascribed to the lattice deformation of Co-Pt layer by mismatching the Ru layer and Co-Pt surface. Moreover, the exchange decoupling of magnetic nanograins is attributed to the further isolation of magnetic nano-grains.

Effect of Phosphor Addition on Intergranular Exchange Coupling of Co-Pt Thin Films

In this paper, ternary Co-Pt-P thin films were prepared by Co-P chips pasted on the cobalt target. The structure magnetron sputtering with platinum and home-made and magnetic properties were investigated by X-ray diffraction （XRD） and vibrating sample magnetometer （VSM）, respectively. With increasing phosphor content, the coercivities of Co-12 at.% Pt-P films increase from 1034 to 1525 Oe owing to the exchange decoupling among magnetic grains. The decrease of inter-granular exchange coupling was confirmed by delta-M curve measurement and magnetic force microscopy （MFM）. Transmission electronic microscopy （TEM） with nano- beam composition analysis shows that phosphor segregated at cobalt-based grain boundaries is responsible for the exchange decoupling. It is thus suggested that the phosphor addition is effective to tune the exchange coupling of magnetic grains, particularly for perpendicular recording media.

Abnormal saturation magnetization dependency on W content for Co-W thin films

A series of hexagonal close-packed （HCP） Co-W thin films were deposited by sputtering on surface oxidized silicon substrates at 300 ℃. A linear dependency of saturation magnetization （Ms） on W content was found up to about 9 at. pct W, and then it underwent an increased Ms vs. W content curve as compared to the initial linear dependency. The thermal magnetization technique was used to confirm that the ino creased Ms behaviour is correlated to the phase separation of the Co-W thin films. The phase separation behaviour was also found to be dependent on W content and the reason was discussed in detail. Finally an interesting composition range was suggested to be about 13 at. pct-17 at. pct W for the Co-W thin films, in which they exhibit much higher magnetic anisotropy energy than Co-Cr thin films and improved phase separation.

Correlation of Magnetic Properties of Co/Cr Bilayer Thin Films with Grain Boundary Diffusion

The microstructure and magnetic properties of Co/Cr bilayer films were examined before and after postdeposition annealing by using transmission electron microscopy （TEM）, X-ray diffraction （XRD） technique and vibrating sample magnetometer （VSM）. A model of grain boundary （GB） Cr-rich phase growth involving GB diffusion derived from the Cr underlayer was proposed to elucidate the kinetics of the paramagnetic Cr-rich phase growth along Co GBs within the Co layer. The correlation of the GB Cr-rich phase formation with the magnetic Co grain isolation and accordingly, improvement of magnetic properties was experimentally investigated and discussed in detail. Our analysis results are well consistent with previous micromagnetic simulations on the improvement of magnetic properties by the magnetic grain isolation. The results provide some insights into the processing-structure-property relationships of the Co/Cr bilayer films, and thus suggest that the magnetic grain isolation be feasible not only in longitudinal recording media, but also be effective in tuning the exchange coupling of magnetic grains in perpendicular recording media via the GB diffusion from underlayer and/or overlayer.