H. Do

Antiferromagnetically coupled magnetic recording media

Antiferromagnetically coupled (AFC) magnetic media is the current approach to extend the areal density of longitudinal recording media. The authors highlight recent measurements that characterize the write process and thermal stability of AFC media. In particular, they focus on determining the coupling and stability parameters of the individual layers and their contribution to the time scale of the write process.

Magneto-optical recording on evaporated Co/Pt multilayer films

Co/Pt multilayers composed of 0.3-nm Co and 1-nm Pt layers were prepared by e-beam evaporation from Co and Pt sources. These Co/Pt multilayers with a total film thickness of 20-30 nm have a large perpendicular magnetic anisotropy, a perpendicular hysteresis loop with a saturated remanence, a coercivity of about 1.8 kOe, and a Curie temperature of about 300 degrees C. They are structurally stable enough for thermomagnetic magnetooptical recording. Moreover, these Co/Pt multilayers are corrosion resistant and have enhanced Kerr rotation at short wavelengths. On a disk of 15*(Co(0.32 nm)/Pt(1.15 nm)) multilayer enhanced with 80-nm silicon nitride, a CNR (carrier-to-noise ratio) of 59 dB was achieved with a reading laser ( lambda =820 nm) power of 1 mW for a 2-MHz carrier at 10 m/s, and 64 dB with 3-mW read power for a 2.5-MHz carrier at 20 m/s. It is concluded that these Co/Pt multilayers are very promising as magnetooptical recording materials. >

Head challenges for perpendicular recording at high areal density

To explore recording head challenges for perpendicular recording at 200 Gb/in/sup 2/ and beyond, the design, fabrication and performance of narrow track dual-element heads were studied using an ABS trailing shield writer design and a conventional CIP-GMR reader design. Parametric recording tests of these heads on low noise CoCrPt/SUL media show that, with the trailing shield design, good writability and low disk transition jitter around 2.5 nm were achieved at narrow write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes around 1 mV and T/sub 50/ widths around 28 nm were also achieved at read trackwidths around 60 nm. The areal density potential of these heads was studied using a PRML channel at /spl sim/50 MB/s data rate. Results show linear densities around 1000 Kbpi at ontrack byte error rates of 10/sup -4/, and track densities around 200-240 ktpi using a criterion of 15% offtrack to trackpitch ratio. In all, areal densities of 210-230 Gb/in/sup 2/ were achieved with these head and disk components.

Magneto‐optical Kerr effect and perpendicular magnetic anisotropy of evaporated and sputtered Co/Pt multilayer structures

Thin and ultrathin Co/Pt multilayered structures have been prepared on glass substrates by electron‐beam evaporation at room temperature and by sputtering at various substrate temperatures and sputtering pressures. Perpendicular magnetic anisotropy was found in samples with Co/Pt bilayer thicknesses near 3 A/10 A and total thicknesses of the layer stack of no greater than 300 A. X‐ray diffraction was performed on the samples to determine layer spacing and integrity, and possible crystallinity of films. Crystalline structures in the interface between the Co and Pt layers were found and identified. The effects of sputtering parameters, such as pressure and substrate temperature, on the magneto‐optical Kerr effect were studied. The two deposition methods, electron‐beam evaporation and sputtering, resulted in different magneto‐optical properties in samples with the same nominal layer structures. We have also investigated optical properties (reflectance, index of refraction, and extinction coefficient) of these materials using ellipsometry.

Optical and magneto-optical characterization of TbFeCo thin films in trilayer structures

A series of TbFeCo films ranging in thickness from 100 to 800 A have been deposited in trilayer structures on silicon wafer substrates, with Si3N4 being employed as the dielectric material. These films have been characterized both optically and magneto‐optically by variable angle of incidence spectroscopic ellipsometry, normal angle of incidence reflectometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants n and k have been determined for the TbFeCo films, as well as the magneto‐optical constants Q1 and Q2. Results are presented that demonstrate the lack of dependence of these constants on the thickness of the TbFeCo film, and which can be used for calculating the expected optical and magneto‐optical response of any multilayer structure containing similar TbFeCo films.

Size-dependent reversal of grains in perpendicular magnetic recording media measured by small-angle polarized neutron scattering

Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt–SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter.

Coupled granular/continuous perpendicular recording media with soft magnetic underlayer

Fabrication, magnetic properties, and read/write characteristics of coupled granular/continuous (CGC) perpendicular media are described. The media consist of continuous Co/Pt multilayers, which have a strong in-plane exchange coupling, and a granular CoCrPt layer on top of a soft magnetic underlayer. These continuous and granular layers are magnetically coupled, thus the switching field distribution becomes effectively narrower. Recording measurements using a single-pole writer and a giant magnetoresistive reader show substantial improvement in the head output and resolution of the CGC medium, compared to the plain granular medium. Transition jitter and medium noise are reduced in the CGC media. As a result, the CGC media have 3–5 dB higher signal-to-noise ratio (SNR) and better thermal stability than the plain granular medium. The concept of CGC perpendicular media is a viable way to achieve both the thermal stability and medium SNR requirements for high-density recording.

Sputtering pressure effect on microstructure of surface and interface, and on coercivity of Co/Pt multilayers

Thin Co/Pt multilayers were prepared on Si and glass substrates by sputtering with Ar pressures ranging from 2.5 to 15 mTorr. The bilayer structure of the samples was Co(3 A)/Pt(15 A)×17, and all samples had the easy axis of magnetization perpendicular to the sample surface as determined with a SQUID magnetometer. All samples retained the layered structure, as revealed by low‐angle x‐ray diffraction. In addition, diffraction peaks due to the formation of Co‐Pt compounds (presumably at the interfaces between Co and Pt) were identified. The coercivity of samples changed from about 400 Oe for films deposited at low Ar sputtering pressure (2.5 mTorr) to as high as 2300 Oe for films deposited at high Ar pressure (15 mTorr). Ellipsometry and atomic force microscopy were used to study surface roughness and microstructure of samples prepared at different sputtering pressures.

Direct measurement of magnetodynamics in a perpendicular recording system

To characterize the magnetodynamic properties of a perpendicular recording system, consisting of a pole head, a recording layer, an exchangebreak layer, and a soft underlayer (SUL), we have built a test vehicle by depositing either the SUL, or the full medium stack on the air-bearing surface of the recording head. Using ultra-high-speed scanning Kerr microscopy, the intrinsic switching characteristics of the SUL and the impact of the recording layer on the former has been measured. One important feature found is the formation of vortices during reversal which are much larger than the pole area as well as evidence for spin wave excitation in the SUL. Both fast write current steps, and complex write current waveforms have been applied and significant differences of the magnetic responses are observed. Though the Kerr signal probes the temporal evolution of the SUL surface magnetization, it is possible to determine the onset of the recording layer switching by taking its magnetostatic coupling to the SUL into account. The magnetization state of the recording layer also impacts the switching speed of the SUL. The noise characteristics of the Kerr signal gives information about nonreproducible magnetization processes in the SUL.

Magnetic design evolution in perpendicular magnetic recording media as revealed by resonant small angle x-ray scattering

We analyze the magnetic design for different generations of perpendicular magnetic recording (PMR) media using resonant soft x-ray small angle x-ray scattering. This technique allows us to simultaneously extract in a single experiment the key structural and magnetic parameters, i.e., lateral structural grain and magnetic cluster sizes as well as their distributions. We find that earlier PMR media generations relied on an initial reduction in the magnetic cluster size down to the grain level of the high anisotropy granular base layer, while very recent media designs introduce more exchange decoupling also within the softer laterally continuous cap layer. We highlight that this recent development allows optimizing magnetic cluster size and magnetic cluster size distribution within the composite media system for maximum achievable area density, while keeping the structural grain size roughly constant.