Perpendicular Thin Film Media Research Articles

Understanding Noise Mechanism in Small Grain Size Perpendicular Thin Film Media

One of the myths of today's perpendicular thin film media is that there is no noticeable gain in medium signal-to-noise ratio (SNR) as grain size reduces below 8 nm. A recent experimental study shows that intergranular exchange coupling exhibits an exponential dependence of the oxide grain boundary thickness for the thickness below 1 nanometer. In this paper, we present a systematic micromagnetic modeling analysis regarding the effect of spatially random intergranular exchange coupling due to the variation in grain boundary thickness. As oxide boundary becomes sufficiently thin in small grain size media, a distribution in the grain boundary thickness is found to cost significant SNR loss according to simulation results.

Characterization of Oxide Materials for Exchange Decoupling in Perpendicular Thin Film Media

We report on continued measurements using an experimental model system to quantify intergranular exchange coupling in CoCrPt-oxide perpendicular magnetic recording media. A thin film multi-layered structure comprising a high coercivity CoPt unicrystal layer separated from a low coercivity CoPt layer by a thin oxide interlayer is used to model the vertically aligned grains separated by oxide boundaries in CoCrPt-oxide media. Exchange coupling is measured by field shifts of the minor loop from the low coercivity layer. Results on coupling energy as a function of interlayer thickness are presented for several different oxides. Additional measurements are presented to understand the possible role of the added alloying elements, Cr and Mn, to the magnetic grains in terms of intergranular exchange coupling.

Grain Topography in Perpendicular Thin-Film Media and Impact of Possible Surface Anisotropy

In this paper, we present a combined transmission electron microscopy study and micromagnetic modeling investigation of current granular-continuous-composite (CGC) perpendicular thin-film media. Our transmission electron microscopy-EELS elemental analysis on CoCrPt-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layers found evident Cr segregation to the grain boundaries as well as in the middle of a grain where Co and Pt appears to be deficient. Similar localized Co and Pt deficiency is also found in CoCrPt-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> media, however, Cr segregation is much less evident. STEM-HAADF analysis reveals that the apparent non-uniform composition is the result of a ldquocavity-likerdquo topography of the magnetic grains. It is argued that the ldquocavityrdquo grain topography significantly enhances the grain boundary surface area. Micromagnetic modeling investigation was conducted to study the impact of possible surface anisotropy to the corresponding grain switching field. A systematic numerical analysis is presented.

Toward an understanding of grain-to-grain anisotropy field variation in thin film media

Grain-to-grain anisotropy field variation has become one of the main causes of medium noise, especially in perpendicular thin film media. In this paper, we present an electron microscopy investigation and theoretical analysis on the grain-to-grain anisotropy field variation in various types of thin film recording media. In alloyed film media, the intrinsic grain-to-grain composition variation would present a lower limit on grain size, thereby limiting area recording density. It is also argued that partial ordering in L1/sub 0/ materials such as FePt would yield large anisotropy field variation, especially for low values of order parameter.

Magnetic printing technique for perpendicular thin-film media with coercivity of up to 10 000 Oe

A magnetic printing technique designed for perpendicular thin-film media using a lithographically formed master disk has been presented. It is shown that magnetic printing using perpendicular hard-disk media with high coercivities of up to 10 000 Oe is satisfactorily carried out and practical printing conditions for perpendicular recording media are discussed by analyzing differences in the magnetization processes during printing processes designed for perpendicular and longitudinal media.

Variation of magnetic properties along the film thickness in perpendicular thin film media investigated by optical method

Local variation of magnetic properties along the film thickness for CoNiCrTa perpendicular thin film media is discussed based on the magneto-optical analysis. It is found that the thickness of the bottom layer, which has low coercivity, is roughly estimated to be about 10 nm. Furthermore, the hysteresis loop of the bottom layer can be calculated by using magneto-optical multilayer model.

Micromagnetic predictions of bit decay caused by thermal fluctuations over long time scales

Thermal decay in magnetic recording media increases with time, consequently decreasing the signal-to-noise ratio. A recently developed scaling technique, based on the equivalence of time and temperature within micromagnetics, has been used to predict bit decay over long time scales. An ideal square-wave field is used to record bits in thin film magnetic recording media. Comparison of bit thermal stability for longitudinal and perpendicular thin film media with similar KuV/kT is carried out at recording densities from 50 to 400 Gbit/in.2. Bit decay in a Co/Pd superlattice film at ∼100 Gbit/in.2 is also studied.

Thermal stability of magnetic recording in perpendicular thin film media

Recording and signal decay characteristics of perpendicular CoCr-alloy thin film media are investigated in comparison with those of longitudinal media. A perpendicular medium shows recording resolution 25-32% higher than that of a longitudinal medium with similar low density output. The medium S/N of a 25 nm thick perpendicular medium is comparable to that of a 16 nm thick CoCrPt longitudinal medium at high linear densities. The signal decay rate of the high Mr/Ms perpendicular medium is below 0.2% per decade of time for all linear densities. These results and thermal stability considerations based on the temperature dependence of KuV/kT indicate that CoCr-alloy perpendicular recording media are promising to extend the linear density well beyond 400 kFCI.

Micromagnetic studies of switching speed in longitudinal and perpendicular polycrystalline thin film recording media

Micromagnetic modeling is used to study the gyromagnetic switching process in longitudinal and perpendicular thin film media. Medium magnetization switching time under an applied uniform reverse field is studied by varying the damping constant α. The remanent coercivity dependence on the time duration of applied pulse field is studied for media with different inter-granular exchange coupling. At a constant recording density of 635 kfci, square wave recording is simulated with different bit cell time (0.4–4.0 ns) by varying the relative head medium linear speed from 10 to 100 m/s. The gyromagnetic switching limit on longitudinal and perpendicular media is examined at data rates from 500 MHz to 2.5 GHz with α=0.02 and 0.05. Incomplete magnetization reversal occurs for perpendicular media at a lower recording data rate than for longitudinal media.

Magnetic force microscopy images of ultrahigh-density bit patterns recorded on high-coercivity longitudinal and perpendicular thin-film media

Magnetic bit patterns recorded on high-coercivity longitudinal thin-film media (L1: Hc=2500 Oe, L2: 2850 Oe), and perpendicular thin-film media (P1: Hc=2830 Oe, P2: Hc=3780 Oe) were investigated using magnetic force microscope (MFM). For the longitudinal media, insufficient writing is responsible for limiting the detectable density. By reducing the head fly height from 3 to 2 microinches, the maximum detectable density of L1 is increased from 7000 to 10 500 fr/mm. At this density the well-defined track edge disappears and a complete bit collapse occurs as the bit length becomes much smaller than the average domain size observed in the dc-saturation remanent state. In the case of perpendicular media, contact recording provides sufficient writing and a well-defined track edge at densities above 10 000 fr/mm for both media. A maximum detectable density about 12 000 fr/mm is obtained in both media. At higher recording densities, domain refinement takes place but magnetic interactions within the track also cause the formation of large domains which eventually destroys the bit periodicity.

Narrow track recording in perpendicular thin film media

Narrow track recording in a double-layer perpendicular film medium is studied via micromagnetic modeling. A 3-D probe head field with a track width W=1.5 mu m is used for recording simulations. Recordings of multiple consecutive transitions are simulated. Edge transition patterns and edge overwrite properties are characterized. Simulated transition magnetization pattern at track edges turns towards to the head motion direction and extends to the next transition front. Edge overwrite is studied by simulating recording of a new track over a previously recorded track. It is found that the edges of the new track exhibit no separations with the overwritten track and the intertrack edge of newly recorded transitions is strongly modified by the previously written transitions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thin Film Recording Media

The rapidly growing demand for magnetic information storage systems at lower cost and higher capacity has driven the magnetic recording industry to accelerate development of thin film magnetic recording media. The ultimate recording density depends on the bit transition lengths, as shown in Figure 1 for various media, and on signal-to-noise ratio, which is proportional to the number of particles per bit. Longitudinal thin film media bit transition lengths are limited by thickness, magnetic properties, and zig-zag magnetic domain microstructures at the transitions, whereas in perpendicular media the principal limitation is the diameter of the grains. The recent development of quasi-particulate longitudinal and perpendicular thin film media indicates that areal bit densities substantially exceeding 109 bits/inch2 will be achieved in the future.This article will review magnetic phenomena relevant to thin film recording media, describe macromagnetic and micromagnetic characterization techniques, survey the development of state-of-the-art thin film media, correlate micromagnetics with magnetic properties, media noise, and recording performance, and discuss future requirements of longitudinal and perpendicular thin film recording media.Ferromagnetic and ferrimagnetic thin films exhibit a nonlinear, multivalued, and hysteretic relationship between the magnetic dipole moments per volume or magnetization M and the magnetizing field intensity H as shown in Figure 2 for the component of M in the direction of H.