Density limits imposed by the microstructure of magnetic recording media

The fundamental limit of magnetic recording density on conventional media is set by the grain size. Once this grain size limit is reached, only a reduction of the grain size allows an increased SNR and thus an increased areal density. It is shown that, whilst maintaining thermal stability, scaling demands that the required anisotropy energy density K is proportional to the areal density, or the square of the areal density if the medium thickness reaches the critical thickness (A is the exchange stiffness of the material). Recording onto materials with such a high anisotropy requires some form of a write-assist. It is furthermore shown that the grain size limit cannot be obtained with intergranular exchange present, and six different requirements are listed that constitute ideal media. An alternative path for increasing areal density of magnetic recording is to use patterned media, where each bit contains only one grain. In this case, written-in errors dominate system performance and the maximum achievable areal density is estimated to be about 6 Tbit/in². Patterned media need to exhibit narrow distributions of their physical and structural properties with standard deviations of the order of 5% or less.     

The influence of annealing on the structural and magnetic properties of C/CoCrPt/CrTi trilayer recording media

Post-deposition annealing was performed on trilayer films consisting of a C overcoat layer on top of CoCrPt/CrTi/glass substrate. We observed a coercivity of 3600 Oe in the films with a 4 nm C overcoat, which was about three times larger than the coercivity of similar films without a C overcoat. This is most likely due to the significant decrease in intergranular exchange coupling for the films with C overcoat, as shown by the annealing treatment. It is believed that the diffusion of C into CoCrPt grain boundaries promotes magnetic grain isolation.     

The design of polymers for high density magnetic recording media

Polymers are responsible for a large proportion of audio/video/computer tape characteristics. Several years ago, the polymers used as a binder were selected only empirically without fundamental study. From this standpoint, the authors have systematically investigated the different effects of functional groups of various polymer binders on electromagnetic performance. As a result, it was found that the proper design of polymer binders offers significant potential for further improvement in magnetic performance. With the recent introduction of high dispersion and high durability binders, it has become clear that the particulate media like a metal tape dominates in the field of higher density recording media such as an 8 mm and Hi-8 video tape, a professional video tape like a Beta CAM SP, D2, D3, UNIHI and 1.2 Gb/s HD, and a DAT streamer tape.     

Comparison of transport and magnetic AC losses in Bi-2223/Ag tapes — the role of superconducting core geometry

AC losses were measured by 4-probe transport method and by external magnetization method in three samples of Bi-2223/Ag tape: a multifilamentary tape with separated filaments, another multifilamentary tape with ‘bridges' between filaments, and a two-shell tape. The transport losses agreed with those calculated using I_c from DC experiment. Magnetization experiments gave indications about the various paths of induced currents. For the tape with well separated filaments the main part of screening current closes inside individual filaments. Additional screening of the whole filamentary zone involves the normal metal matrix, leading to frequency dependent losses. In the case of tape with ‘bridged' filaments, supercurrents interconnect the filaments into bundles whose screening (and loss) is frequency-independent. Matching the experimental data indicates that a typical bundle was composed of 8 filaments. Magnetic losses of the two-shell tape were explained by a model for magnetization of superconducting wire with elliptical cross-section.     

Reverse draining of a magnetic soap film — Analysis and simulation of a thin film equation with non-uniform forcing

We analyze and classify equilibrium solutions of the one-dimensional thin film equation with no-flux boundary conditions and in the presence of a spatially dependent external forcing. We prove theorems that shed light on the nature of these equilibrium solutions, guarantee their validity, and describe how they depend on the properties of the external forcing. We then apply these results to the reverse draining of a one-dimensional magnetic soap film subject to an external non-uniform magnetic field. Numerical simulations illustrate the convergence of the solutions towards equilibrium configurations. We then present bifurcation diagrams for steady state solutions. We find that multiple stable equilibrium solutions exist for fixed parameters, and uncover a rich bifurcation structure to these solutions, demonstrating the complexity hidden in a relatively simple looking evolution equation. Finally, we provide a simulation describing how numerical solutions traverse the bifurcation diagram, as the amplitude of the forcing is slowly increased and then decreased.