Papers

AVS2001 Session MR+AS+SE-WeA: Magnetic Recording: Heads & Media

Wednesday, October 31, 2001 2:00 PM in Room 110

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		MR+AS+SE-WeA-1 Ultra-Thin Magnetic Media Overcoats through ECR Deposition M.L. Wu, J. Kiely, Y.T. Hsia, K.J. Howard (Seagate Research) With increasing demands made on the performance of ultra-thin (<3 nm) overcoats in magnetic recording media, novel deposition approaches are needed to produce films that are mechanically robust and provide corrosion resistance to the underlying media. We have used the ECR (electron cyclotron resonance) approach to create a high-density plasma and have controlled the ion energy via the bias to increase the atomic mobility and density of deposited films. Using this approach, we have deposited a series of a-C:H (N) films with thicknesses as small as 0.8 nm and correlate their corrosion, wear, and nanometer-scale scratch resistance performance with film density measurements. We also present findings that the interaction with the cobalt underlayer changes with the ECR approach. The oxidation state of the cobalt underlayer was investigated by high resolution ESCA and preliminary results showed that the percentage of cobalt oxide was significantly decreased by the ECR approach while the C (1s) spectra showed the formation of cobalt carbide at the interface. We will contrast the behavior of films deposited with this approach with those conventional sputtered a-C:H (N) films, and comment on the extendibility of traditional overcoat designs.
2:40 PM		MR+AS+SE-WeA-3 Future Directions in Magnetic Storage Technology M.H. Kryder (Seagate Research) Magnetic recording technology has advanced in areal density by over 10 million times, since it was first introduced in disk drives in 1957. Recently, the rate of progress in areal density has exceeded 100% per year, far outstripping the pace of Moore’s Law for semiconductor technology. Throughout this history there have been a number of innovations that have been made to enable the sustained progress. Today, however, we are approaching areal densities where a change in the form of the recording technology may be required. Longitudinal recording, which has been practiced in disk drives since 1957, is approaching densities at which recordings may become thermally unstable. This is forcing the industry to change the way disk drives are scaled and to consider alternative means of data storage. Technologies such as perpendicular recording, patterned media recording, optically assisted magnetic recording and probe storage are being considered. This talk will describe the methods that are being considered to extend longitudinal recording, the alternative technologies and their prospects for success.
3:20 PM		MR+AS+SE-WeA-5 Antiferromagnetically-Coupled Magnetic Media Layers for Thermally-Stable High-Density Recording E.E. Fullerton, D.T. Margulies, M. Schabes (IBM Almaden Research Center); M.F. Doerner (IBM Storage Technology Division) The combination of signal-to-noise requirements, write field limitations, and thermal activation of small particles is thought to limit the potential areal density of longitudinal recording media and is commonly referred to as the 'superparamagnetic limit'. Recording media composed of antiferromagnetically coupled (AFC) magnetic recording layers is a promising approach to extend areal densities of longitudinal media beyond these perceived limits [¹,²]. The recording medium is made up of two ferromagnetic recording layer separated by a nonmagnetic layer whose thickness is tuned to couple the layers antiferromagnetically. For such a structure, the effective areal moment density (Mrt) of the composite structure is given by the difference between the ferromagnetic layers allowing the effective magnetic thickness to scale independently of the physical thickness of the media. This allows AFC media to maintain thermal stability even for low Mrt values. Experimental realization of this concept using CoPtCrB alloy layers that demonstrates thermally stable low-Mrt media suitable for high-density recording will be discussed. ¹ ¹ E. E. Fullerton et al, Appl. Phys. Lett. 77, 3806 (2000). ² E. N. Abarra et al, Appl. Phys. Lett. 77, 2581 (2000).
4:00 PM		MR+AS+SE-WeA-7 Optimization of Media Properties in Magnetic Thin Films E.B. Svedberg, J.M. van de Veerdonk, K.J. Howard (Seagate Research); L.D. Madsen (Carnegie Mellon University) Film depositions by ultra high vacuum magnetron sputtering with controlled gradients across the wafer in terms of composition and thickness have allowed (i) efficient exploration of a large number of variables, and (ii) the interdependencies between parameters to be studied. Output parameters such as coercivity and squareness of magnetic loops for magnetic media were measured and subsequently models were extracted that incorporated both the dependencies and co-dependencies of the input parameters. An added bonus to this approach is the tight control maintained on the "fixed" parameters (e.g. temperature and background pressure) through making many samples in a single deposition. To achieve the gradients, six tilted magnetrons were used to deposit the films. In one experimental setup the effect of underlayers was studied. The samples consisted of a set of layers as follows: Ta, RuxCo1-x, CoCr, CoCrPtB. In this setup, there seems to be an optimum Ru concentration in the range of 80-85% for achieving a maximum squareness, while the coercivity increases monotonically with the Ru concentration, hence, is not possible to maximize both the coercivity and the squareness in the same disc in terms of data. In a second set of samples the effort was focused on the hard magnetic layer and investigating the effect of the additives Ta, Nb, Pt and Ti to the CoCr to promote the desired magnetic properties. From the experiments it seems that the combination of Pt and Ta/Ti additives promotes a different growth mode than Pt or the additives alone. Further, to verify the possibility of structural characterization automation, two CoCr/Pt multilayers consisting of ten bi-layers each were mapped by x-ray diffraction. In the samples, the thickness of each Pt layer was kept constant over the surface of the wafer and the thickness of the CoCr layer was varied along with the total thickness.
4:20 PM		MR+AS+SE-WeA-8 Magnetic Nanoparticles and Nanoparticle Assemblies S. Sun (IBM Research) We present our chemical synthetic approaches to monodisperse magnetic nanoparticles (Co and FePt) and nanoparticle superlattices. Advances of magnetic recording technology have driven the development of new magnetic nanoparticle-based media with uniformity in both particle size and particle magnetics. Self-assembly of magnetic nanoparticles may offer an easy way of fabricating such media. The key step for successful self-assembly approach is to use structurally stabilized magnetic nanoparticles as building blocks to form uniform nanoparticle arrays. We have found that steric repulsion from long chain hydrocarbon surfactants is effective in particle stabilization process. A combination of surfactants such as trialkylphosphine/oleic acid (for Co) and oleic acid/oleyl amine (for FePt) has been successfully employed to control particle growth, stabilize the particles, and protect them from oxidation. The particles can be prepared by metal salt reduction and metal carbonyl decomposition. By varying metal/surfactant or metal/metal ratio, both particle size (2-11nm) and alloy composition can be tuned. These monodisperse magnetic nanoparticles can self-organize into regularly arrayed magnetic superlattices. Microscopic studies of the assemblies have shown that the symmetry of these assemblies is dependent upon many factors including particle's size and shape. Thermal annealing is applied to adjust interparticle spacing of the superlattice assemblies and to control internal particle structure. Magnetic properties of these assemblies can be easily tuned from superparamagnetic to ferromagnetic. These well-controlled magnetic nanoparticle assemblies are of interest for future fabrication of nanoelectronic devices, and will have great potential for ultra-high density magnetic recording.
5:00 PM		MR+AS+SE-WeA-10 Thermal Stability of Granular Perpendicular Magnetic Islands Patterned using a Focused Ion Beam S. Anders, C.T. Rettner, M.E. Best, B.D. Terris (IBM Almaden Research Center) We have studied the thermal stability of patterned magnetic media islands as a function of island size. A focused ion beam (30 keV, Ga+) was used to pattern granular CoCrPt media to produce square arrays of islands of different periods, ranging from 70-750 nm. Islands with periods smaller than 130 nm appear as single magnetic domains in MFM images, while larger islands show multi-domain behavior. The samples were magnetized perpendicularly in a field of 20 kOe (far in excess of the ~3 kOe coercivity) to produce fully magnetized films. This fully magnetized state should have the highest decay rate, since the demagnetization field is maximized. Magnetic force microscopy images taken at various times after the magnetization show that the patterned structures have a considerably slower thermal decay rate than the unpatterned film. Small single-domain islands were seen to have the smallest decay rate of less than 0.25% per decade compared to one order of magnitude higher decay rates for the unpatterned media. This enhanced stability is analyzed in terms of increased demagnetization fields and increased switching volumes introduced by patterning.