4th INTERNATIONAL WORKSHOP ON ELECTRODEPOSITED NANOSTRUCTURES 16-18 March 2006, Dresden, Germany	ABSTRACTS

PERPENDICULAR MAGNETIC RECORDING MEDIA BY ELECTROCHEMICAL TECNIQUES S.Franz*, M.Bestetti*, A.Surpi**,#, S.Valizadeh**, L.T.Romankiw ***, P.L.Cavallotti* * Politecnico di Milano, Department of Chemistry, Materials & Chemical Engineering "G.Natta", Via Mancinelli, 7 - 20131 Milano, Italy  ** Angströmlaboratoriet, Institutionen för teknikvetenskaper- Elektronmikroskopi och nanoteknologi, Lägerhyddsvägen 1, Box 534 SE-751 21 Uppsala, Sweden  *** IBM T.J.Watson Research Center, Yorktown Heights, N.Y.10598, U.S.A. # Istituto di Fotonica e Nanotecnologie (C.N.R.), Via Cineto Romano 42, - 00156 Roma, Italy Commercial magnetic hard disk drives are based on longitudinal magnetic recording and have an areal density of about 40 Gbpsi. The recording density of hard disk drives based on longitudinal technology has increased one order of magnitude per decade from 60's to 90's. In the past 15 years, it increased from 102 Mbpsi up to 105 Mbpsi. However, the growth rate of areal density has recently slowed from about 100% to 40% per year. The reason is that the "superparamagnetic limit" for longitudinal magnetic media, which is in the range of 100 Gbpsi, is being approached. In fact, the traditional scaling-law cannot be followed because a further decrease of grain size would make the magnetic media unstable to thermal fluctuations. On the other hand, it has been demonstrated that the areal density of magnetic media based on perpendicular recording can easily be 1Tbpsi and further improvements are possible. Perpendicular magnetic recording is the only alternative to meet the requirements of increasing magnetic areal density of magnetic recording media. In order to realize such innovative magnetic recording system, a new medium is required that is significantly more complex than the current media. It must be composed of a layer having very high coercivity (HC), high saturation magnetization (MS), high HC/MS ratio, and high anisotropy constant (Ku) and a soft magnetic underlayer that is effective in writing and reading and does not contribute to the degradation of the system. Such layers have been demonstrated to be less than 500 nm thick. At the time being, three options of the new generation of perpendicular magnetic recording media were proposed: granular media, "continuous" multilayer media and patterned media. Among hard magnetic materials, CoPt alloys are the most eligible. Results concerning chemical and electrochemical deposition of CoPt thin layers - CoPt, CoPt(P), CoPtW(P) and CoPtZn(P) alloys - and ultra-thin NiFe films are presented. Composition, morphology, crystallographic structure and magnetic properties were assessed by means of EDS, SEM, AFM, XRD, XPS, PIXE, VSM and MOKE magnetometer. CoPt alloys with Pt content in the range 10-25 at.% were deposited. The crystallographic structure of CoPt alloy was hcp. Different preferred orientations (P.O.s) of the hcp structure were observed depending on the operation parameters (deposition current density, temperature, electrolyte pH and composition) and on the presence of additional alloying elements, such as W or Zn. CoPt(P) alloys were deposited from a sulphamate-based plating bath operating at pH 8 and from a chloride-based plating bath working at pH 5.4 trying to avoid resist lift-off. Co80Pt20 and CoPtW(P) alloys with Pt content in the range 9-13 at.% and W content of 3-6 at.% had strong [001] P.O. and magnetocrystalline anisotropy perpendicular to the film surface. Such films consist of magnetic grains isolated by non-magnetic materials (such as cobalt oxides and P-containing compounds) precipitated at grain boundaries, giving magnetic structures similar to patterned magnetic films. By substituting Zn for W, either [00.1] or [110] P.O.s were observed, corresponding to out-of-plane and in-plane magnetocrystalline anisotropy. Out-of-plane coercivity (HC) values of 4000 Oe and saturation magnetization (MS)values of 1150 emu/cc were measured; Hc/Ms ratio was in the range 2-5. Chemically and electrochemically deposited NiFe thin film where chosen to investigate the dependence of magnetic properties on film thickness below 100 nm. Deposition process was performed using a chloride-sulphate-based plating bath. Fe content in the permalloy varied in the range 17-35 at.%. Depending on alloy composition, easy-axis coercivity was either constant (17-20 at.% Fe) or increased (35 at.% Fe) with decreasing film thickness below 100 nm. Easy-axis coercivity values of 3-100 Oe were measured. Patterned magnetic media, where magnetic dots are recorded on pre-defined, single-domain islands of an array, are among the most proposed approaches for extending magnetic data storage limit beyond the thermal stability of conventional media. For patterning hard magnetic layers of CoPt alloys we used a focused ion beam techniques as a maskless patterning technique. As seen in figure 1 patterned nanopillars were obtained by FIB on electrochemically deposited CoPt films. Nanometric patterns of less than 80 nm wide pillars with aspect ratio of about 6 ( Figure 1- a) can be obtained. Finally, magnetic patterns obtained by Co-Pt impregnation of nanoporous silicon oxide structures will be considered, with particular regard to magnetic properties. According to preliminary hysteresis measurements, HC values of about 1700 Oe can be obtained.   a,       b, Figure 1. Co-Pt pillar arrays obtained by electrochemical deposition of Co-Pt thin films patterned by focused ion-beam lithography.

 
 
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