Heng Gong

Highly oriented perpendicular Co-alloy media on Si(111) substrates

CoCrPt/Ti/Ag films with the easy axes of the hexagonal-closed-pack Co grains perpendicular to the film plane were epitaxially grown on HF-etched Si(111) single crystal substrates by rf sputter deposition. The orientation relationship was determined by x-ray pole figure measurements and transmission electron microscopy to be CoCrPt(0001)[1010]∥Ti(0001)[1010]∥Ag(111)[112]∥Si(111)[112]. The magnetic properties of the CoCrPt films were greatly improved by introducing these single crystal templates. Rocking curve measurement showed a greatly improved c-axis orientation of the cobalt alloy. Highly oriented, high coercivity properties for perpendicular recording have been obtained.

Highly oriented NiFe soft magnetic films on Si substrates

Highly oriented NiFe thin films have been produced via sputter deposition on HF etched Si substrates. Cu and Ag are used as underlayers to induce the epitaxial growth of NiFe films. The orientation relationships between NiFe, Cu, Ag, and Si have been determined by x-ray diffraction measurements and transmission electron microscopy. Magnetic properties have also been characterized.

Seed layer effects on the magnetoresistive properties of NiFe films

The effect of different seed layers on the magnetoresistive (MR) properties of NiFe films has been investigated. Significant improvements can be observed and explained. By choosing seed layers that vary from conducting to insulating and from amorphous to crystalline the role of the NiFe crystalline texture and current shunting via the seed layer on the MR ratio is observed.

Thermal stability of ultra-thin Co recording media

Ultra-thin Co/Cr films were fabricated by RF diode sputtering. The highly exchange coupled Co grains were successfully isolated by post deposition processing. The microstructure was studied with TEM and a very small physical grain size was observed. The measurement of /spl Delta/M curves showed that the grain to grain interaction changed from positive to negative. Time dependent magnetic measurements showed significant thermal decay effects. It was also found that the use of CrMn underlayers instead of pure Cr further isolated the Co grains.

Reflection high-energy electron diffraction based texture determination: Magnetic thin films for perpendicular media

Application of reflection high-energy electron diffraction (RHEED) to texture determination is demonstrated for magnetic thin film applications. Diffraction pattern analysis based on kinematic theory of RHEED is outlined. Application of the technique is demonstrated for texture characterization of hexagonal-close-packed CoCr alloys that are used as recording layers in perpendicular recording media. It is shown that both texture orientation and texture angular dispersion extracted from RHEED patterns are in agreement with the data obtained using x-ray diffraction.

Epitaxial growth of quad-crystal Co-alloy magnetic recording media

Quad-crystal CO-alloy/Cr/Ag thin film media were epitaxially grown on hydrofluric acid etched Si(111) single crystal substrates by sputter deposition. The orientation relationship was studied by x-ray θ/2θ diffraction and pole figure Φ-scan, and it was determined to be Co(1011) || Cr(ll0) || Ag(111) || Si(111). The Ag layer contains two twin-related orientations of grains. Cr grows with three variants of grains on the Ag(111) layer. Since Co(1011) contains grains with four possible easy axis directions when grown on each Cr variant, the quad-crystal media consist of grains with twelve easy axis directions and exhibit nearly isotropic in-plane magnetic properties.

New highly oriented soft magnetic underlayer structures for perpendicular recording

Highly oriented soft underlayers with face-centered-cubic (fcc) phase Co, Co alloy, and composite NiFe/Co film structures have been epitaxially grown on single crystal Si wafers by sputter deposition. The epitaxial orientation relationships have been determined by x-ray diffraction and transmission electron microscopy. It was found that the soft underlayer magnetic properties can be modified in a wide range by fine tuning the Co alloy composition or the Co alloy thickness in a NiFe/Co structure. Ti films were sputter deposited on top of the NiFe and Co layers and epitaxial growth in both Ti(0001)/Co(111) and Ti(0001)/NiFe(111) was observed. Through this highly oriented Ti intermediate layer, a Co alloy perpendicular media layer with greatly improved hexagonal-close-packed (0001) orientation can be integrated with the highly (111) textured fcc soft magnetic underlayers.

Intergranular Coupling and Grain Isolation of Thin Co Films

The effects of rapid oxidation and overcoat diffusion processes on the intergranular coupling and grain isolation in thin Co films were studied. The oxidation process was found to be strongly temperature dependent. The optimal coercivities can only be achieved within a narrow range of temperatures, while further increasing the temperature incurs significant thermal instability. CrMn underlayers were confirmed to be more effective in enhancing the grain isolation by the grain boundary diffusion during the oxidation process. The oxidation process does not change the Co anisotropy, and hence the coercivity increase is appears to be a result of better grain isolation. The in-situ diffusion of Ag and Cr overcoats were also found to have siginificant effects on the grain isolation in Co and CoCr films.

Highly Oriented Co Soft Magnetic Films on Si Substrates

Highly oriented NiFe thin films have been produced via sputter deposition on HF etched Si substrates. Cu and Ag are used as underlayers to induce the epitaxial growth of NiFe films. The orientation relationships between NiFe, Cu, Ag, and Si have been determined by x-ray diffraction measurements and transmission electron microscopy. Magnetic properties have also been characterized.

Epitaxial growth of quad-crystal Co-alloy media on Si[111]

Due to their large uniaxii anisotropy and good corrosion resistance, Co-based alloy media are the most widely used in todays longitudinal hard disk recording systems. Since the crystalline orientation of the CO alloy film directly affects the attainable coercivity and d i u m noise pmperties, control of the Orientation is a very important issue. Usually this is realized via the employment of underlayer structures Even though a number of other elements have been investigated, including the 82 NiAl structure, bcc Cr and Cr alloys are the most commonly used underlayers for this purpose. The technical literature indicares that there are three major epitaxial orientation relationships between bcc Cr and hcp CO: Co(lO.l)~~r(llO), Co(11.0)11Cr(200) and Co(lO.O)lpr(ll2). They are referred to as the quad-crystal. bi-crystal and uni-crystal structures, respectively, according to the number of possible CO c-axis orientations on a single Cr grain. The quad-crystal and bi-crystal are the more commonly obtained texture when Cr underlayers are used, while it is believed that NiAl underlayers can lead to the um-crystal.