Mark R. Visokay

Direct formation of ordered CoPt and FePt compound thin films by sputtering

Equiatomic CoPt and FePt alloy films were deposited by cosputtering at substrate temperatures between 25 and 640 °C. Those deposited at high temperatures (≥400 and ≥520 °C for FePt and CoPt, respectively) contained ordered intermetallic compounds with the L10 crystal structure while those deposited at lower temperatures were chemically disordered. Deposition on single crystal [001] MgO and [0001] Al2O3 resulted in [001] and [111] oriented films, respectively, for all deposition temperatures. Ordered alloys have out‐of‐plane magnetic easy axes and modified magneto‐optic Kerr rotation spectra relative to the disordered case. A difference in the Kerr rotation spectrum is observed between ordered, but not disordered, [001] and [111] films.

Epitaxial PtFe(001) thin films on MgO(001) with perpendicular magnetic anisotropy

We report a technique for producing the ordered PtFe intermetallic compound with perpendicular magnetic anisotropy and a preferred c‐axis orientation perpendicular to the film plane. PtFe alloys possess high magneto‐optic Kerr rotations and magnetizations, suggesting them as likely candidates for magneto‐optic and perpendicular magnetic recording.

Epitaxial Pt(001), Pt(110), and Pt(111) films on MgO(001), MgO(110), MgO(111), and Al2O3(0001)

We have grown epitaxial Pt films, both in oxidizing and nonoxidizing environments, using planar magnetron sputtering onto heated substrates. The out‐of‐plane orientation relationships we report are Pt(001)∥MgO(001), Pt(110)∥MgO(110), Pt(111)∥MgO(111), and Pt(111)∥Al2O3(0001). We also report a seeded epitaxy technique using Fe for lower temperature epitaxial growth of Pt(001)∥MgO(001).

Characteristics and mechanism of tunable work function gate electrodes using a bilayer metal structure on SiO/sub 2/ and HfO/sub 2/

In this letter, we investigate a method to adjust the gate work function of an MOS structure by stacking two metals with different work functions. This method can provide work function tunability of approximately 1 eV as the bottom metal layer thickness is increased from 0 to about 10 nm. This behavior is demonstrated with different metal combinations on both SiO/sub 2/ and HfO/sub 2/ gate dielectrics. We use capacitance-voltage (C-V) characteristics to investigate the effect of different annealing conditions and different metal/metal bilayer couples on the work function. By comparing the as-deposited and annealed films, and by comparing with metals that are relatively inert with each other, we deduce that the work function tuning behavior likely involves metal/metal interdiffusion.

Epitaxial tetragonal PtCo (001) thin films with perpendicular magnetic anisotropy

The ordered PtCo tetragonal intermetallic compound with perpendicular magnetic anisotropy and a preferred c‐axis orientation perpendicular to the film plane has been produced by annealing epitaxial multilayers of Pt and Co. These films demonstrate large magnetic anisotropy, magneto‐optic Kerr rotations, and magnetization, suggesting them as candidates for magneto‐optic and perpendicular magnetic recording.

Epitaxial PtFe and PtCo(001) thin films with perpendicular magnetic anisotropy

Abstract We report a technique for producing the ordered PtFe and PtCo intermetallic compounds with perpendicular magnetic anisotropy and a preferred c -axis orientation perpendicular to the film plane. PtFe and PtCo alloys possess high magneto-optic Kerr rotations and magnetizations, suggesting them as likely candidates for magneto-optic and perpendicular magnetic recording.

Lorentz transmission electron microscopy study of micromagnetic structures in real computer hard disks

We have studied micromagnetic structures in real computer hard disks, with emphasis on magnetic vortices and ripples at bit-transition regions and track edges, using Lorentz transmission electron microscopy (LTEM). A combined dimpling and chemical etching was used to produce LTEM specimens of Co alloy/Cr with large, uniformly thin areas from the typical C/Co alloy/Cr/NiP/Al(substrate) hard disk structures.

Microstructural analysis of magnetic Fe/Pt multilayer thin films by transmission electron microscopy

Abstract Epitaxial Fe/Pt multilayers were deposited by sputtering onto (001) MgO. Transmission electron micrographs demonstrate the orientation relationship Fe (001)‖Pt (001) and Fe [110]‖Pt [100] in the films. Annealing produces the teteagonal ordered compound FePt with the magnetically easy c -axis oriented preferentially out of plane.

Atomically Layered Structures for Perpendicular Magnetic Information Storage

Layered structures can possess a high volumetric density of interfaces, which can result in novel magnetic properties. We report magnetic characteristics of two types of atomically layered structures, (001) oriented intermetallics with the CuAu(I) crystal structure and (111) oriented artificial multilayers. C-axis oriented superlattices of PtFe, PtCo, PdFe and PdCo with the layered CuAu(I) structure, possess large magnetic anisotropies and novel magneto-optic properties relative to the corresponding random alloys. These films are produced by annealing, with tetragonality and magnetic anisotropy developing in a fashion which depends on the initial bilayer period and annealing parameters. (111) oriented artificially grown Pd/CoCr multilayers are reported for perpendicular magnetic recording applications. Using a perpendicular contact probe transducer, the multilayers exhibit two times the readback signal of CoCr media. The multilayers can be made with low roughness suitable for contact recording, and can generate narrow readback pulses with large amplitude. Many aspects of Pd/Co performance, such as overwrite, can be predictably optimized for a given set of transducer properties. The reported results show that compositionally modulated structures can be made which have a wide variety of useful properties for perpendicular hard disk and magneto-optic recording.

Application of High-Resolution Electron Microscopy to the Study of Magnetic Thin Films and Multilayers

The performance of a wide range of modern magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt Multilayers, CO/Pt Multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron Microscopy (HREM) shows that ordered CoPt and FePt L1o structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for Magneto-optic recording Media. Different sputtering gases used in producing CO/Pt Multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.