Reduction of platinum acetylacetonate and thermodecomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic acid were employed in different coordinating mixtures to produce monodisperse, highly crystalline CoPt3 nanoparticles. The mean particle size can be varied from 1.5 to 7.2 nm by controlling the reaction conditions and the type of coordinating mixture. As-synthesized CoPt3 particles represent single crystal domains and have chemically disordered face-centered cubic (fcc) structure. Nearly spherical CoPt3 nanocrystals were found to assemble into two- (2D) and three-dimensional (3D) structures. An AB5 type superlattice is observed by TEM after mixing two nanoparticle samples with different mean sizes. Slow precipitation led to the formation of facetted colloidal crystals with sizes up to 20 μm.

Colloidal Synthesis and Self-Assembly of CoPt3 Nanocrystals

Co1−xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+ek2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co∼22Pt∼78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1−xPtx alloys very attractive materials for short wavelength magneto‐optic recording.

Magnetic and magneto‐optical properties of cobalt‐platinum alloys with perpendicular magnetic anisotropy

Relationship between Kerr effect and perpendicular magnetic anisotropy in Co1−xPtx and Co1−xPdx alloys

The conventional demagnetization process (spin precession, magnetic domain motion and rotation) is governed mainly by spin—lattice, magnetic dipole and Zeeman, and spin-spin interactions. It occurs on a timescale of nanoseconds. Technologically, much faster magnetization changes are always in great demand to improve data processing speed. Unfortunately, the present speed of magnetic devices is already at the limit of the conventional mechanism with little room left. Fortunately and unprecedentedly, recent experimental investigations have evidenced much faster magnetization dynamics which occurs on a femtosecond time scale: femtomagnetism. This novel spin dynamics has not been well-understood until now. This article reviews the current status of ultrafast spin dynamics and presents a perspective for future experimental and theoretical investigations.

Laser-Induced Ultrafast Demagnetization: Femtomagnetism, a New Frontier?

A systematic study of magnetic properties of CoPt alloy thin films as a function of composition and substrate deposition temperature has been carried out. The concentration dependence of the intrinsic perpendicular magnetic anisotropy constant K/sub u/ at ambient temperature reveals a maximum at about 25 at% Pt. Films of Co/sub 75/Pt/sub 25/ deposited onto Al/sub 2/O/sub 3/ (0001) substrates held at temperatures from 180/spl deg/C to 400/spl deg/C exhibit a strong perpendicular magnetic anisotropy (1.5/spl times/10/sup 7/ erg/cm/sup 3/). This strong anisotropy is closely related to the ordered state of the hcp structure.

Magnetic Properties Of Electron Beam Evaporated CoPt Alloy Thin Films

CoPt alloy films with large perpendicular magnetic anisotropy, perpendicular coercivity, and saturated perpendicular remanence are reported. These films were fabricated by e‐beam evaporation at substrate temperatures near 200 °C and above. Well‐(111)‐textured Pt underlayers are shown to dramatically increase the perpendicular magnetic anisotropy of CoPt alloy films. The large perpendicular magnetic anisotropy is shown to be strongly related to good CoPt(111) texture, and not to the ordered tetragonal Co50Pt50 phase.

C.‐J. Lin

Papers

Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy