Microstructure investigations of hcp phase CoPt thin films with high coercivity

Abstract

CoPt films have been grown in the past with a high anisotropy in L11 or L10 phase, and a high coercivity is observed only in L10 CoPt films. Recently, we have grown CoPt films which exhibited a high coercivity without exhibiting an ordered phase. In this study, high resolution transmission electron microscopy (HRTEM) investigations have been carried out to understand the strong thickness and deposition pressure dependent magnetic properties. HRTEM studies revealed the formation of an initial growth layer in a metastable hexagonal (hcp) CoPt with high anisotropy. This phase is believed to be aided by the heteroepitaxial growth on Ru as well as the formation of Ru-doped CoPt phase. As the films grew thicker, transformation from hcp phase to an energetically favourable face-centered cubic (fcc) phase was observed. Stacking faults were found predominantly at the hcp-fcc transformation region of the CoPt film. The higher coercivity of thinner CoPt film is attributed to relatively less fcc fraction, less stacking faults, and to the isolated grain structure of these films compared to the thicker films.

Development of Spin-Torque Oscillators and High <inline-formula> <tex-math notation="LaTeX">${K}\!_{{u}}$ </tex-math></inline-formula> CoPt Media With Small Grain Size for Microwave-Assisted Magnetic Recording

“…Recently, K u of close to 10 7 erg/cc has been reported in Rh-doped CoPt films (with pseudo-HCP structure) which were deposited at room temperature [20]. Very recently, high coercivity was observed in equiatomic CoPt thin films with hcp phase at elevated temperature of about 350°C [21], [22].…”

Metal-oxide buffer layer for maintaining topological bumpy surface underlayer of columnar CoPt-SiO2 granular media deposited at high substrate temperature

“…In the last few years, CoPt-based alloys and oxide granular layers with high uniaxial magneto-crystalline anisotropy (K u ) have been studied widely for the first generation MAMR media. 3 In general, K u of magnetic grains are increased by implementing a postannealing process, 4,5 or by a high substrate temperature deposition process that reduces stacking faults (SFs), [6][7][8] or by realizing a compositionally modulated atomic layer structure, 9,10 or by increasing the degree of atomic site ordering. 11,12 However, when a high substrate temperature deposition process is applied to a granular layer with a magnetic alloy and a non-magnetic oxide material, such as CoPtCr-SiO 2 , lamellar and spherical grains will be induced due to the flattening of the underlayer bumpy surface by recrystallization.…”

Effect of additional elements on compositional modulated atomic layered structure of hexagonal Co80Pt20 alloy films with superlattice diffraction

“…[1][2][3][4][5][6] In practice, for current perpendicular recording medium, granular film which consists of CoPt alloy and oxide has been widely used. To increase thermal stability of the recording medium, the enhancement of K u is indispensable.…”