Preparation and Magnetic Properties of Co-Pt-P Thin Films for Magnetic Recording
|Keywords||Co-Pt-P phase separation magnetic recording media magnetron sputtering|
Co-Cr-Pt recording media of hard disk drive, which is the dominant technique in magnetic recording field, subjects to superparamagnetic limit when their areal density towards Terabit/in2 density. Co-Pt alloys, which have high magnetic anisotropy energy (MAE), are good candidate for ultrahigh density magnetic recording. However, there are strong exchange coupling among magnetic grains in Co-Pt thin films. Study on magnetic recording media with high magnetic anisotropy energy (MAE) but low exchange coupling among magnetic nano-grains facilitate to overcome the superparamagnetic limit and further to increase the areal density of magnetic recording.Therefore, a novel alloy system, Co-Pt-P ternary, was studied in this work in order to control the exchange coupling. Since it is difficult to add phosphorous into Co-Pt sputtered thin films with conventional process, Co-P chips, as target elements, were first fabricated by electrodeposition. During eletrodepostion, the cathode current density and cathode current mode markedly affect microstructure of the Co-P coatings. With increasing of the cathode current density, microstructure of the Co-P coatings becomes more compact and dense, while the microstructure of Co-P coatings is of spherical particles with high porosity when the cathode current density is up to 1.5 A/cm3. Phosphorous concentrations in the Co-P coatings are mainly dependent on H3PO3 concentrations in the electrolyte rather than the cathode current density, cathode current mode and so on. The crystal structure of the Co-P coatings is also dependent on the phosphorus concentration. When the phosphorus concentration is 29at.%, the coating is of amorphous structure, while the phosphorus concentration was more than 34at.%, it becomes Co2P intermetallic compound.A series of Co-Pt and Co-Pt-P thin films with various phosphorus concentrations were then fabricated at different substrate temperatures. Their magnetic properties were measured by a vibrating sample magnetometer (VSM) and the structures were analyzed with X-ray diffraction (XRD). The main conclusions are as follow:(1) The coercivities of Co-12at.%Pt-P thin films sputtered at ambient temperature increase with the phosphorus concentration up to 4at.%. However, the films are of amorphous structure and the coercivities rapidly decrease after then. Meanwhile, the saturation magnetization decreases a little with the P addition.(2) With increasing of the substrate temperatures (Ts), in-plane coercivities of Co-12at.%Pt-2.3at.%P thin films decrease, while the perpendicular coercivities increase gradually. It is expected that phosphorous is soluble in the hcp structured Co-Pt phase.(3) The structures of Co-12at.%Pt-7at.%P thin films are strongly dependent on the Ts. It is amorphous when the Ts is up to 200℃, and then the microstructure changes into permanent magnetic phase (crystalline) and soft magnetic phase(amorphous). The structure is of fully crystalline when the Ts higher than 400℃.