Papers by Author: G.P. Lin

Abstract: Fe100-xPtx single-layered films with Pt contents (x) = 32~69 at.% were deposited on natural-oxidized Si(100) substrate by dc magnetron sputtering. Then the films were post-annealed at 700 °C for 3 min by a rapid thermal annealing (RTA) with a high heating ramp rate of 100 °C/sec. Experimental results show that FePt film presented (111) preferred orientation and tended to in-plane magnetic anisotropy as the content of Pt was 32 at.%. When the Pt content was increased to 55 at.%, (001)-textured FePt film was obtained and presented perpendicular magnetic anisotropy. Its out-of-plane coercivity (Hc⊥), saturation magnetization (Ms) and out-of-plane squareness (S⊥) reached to 12.7 kOe, 375 emu/cm3 and 0.8, respectively. These results reveal its significant potential as perpendicular magnetic recording media for high-density recording. Further increasing the Pt content to 69 at.%, the coercivity of FePt film was decreased drastically to below 1 kOe and tended towards in-plane magnetic anisotropy.

Abstract: The microstructures and magnetic properties of CoPt thin films with thicknesses between 1 and 20 nm deposited on amorphous glass substrate and post-annealing at 600°C for 30 min were investigated. The morphology of CoPt thin film would change from a discontinuous nano-size CoPt islands into a continuous film gradually as the film thickness was increased from 1 to 20 nm. The formation mechanism of the CoPt islands may be due to the surface energy difference between the glass substrate and CoPt alloy. Each CoPt island could be a single domain particle. This discontinuous nano-island CoPt recording film may increase the recording density and enhance the signal to noise ratio while comparing with the continuous film. The as-deposited 5 nm CoPt film revealed the separated islands morphology after annealing at 600°C for 30 min. This nano-size CoPt thin film may be a candidate for ultra-high density magnetic recording media due to its discontinuous islanded nanostructure.

Abstract: The FePt films with various thicknesses of 5 to 50 nm are deposited on Si(100) substrate without any underlayer by in-situ annealing at substrate temperature (Ts) of 620°C. A strong (001) texture of L10 FePt film is obtained and presents high perpendicular magnetic anisotropy as the film thickness increases to 30 nm. Further increasing the thickness to above 30 nm, the (111) orientation of L10 FePt is enhanced greatly, indicating that the quality of perpendicular magnetic anisotropy degrades when the FePt film is thicker than 30 nm. The single-layered FePt film with thickness of 30 nm by in-situ depositing at 620°C shows good perpendicular magnetic properties (perpendicular coercivity of 14.0 kOe, saturation magnetization of 473 emu/cm3 and perpendicular squareness of 0.96, respectively), which reveal its significant potential as perpendicular magnetic recording media for high-density recording.

Abstract: The Co3Pt magnetic layer with thickness of 7~28 nm was deposited onto the Pt underlayer. The as-deposited Co3Pt/Pt double-layered films with or without a 5 nm Pt capped layer were annealed at temperatures between 275 and 375 °C in vacuum of 1 mTorr. The influences of process parameters on perpendicular magnetic properties of Co3Pt thin films were investigated. The Co3Pt film with perpendicular coercivity (Hc⊥) value of 3620 Oe and the perpendicular squareness (S⊥) of 0.7 could be achieved from the Co3Pt(18 nm)/Pt(100 nm) double-layered films by annealing at 300°C. Further added Tb30Co70 film on the Co3Pt/Pt double-layered film could greatly enhance the perpendicular magnetic properties of the film. The Hc⊥ and S⊥ of the Tb30Co70/Co3Pt/Pt film were as high as 6560 Oe and 0.88, respectively, which has significant potential to be applied in perpendicular magnetic recording media.

Abstract: The High saturation magnetization (Ms) media are desired to yield large flux density for high resolution giant magnetoresistive head readout in Heat Assisted Magnetic Recording (HAMR). To ensure adequate stability of small size domains, the media for HAMR should possess large coercivity (Hc). In this work, we study of interface wall energy and the behavior of the magnetization of each layer in exchange coupled doubled-layered (ECDL) films. The Tb17Co83 (90 nm)/Tb30Co70 ECDL films with different Tb30Co70 thickness (20, 35, 50, 70, 90 nm) are made to increase the Ms value. As the thickness of Tb30Co70 film increase from 20 to 90 nm, the coercivity of the films increases from 2.5 to 8 kOe. The enhanced coercivity of ECDL films is due to the formation of domain wall at the interface of the ECDL film. As the Tb30Co70 increases from 20 to 90 nm, the Ms value of the films decreases from 380 to 330 emu/cm3. Due to Co has larger magnetic moment than that of Tb at room temperature, the resulting Ms value of the films decreases with increasing the thickness of Tb30Co70 layer.

Abstract: The Tb32Co68/(SiNx/Co)n films (n = 0~3) were prepared by magnetron sputtering. The magnetic anisotropy of all Tb32Co68/(SiNx/Co)n films are perpendicular to the film plane. It is found that the saturation magnetization (Ms) and perpendicular coercivity (Hc⊥ ) of the Tb32Co68/(SiNx/Co)3 film are 263 emu/cm3 and 3592 Oe, respectively. This film appears to be a promising material as a heat-assisted magnetic recording (HAMR) medium. The cross-sectional high resolution transmission electron microscope (HRTEM) images show that the interface roughness between the (SiNx/Co)n layers and TbCo layer increases as n is increased. The rough surface provides more obstacles and pinning sites that hinder the motion of the domain walls at interface between the (SiNx/Co)n layers and TbCo layer. Therefore, the Hc values are profoundly influenced by the interface roughness.

Abstract: Intensity of the (200) peak in the X-ray diffraction pattern of the MgO film increases as N2 is added to Ar gas during MgO deposition. The optimum flow rate ratio of N2 to Ar in order to obtain maximum intensity of the MgO (200) peak is 2 : 5. As introducing N2 gas, no residual nitrogen atoms are found in the MgO films, which are confirmed by AES and ESCA analysis. On the other hand, the TEM dark field image shows that the average grain size of MgO film increases with increasing the flow rate ratio of N2 to Ar. This is due to that the deposition rate of MgO film is decreased with increasing the flow rate ratio of N2 to Ar.

Abstract: Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when they use MgO as capped layer. The perpendicular magnetic anisotropy of FePt films are enhanced by introducing Ag capped layer instead of MgO capped layer. Although the in-plane coercivity (Hc⊥ ) of FePt films decreases slightly after introducing an Ag capper layer instead of a MgO capped layer, the perpendicular coercivity (Hc⊥ ) is increased significantly from 3169 Oe to 6726 Oe. The Auger electron spectroscopy analysis confirms that the Ag atoms diffuse from capped layer into the FePt magnetic layer and the Ag atoms mainly distribute at the grain boundary of FePt. This phenomenon results in the grain boundary energy enhancement and the grain growth inhibition and therefore increases the perpendicular coercivity and decrease the grain size of the FePt film.