Y.H. Fang

Microstructure and recording mechanism of Ge∕Au bilayer media for write-once optical disc

The recording mechanism of Ge∕Au bilayer and its dynamic tests for write-once blue laser high density DVD (HD DVD) are investigated. It is found that Ge2Au3 phase is nucleated between amorphous Ge and crystalline Au layer after room temperature deposition. Crystallization of Ge∕Au interface layer at 170–190°C is induced by the nucleated Ge2Au3 sites at the interface, the bilayer structure is further heated to 200–450°C. After heating above 320°C, crystallized Ge are segregated at the grain boundary. The dynamic test results show that this Ge∕Au bilayer films can be applied to 1×–2× HD DVD-R.

Improvement in hard magnetic properties of FePt films by introduction of Ti underlayer

The FePt/Ti double layer films were prepared by dc magnetron sputtering on corning glass substrates with FePt and Ti targets. The Ti underlayer with 100-nm thickness was deposited at substrate temperature 200/spl deg/C, and the FePt magnetic layer, 300 nm, was prepared at temperature from 200/spl deg/C to 600/spl deg/C for direct formation of ordered L1/sub 0/ FePt phase on the Ti underlayer. X-ray diffraction analysis showed that the [002] axis of Ti grain was perpendicular to the film plane and the FePt grains had a preferred growth of (111) plane parallel to the film plane. The degree of ordering of the FePt films increased as Ti underlayer was introduced. Magnetic property measurements indicated that the in-plane coercivities (Hc/sub /spl par//) of the FePt/Ti films in which FePt films was deposited at different temperatures were all higher than that of FePt single layer film without Ti underlayer. When the deposition temperature of FePt film was fixed at 600/spl deg/C, the Hc/sub /spl par// value of the FePt single layer film was 3.1 kOe, and it increased to 7.3 kOe as 100 nm Ti underlayer was introduced.

Microstructure and coercivity of granular nanocomposite FePt-Ag multilayer films

The face-centered-tetragonal granular L1/sub 0/FePt nanoparticles with large in-plane coercivity (Hc/sub ///) of about 3923 Oe can be achieved by an Ag-capped layer of 5-nm thickness deposited onto the FePt magnetic layer, with thickness of 20 nm, after annealing at 400/spl deg/C for 30 min. The perpendicular coercivity (Hc/sub /spl perp//) of the films is increased by increasing the annealing temperature (T/sub s/), and the Hc/sub /spl perp// value is about equal to the Hc/sub /// value when the annealing temperature is increased to 600/spl deg/C. TEM-energy disperse spectrum analysis reveals that the Ag mainly distributed at the grain boundary of FePt and results in the isolation of the FePt grains as well as the increase of the grain boundary energy, which will enhance coercivity and change the preferred orientation of the FePt film.

Optical properties of inorganic AgSb recording thin film

50nm Ag1−xSbx (x=10.8–25.5) thin films were prepared by magnetron sputtering. Thermal analysis shows that the phase change occurs around 250°C. The optical property analysis show that the as-deposited Ag80.9Sb19.1 films have high reflectivity of about 62%–73%. After heat treatment at 300°C, the contrast of Ag80.9Sb19.1 film is 12.5%–17% for wavelengths between 400 and 800nm. Dynamic test shows that using the Ag80.9Sb19.1 film as the memory layer of write once optical disk, a carrier-to-noise ratio of about 45dB can be achieved at λ=657nm, numerical aperture of 0.65, and a linear velocity of 3.5m∕s.

Microstructure and magnetic properties of CoPt-SiNx∕Ag thin films

Different amounts of amorphous SiNx nonmagnetic material and magnetic Co50Pt50 alloy were cosputtered on the different thicknesses of Ag films at room temperature then annealed at different temperatures. When the thickness of Ag underlayer is 25nm, the CoPt∕Ag film has a minimum in-plane squareness (S∥) which is about 0.35. The out-of-plane squareness (S⊥), out-of-plane coercivity (Hc⊥), and saturated magnetization (Ms) values of the CoPt∕Ag (25nm) film are about 0.95, 15kOe, and 420emu∕cm3, respectively. From the microstructure analysis of CoPt-SiNx∕Ag (25nm) films with different volume percent of SiNx content, it is found that the average grain size of CoPt decreases from about 80to9nm when the volume percent of SiNx is increased from 0% to 50%. The S⊥, Hc⊥, and Ms values of the (CoPt)50-(SiNx)50∕Ag films are about 0.5, 7.5kOe, and 200emu∕cm3, respectively.

Effects of CrRu Underlayer and CrRu Capped Layer on the Microstructure and Magnetic Properties of FePt Films

The magnetic properties and microstructure of CrRu/FePt bilayer and CrRu/FePt/CrRu trilayer deposited by dc magnetron sputtering on preheated natural-oxidized Si (100) wafer substrates were studied. It is found that both the in-plane coercivity (Hc//) and grain size of the FePt film increase with increasing the thickness of CrRu underlayer. The Hc// value of the FePt film is further increased but the grain size is decreased as adding a CrRu capped layer on the FePt film. The granular L10 FePt nanoparticles with in-plane coercivity of 2300 Oe and isolated uniform size of 6.61 nm are achieved from the CrRu(15 nm)/FePt(25 nm)/CrRu(4 nm) film deposited at a low substrate temperature of 350 degC

Magnetic properties of CoTb/FePt(001) nano-bilayer films

The magnetic properties and microstructure of CoTb/FePt bilayer films are investigated. The magnetic anisotropy of the Co70Tb30/FePt(001) film is perpendicular to the film plane. The saturated magnetization (Ms) and perpendicular coercivity () of the Co70Tb30/FePt(001) bilayer films are higher than those of single-layered Co70Tb30 films. The and Ms are 5450 Oe, and 403?emu?cm?3, respectively. As the temperature is increased to 200??C, there is a rapid decrease in the value.

Magnetic Properties and Microstructure of TbFeCoAg Amorphous Thin Films

The effect of Ag content on the magnetic properties and microstructure of Tb19.05Fe22.01Co58.94-xAgx film (x=0–18.51 at. %) were investigated. As judged from X-ray diffraction and transmission electron microscopy analyses, as-deposited Tb19.05Fe22.01Co58.94-xAgx films were amorphous. It was found that the addition of a small amount of the nonmagnetic element Ag into TbFeCo increases the saturation magnetization (Ms) and perpendicular coercivity (Hc⊥) of the film. For a Tb19.05Fe22.01Co55.75Ag3.19 film, the Ms is 268 emu/cm3, the perpendicular squareness is 0.94 and the Hc⊥ is 2058 Oe at room temperature. The Hc⊥ of the Tb19.05Fe22.01Co55.75Ag3.19 film decreases to approximately 40 Oe as temperature is increased to 200 °C. This film has potential for heat-assisted magnetic recording media applications.

Effect of SiN

The magnetic properties and microstructure of the CoPt/Ag and SiN_x/CoPt/Ag thin films deposited by dc and rf magnetron sputtering on glass substrates were studied. When the Ag underlayer is introduced to the CoPt film then annealed at 700^degC, the CoPt/Ag film has large out-of-plane squareness (S_perp), out-of-plane coercivity (H_c _perp) , and saturation magnetization(M_s), they are 0.96, 14 kOe, and 420 emu/cm³, respectively. After the SiN_x capping layer is added, it is found that the SiN_x capping layer would inhibit the CoPt (001) texture growth. The M_s value is increased due to the amount of fct CoPt phase is decreased and the inhibition of oxidation by the SiN _x capping layer. The X-ray peak intensity ratio of CoPt (001) and CoPt (111) planes ( I₀₀₁/I₁₁₁ ratio) were decreased after annealing as the SiN_x capping layer is added.

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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.