C.L. Shen

Effect of Substrate Temperature on Microstructure and Magnetic Properties of Single-Layered FePt Films

The single-layered Fe_5.4Pt_4.6 films with thickness of 30 nm are deposited directly on Si substrate at substrate temperatures (Ts) of 370 to 620°C. The single-layered FePt films incline to random orientation as the Ts is lower than 570°C. Upon increasing the substrate temperature to above 600°C, the peak intensity of (001)_FePt is much higher than that of (111)_FePt and the perpendicular squareness (S_⊥) is also much larger than that of in-plane squareness (S_//), indicating that the magnetic anisotropy of FePt film is changed from in-plane to out-of-plane. This finding reveals that a high perpendicular magnetic anisotropy of the FePt film can be obtained as the film is deposited at a higher substrate temperature of 620°C. Its perpendicular coercivity (Hc_⊥), perpendicular squareness and magnetization at 20 kOe are as high as 14.0 kOe, 0.96 and 473 emu/cm³, respectively.

Microstructure and Magnetic Properties of In-Situ Deposited

The FePt(30 nm)/MgO bilayer films with various MgO(200) underlayer thicknesses of 0 to 30 nm are in-situ deposited on Si substrates. A weak (111)FePt peak as well as strong (001)FePt and (002)FePt peaks are observed in XRD pattern of single-layered FePt film with no MgO underlayer. When a 5 nm thick MgO film is introduced under the FePt film, the (111)FePt peak almost disappears and both the (001)FePt and (002)FePt peaks are enhanced greatly. This indicates that the perpendicular magnetic anisotropy of FePt film can be improved by introduction of a thinner MgO underlayer. However, a weak (111)FePt peak appears again as the MgO underlayer is increased to 10 nm, revealing that the perpendicular magnetic anisotropy of FePt film will be deteriorated by introducing a thicker MgO underlayer.

L1_{0}

FePt thin films with different thicknesses (2.5-30 nm) were deposited alternately with Fe and Pt layers on amorphous SiO₂ substrate without any underlayer and then were postannealed at 700°C for 30 min. The dependences of microstructures, degree of ordering, and magnetic properties on FePt film thickness were investigated. The fct-FePt (001) texture films could be obtained by dc magnetron sputtering of (Fe/Pt)_n multilayer on amorphous SiO₂ substrate after annealing at 700°C for 30 min. The increasing degree of L1₀ ordering was probably due to the thicker films providing more L1₀-ordering nucleation sites. The island-like FePt grains formed on the SiO₂ substrates as the film was thinner than 7.5 nm. Both the values of out-of-plane squareness (S_⊥) and coercivity (Hc_⊥) were higher than those of in-plane ones for all film thicknesses. The values of S_⊥ are close to 1 and Hc_⊥ are in the range of 9.0-15 kOe for FePt thin films with a thickness of 5-15 nm after annealing at 700°C for 30 min.

FePt Films on MgO(200) Films of Varying Thicknesses

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.

Effect of Film Thickness on Magnetic Properties of FePt Thin Films Deposited on Amorphous

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.

{\rm SiO}_{2}

GeCu(6 nm)/Si(6 nm) bilayer recording thin film was prepared by magnetron sputtering on nature oxidized silicon wafer and polycarbonate substrate by magnetron sputtering. The thermal property, crystallization mechanism, and recording characteristics of the GeCu/Si bilayer thin film were investigated. Thermal analysis shows that the GeCu/Si bilayer thin film has two reflectivity changes with the temperature ranges, 120 °C ∼ 165 °C and 310 °C∼ 340 °C. Dynamic tests show that the optimum jitter values at recording speeds of 1X, 2X, 4X, and 5X are 5.8%, 6%, 5.9%, and 6%, respectively. It indicates that GeCu/Si bilayer film is potentially useful in write-once blu-ray optical disc.

Substrate Directly

When the Ag layer was introduced under the CoPt alloy film which annealed at 700°C, the CoPt/Ag films had large out-of-plane squareness (<i>S</i>_⊥), out-of-plane coercivity (<i>H</i>_c⊥), and saturation magnetization (<i>M</i>_s). They were 0.95, 1432 kA/m, and 390 emu/cm³, respectively. Further, the SiN_x ceramic materials were cosputtered with CoPt on the Ag underlayer at room temperature and then annealed to reduce the grain size of CoPt films. From the field-emission gun high-resolution transmission electron microscope analysis, the particle size of CoPt was about 10 nm as the SiN_x content was 46.2 vol.%. Furthermore, Ag was added into the CoPt-SiN_x films to reduce the transformation temperature of CoPt films from face-centered-cubic to face-centered-tetragonal structure.

Effect of Thicknesses on the Microstructure and Magnetic Properties of CoPt Thin Films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of ordering degree and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a well ordering degree and a perpendicular magnetic anisotropy after annealing at 700 °C for 30 min. CoPt/Ag films with a large perpendicular coercivity in the range of 13.5–14.0 kOe and a perpendicular squareness of 0.97 were obtained after annealing at 700 °C for 30 min. Ag underlayer is beneficial to enhance the perpendicular coercivity (Hc⊥) and perpendicular squareness (S⊥) of CoPt film significantly. The ordering degree and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.

Co3Pt Nanocomposite Films for Perpendicular Magnetic Recording Media

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.

Crystallization mechanism and recording characteristics of GeCu/Si bilayer for write-once blue laser optical recording

The (GeSbSn)100-xFex films (x = 0 ~ 12.9) were deposited on nature oxidized silicon wafer, and glass substrate by dc magnetron sputtering. The ZnS-SiO2 films were used as protective layers. The thickness of the (GeSbSn)100-xFex film is 100 nm. We have studied the effects of Fe addition on the crystallization kinetics, and microstructures of the GeSbSn recording film. The crystallization temperatures of (GeSbSn)100-xFex films with x = 0, 7.1, 9.1, and 12.9 were found to be 225 °C, 198 °C, 167 °C, and 165 °C, respectively. The crystallization activation energies of (GeSbSn)100-xFex films with x = 0, 7.1, 9.1, and 12.9 are about 1.74 eV, 1.15 eV, 0.81 eV, and 0.52 eV, respectively.