T.H. Sun

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}

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.

FePt Films on MgO(200) Films of Varying Thicknesses

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.

The Effect of Thickness on the Magnetic Anisotropy and Magnetic Properties of Single-Layered FePt Films by In Situ Annealing

Single-layered FePt films of 30 nm thick were annealed at temperature between 300 and 800 °C for 1–180 sec by a rapid thermal annealing (RTA) with a high heating rate of 100 °C/sec. It is found that both the grain size and magnetic domain size of the FePt film increase with increasing annealing temperature and annealing time. The FePt films exhibited soft magnetic properties and without domain images were observed by magnetic force microscope (MFM) when the films were post-annealed at below 500 °C for 180 sec. The in-plane coercivity (Hc//) and perpendicular coercivity (Hc⊥) of FePt film increases significantly to 7.5 and 6.5 kOe respectively as annealing temperature increases to 600 °C. When the annealing temperature is increased to 700 °C, they are increased to 11.1 and 9.5 kOe, respectively, and the domain structure inclines to isolated domain. However, further increasing the annealing temperature to 800 °C, the Hc// and Hc⊥ values decrease to 9.8 and 8.9 kOe respectively due to largely increase the grain size of FePt and change the domain structure from isolation to continuity. On the other hand, in order to transform the FePt film from disordered γ phase to the ordered L10 phase, the annealing time of over 3 seconds is necessary when the film was post-annealed at 700 °C with a high heating rate of 100 °C/sec by RTA technique.

Magnetic Properties of Single-Layered Fe100-xPtx Films by Rapid Thermal Annealing

Granular (FePt)100-x–(NiO)x nanocomposite thin films with x in the range of 0 – 42 vol.% were fabricated on a natural-oxidized Si(100) substrate. It is found that both the coercivity and FePt domain size decrease with increasing NiO content for the (FePt)100-x–(NiO)x films. When the FePt-NiO nanocomposite film with NiO content of 10.4 vol.% is post-annealed at 750 °C with a high heating ramp rate of 100 °C/sec, the in-plane coercivity (Hc//) and perpendicular coercivity (Hc⊥) of the FePt films are 6.4 and 5.5 kOe, respectively. On the other hand, we used conductive atomic force microscope (CAFM) to confirm that the NiO compound is distributed at grain boundary of FePt grain that will constrain the domain size of FePt and obtain isolated magnetic domains. These results indicate that NiO addition is beneficial to enhance recoding density and reduce media noise of the FePt magnetic film.