Magnetic Anisotropy Of FePt Films Research Articles

Control of Microstructure and Magnetic Properties of FePt Thin Films with TiN-MgO Intermediate Layer.

The effects of TiN-MgO intermediate layer on the microstructure and magnetic properties of FePt-SiNx-C films were investigated. With doping MgO into TiN, three components were formed, including titanium dioxide, titanium nitride and titanium oxynitride. This caused the decrease of the surface energy and the increase of the interface energy, and further induced the promotion of island growth of FePt, thus the improvement of the isolation and the decrease of FePt grains. On the other hand, the decrease of surface energy and the forming of some titanium dioxide with doping MgO would accompany the deterioration of epitaxial growth and thus the deterioration of the perpendicular magnetic anisotropy of FePt films in a certain degree. By optimizing the concentration of TiN and MgO, the FePt-SiNx-C films with small grain size of 5.86±1.03 nm and good perpendicular anisotropy would be obtained.

Effects of B additions in FePt and FePt:C films

B was co-sputtered with FePt films, leading to a granular structure; however, in addition to segregating at grain boundaries, local bonding of Fe-B was formed, which suppressed the ordering of FePt and thus degraded the perpendicular anisotropy. A boron capping layer was deposited on FePt:C (28 vol. %) films and B diffused into FePt:C grain boundaries during post-annealing. FePt:(B, C) films revealed a reduced grain size of 5.5 nm and perpendicular coercivity of 2T. Co-additions of B and C into FePt films may provide an alternative tuning knob to manipulate the microstructure and magnetic anisotropy of FePt films.

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

The single-layered Fe5.4Pt4.6 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 $L1_{0}$ FePt Films on MgO(200) Films of Varying Thicknesses

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) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> peak as well as strong (001) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> and (002) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> 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) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> peak almost disappears and both the (001) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> and (002) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> 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) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FePt</sub> 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.

Fabrication of (200)-Textured NiO Films on Glass Substrate Using Radio Frequency Sputtering

The experimental result shows that the preferred orientations of NiO thin films are closely related to the working pressure of argon. All of NiO(111), NiO(200), and NiO(220) diffraction peaks are observed in the XRD patterns and exhibited random orientation of NiO film when the film is deposited in low Ar pressure of 5 mTorr. As the Ar pressure is increased to 20 mTorr, only NiO(200) peak appears and shows (200)-textured NiO films. However, the lattice parameter of NiO film deposited in high Ar pressure of 20 mTorr is 0.424 nm, which is much larger than that of NiO bulk (0.417 nm). The lattice parameter can be decreased by post-annealing the film due to the interstitial Ar atoms are released from the NiO lattice and it reduces continuously from 0.423 to 0.417 nm as the NiO films are annealed from 300 to 600 °C. Therefore, post-annealing the NiO film deposited in higher Ar pressure will reduce the lattice misfit between the NiO and L10 FePt film that is beneficial to improve the perpendicular magnetic anisotropy of FePt film.

Effect of capped layer on microstructure and magnetic properties of FePt films

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

Microstructures and Magnetic Properties of Nanocomposite FePt Multilayer Films

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.

Microstructure and magnetic properties of nanocomposite FePt/MgO and FePt/Ag films

An in-plane magnetic anisotropy of FePt film is obtained in the MgO 5 nm/FePt t nm/MgO 5 nm films (where t=5, 10 and 20 nm). Both the in-plane coercivity ( H c∥) and the perpendicular magnetic anisotropy of FePt films are increased when introducing an Ag-capped layer instead of MgO-capped layer. An in-plane coercivity is 3154 Oe for the MgO 5 nm/FePt 10 nm/MgO 5 nm film, and it can be increased to 4846 Oe as a 5 nm Ag-capped layer instead of MgO-capped layer. The transmission electron microscopy (TEM)-energy disperse spectrum (EDS) analysis shows that the Ag mainly distributed at the grain boundary of FePt, that leads the increase of the grain boundary energy, which will enhance coercivity and perpendicular magnetic anisotropy of FePt film.

Controlling the crystallographic orientation and easy axis of magnetic anisotropy in L1 0 FePt films with Cu additive

By co-sputtering Cu and FePt onto Cr 90Mo 10 underlayers, the preferred orientation and easy axis of magnetic anisotropy of FePt films were successfully changed from the perpendicular to the in-plane direction. The pure FePt film grown on the Cr 90Mo 10 underlayer showed a (001) preferred orientation with out-of-plane magnetic anisotropy. As 20 and 40 vol.% Cu were doped, the FePt films showed a (200) preferred orientation with in-plane magnetic anisotropy. The pure FePt film showed a continuous microstructure, while the Cu-doped FePt films showed a mixture of particle-like and continuous microstructures. The change of the preferred orientation in the FePt films by Cu doping might be due to the competition of grain-boundary energy, surface free energy and epitaxial-strain energy. The experimental results suggest that the Cu doping be a promising method for the fabrication of the in-plane oriented FePt films. The Cu-doped FePt films had a lower Ms than the pure FePt film.

Modulation of preferred orientation and easy axis of magnetic anisotropy in L1 0 FePt films with Cu buffer layers

The crystallographic orientation and easy axis of magnetic anisotropy in L1 0 FePt films were successfully modulated with Cu buffer layers. The FePt film directly grown on the Cr 90Mo 10 underlayer showed a (001) preferred orientation with out-of-plane magnetic anisotropy. As the Cu buffer layer thickness was ≥4 nm, the FePt films showed a (110) preferred orientation with in-plane magnetic anisotropy. The FePt films on the Cr 90Mo 10 underlayers showed a continuous microstructure, while they showed a particle-like structure when the Cu buffer layers were used. The grain size of the FePt films increased with increasing Cu buffer layer thickness. The cross-sectional image revealed that the FePt film with 12 nm Cu buffer layer had columnar structure. The experimental results suggested that the Cu films can be a promising buffer layer for controlling the texture and easy axis of the magnetic anisotropy of FePt films.