Hexagonal Barium Ferrite Thin Films Research Articles

Magnetic Properties of Hexagonal Barium Ferrite Films on Pt(111)/Al2O3(0001) Substrate Based on Optimized Thickness of Pt

In this study, hexagonal barium ferrite thin films have been deposited on Pt(111)/Al2O3(0001) substrates by pulsed laser deposition. The thickness of Pt dependence of crystallographic structure and magnetic properties has been studied. X-ray diffraction θ-2θ reveals the films have a good c-axis orientation perpendicular to the film plane. Furthermore, pole figure analysis discovers that the crystallinity of films is greatly improved by Pt buffer layer and the highest degree of orientation is prepared at 20-nm-thick Pt. It is also observed from scanning electron microscope and atomic force microscopy that the BaM film with 20-nm-thick Pt is formed as hexagonal shaped and has smaller than 2 nm of roughness. Magnetic hysteresis loops show the saturation magnetization ( ${\rm{M}}_{{\rm{s}}}$ ), coercivity ( ${\rm{H}}_{{\rm{c}}}$ ), and uniaxial anisotropy field ( ${\rm{H}}_{{\rm{k}}}$ ) are greatly depended on the thickness of Pt buffer layer. Consequently, films with 20-nm Pt buffer layer have the highest ${\rm{M}}_{{\rm{s}}}$ of ${\rm{358\,emu/ cm}}^{3}$ and ${\rm{H}}_{{\rm{k}}}$ of 16.7 kOe which are comparable with the theoretical value of BaM bulk.

Magnetic properties of hexagonal barium ferrite films on Pt/MgO(111) substrates annealed at different temperatures

In this work, hexagonal barium ferrite thin films have been deposited on Pt/MgO(111) substrates by pulsed laser deposition. The anneal temperature dependence of crystal structures, extents of diffusion and magnetic properties have been studied. X-ray diffraction patterns reveal that the crystal structure changes from the hexagonal to the spinel when the anneal temperature increases. The texture with c-axis perpendicular to the film plane and the small c-axis dispersion angles (△ɵc) have been obtained in the film annealed at 950 °C for 10h. Both the X-ray photoelectron spectroscopy profiles and energy dispersive spectrometer show that the diffusions of Mg2+and Fe3+cations are more obvious when the annealing temperature is higher than 950°C. The film annealed at 950°C show anisotropic and hard magnetic properties. The magnetic properties of film annealed at 1050°C are soft.

Morphology control of barium ferrite thin films

Hexagonal barium ferrite thin films were fabricated by spin coating of precursors obtained by sol-gel methods onto sapphire (00l) faces. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used to tune the morphology of the films. The films show texture with c-axis normal to the film plane as shown by the strong x-ray diffractions from the (001) plane with full width at half maximum of the rocking curves about 0.4°. The [100] direction of the film is parallel to the [110] direction of the sapphire. With the increase of the citric acid, the percentage of the acicular crystallites increased. EDTA can be used to produce films with the best texture where faceted grains were obtained. The maximum coercive force obtained was about 302 kA/m.

Development of nanograined hexagonal barium ferrite thin films by sol–gel technique

Nanograined hexagonal barium ferrite (BaFe 12O 19) thin films have been developed on naturally oxidized Si substrates by sol–gel technique using aqueous solution of metal chlorides. Coated films were heat treated at different temperatures ranging from 450 to 900 °C, and all the films were characterized by using X-ray diffraction (XRD), inductive coupled plasma (ICP) spectroscopy, and field emission scanning electron microscopy (FESEM). The effects of temperature on the formation of BaFe 12O 19 thin film were studied, and it was observed that hexagonal barium ferrite thin films with grain sizes of about 50 nm were formed above 700 °C. Study on the magnetic properties of the films by vibrating sample magnetometer (VSM) showed that films exhibited large saturation magnetization and high coercivity in the range 247–355 emu/cm 3 and 2.70–4.22 kOe, respectively, while the Curie temperatures ( T c) were in the range 443–457 °C. The effects of temperatures on the magnetic properties were also studied.

Microstructure and magnetic properties of hexagonal barium ferrite thin films with various underlayers

BaM (barium ferrite) thin films and underlayers (Fe, Cr, Al2O3, Fe2O3, ZnFe2O4, TiO2) were prepared by rf/dc magnetron sputtering on (100) oriented bare Si substrates. The effects of the underlayer on grain orientation, magnetic properties, and microtexture of BaM film were studied. All the BaM films, except BaM/Fe/Si film, attained nearly the same perpendicular and in-plane coercivities. The BaM/TiO2/Si exhibits the highest coercivity. However, regardless of the underlayer, BaM grains are randomly oriented. By adopting ZnFe2O4 as an underlayer, the interdiffusion of Si from substrate was prohibited to some degree. Elongated grains from the extinction of small platelet grains were grown with an increase in the BaM film thickness of BaM/Si. The microstructure of BaM in BaM/TiO2/Si was strongly dependent on both the microstructure of TiO2 underlayer and the total sputtering gas pressure.

Alternate layer deposition method for the deposition of c-axis oriented hexagonal barium ferrite thin films

Sputter-deposition of c-axis perpendicularly oriented hexagonal barium ferrite (BaM: BaFe 12O 19, and BaW: BaFe 18O 27) thin films was attempted by means of an alternate periodic deposition of Fe 3O 4 layer (S-layer) and BaFe 6O 11 layer (R-layer). BaM film with c-axis orientation was obtained at temperatures above 540 C, in which control of the thickness of both S-layer and R-layer was very important to obtain a BaM thin film with c-axis orientation. BaW film, however, was not obtained at the periodic layer deposition condition corresponding to the BaW crystal ( S-layer= 9.3 Å,R-layer= 6.9 Å).

Preparation of c-axis Oriented Hexagonal Barium Ferrite Thin Films by Alternate Layer Deposition Method

Preparation of c-axis Oriented Hexagonal Barium Ferrite Thin Films by Alternate Layer Deposition Method

Structure and magnetic properties of hexagonal barium ferrite films deposited by alternate layer deposition method

Deposition of c-axis perpendicularly oriented hexagonal barium ferrite thin films were formed by an alternate periodic deposition of S (Fe6O8) and R(BaFe6O11) layers. BaM film with excellent c-axis orientation and good crystallinity was obtained when S layers 4.7 A thick and Rlayers 6.9 A thick was deposited on a ZnO underlayer. To reduce the amount of the Zn ions diffusing from the ZnO underlayer to the BaM film, the thickness of the ZnO underlayer was reduced. An underlayer less than 10 nm thick, however, significantly degraded the c-axis orientation of the BaM films. We also tried to deposit BaM films on various kinds of underlayers such as α-Fe2O3 and amorphous barium ferrite (a-BaM). A BaM film with c-axis orientation was obtained only on a ZnO underlayer and an a-BaM/ZnO underlayer, although the c-axis of the BaM crystallites in the film deposited on a ZnO underlayer inclined about 2 degrees from the normal to the film surface.

Control of orientation and crystallite size of barium ferrite thin films in sputter deposition

Hexagonal barium ferrite thin films were deposited in a facing target sputtering system. Films with random orientation, and c-axis orientation were obtained by depositing the films on a thermally oxidized silicon wafer and on a c-axis oriented ZnO underlayer, respectively. The film deposited on the thermally oxidized silicon wafer had crystallite sizes as large as 1500 /spl Aring/, which was increased to about 2000 /spl Aring/ by depositing the film on the substrate with ZnO underlayer. The randomly oriented film had a large coercive force of about 4000 Oe and exhibited almost isotropic properties. In contrast, the c-axis oriented film deposited on ZnO underlayer had a large perpendicular magnetic anisotropy field above 10 kOe and exhibited an angular dependence of coercivity consistent with a fanning model, although the film had a smaller coercive force and smaller saturation magnetization. A strong negative magnetic interaction operated between the particles in the perpendicular direction of the film. These BaM films had a large dispersion in coercivity even in the film with excellent c-axis orientation (/spl Delta//spl theta//sub 50/=1.6/spl deg/).

Oxygen pressure dependence of laser deposited barium ferrite films on LLC(111)

Hexagonal Barium Ferrite thin films with perpendicular anisotropy were successfully fabricated on the (111) surface of large lattice constant (LLC) garnet substrates using pulsed laser deposition. Oxygen pressure plays a crucial role in determining film growth characteristics. The film grown at 50 mTorr oxygen pressure has a clear hexagonal structure but is very weakly crystallized due to the lack of oxygen. Increasing the oxygen pressure enhances both crystallization and the in-plane c-axis oriented crystal growth, hence it reduces the perpendicular anisotropy. The optimum pressure is about 180 mTorr which gives a crystallized film with predominantly perpendicular c-axis orientation. The sensitive dependence of film structure on processing gas pressure shown in this work is important in controlling film properties such as anisotropy and grain size for different applications.