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Barium hexaferrite thin films with thickness of 8 \mu\m had been deposited on a sapphire substrate by radio-frequency magnetron sputtering. The results show that the grain size is about 2 \mu\m in diameter. The coercivity is about 2.2 kOe and the saturation magnetization is about 4000 Gs with remanence ratio of 0.58. Based on the sputtered thin films, a self-biased microstrip junction circulator had been developed. The measured S-parameters indicate that a nonreciprocal effect greater than 10 dB occurs at about 26 GHz. The maximum isolation is 44 dB and the minimum insertion loss is 27 dB. The origins of the large insertion losses have been discussed. [ABSTRACT FROM AUTHOR]

Abstract: M-type barium ferrite thin films were deposited onto sapphire (00 l) substrates by radio frequency magnetron sputtering. An ultra-thin layer about 20nm was deposited and annealed before continuous deposition of the films up to 500nm under different sputtering pressures: 0.2, 0.5, 0.8 and 1.0Pa, respectively. It was found that the atomic ratios of Fe to Ba increased from 9.3 to 15.0 with the increase of the pressure. The films sputtered at all pressures have c-axis normal to the film plane by a four circle X-ray diffractometer, which is an improvement of the films directly sputtered on the substrate. Needle-like grains were formed on the surface of the films under higher sputter pressure with bubble domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops recorded by vibrating sample magnetometer agree with them, where in-plane and out-of-plane loops of the samples prepared under high sputtering pressures are quite different, while they are almost identical of the samples under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the films was increased. Nucleation with c-axis normal to the film plane was deteriorated. Thus samples prepared under high pressure have more needle-like crystallites which have c-axis parallel to the film plane. [ABSTRACT FROM AUTHOR]

Abstract: Hexagonal barium ferrites were deposited onto sapphire substrates by radio frequency magnetron sputtering. The composition, microstructure, and magnetic properties of these isotropic thin films were investigated with Rutherford backscattering spectroscopy, X-ray diffraction, atomic force microscopy, magnetic force microscopy and SQUID magnetometry. The intrinsic coercivity of the films reaches about 11.5kOe at room temperature. The mechanism of the coercivity is proposed to be nucleation in the decoupled single domain nanometer particles as shown by the characteristics of the magnetic domains and the virgin magnetization curves. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Barium ferrite films were prepared by spin-coating of gels on sapphire (00 l) faces. Ethylenediaminetetraacetic acid was used to bind the metal ions. Thin films prepared by this method show faceted hexagonal grains with c-axis normal to the film plane and [110]sapphire ||[100]film. Needle-like grains, which have c-axis in the film plane, are minimized. Epitaxial growth of the film can be observed by the high resolution images. Reduction of the a and c-axis of the film compared with those of the bulk materials is confirmed both in real space and reciprocal space. Magnetic hysteresis loops were recorded in-plane and out-of-plane. The film shows uniaxial anisotropy as exemplified by branched domains with coercivity field of 87.6kA/m along the in-plane direction and of 302.5kA/m along the out-of-plane direction. [Copyright &y& Elsevier]

Abstract: Hexagonal barium ferrite (BaM) thin films have been prepared by sol–gel technique involving spin coating and annealing in air. Different ratios of Ba to Fe, different annealing temperatures and different annealing time are explored. X-ray diffraction shows that the films have been epitaxially grown on the sapphire (001) plane with [100] direction of BaM parallel to [110] of Al2O3, and the c-axes of them being parallel, while magnetic measurements show magnetically anisotropic loops with in-plane and out-of-plane intrinsic coercivity of 87.5kA/m and 230.8kA/m, respectively. [Copyright &y& Elsevier]

Abstract: Hexagonal barium ferrite (BaFe12O19) thin films were fabricated by spin coating of precursors from sol–gel methods. Different amount of citric acid was added. Weight loss and changes of chemical bonds during the heat treatment below 500°C were recorded by thermogravity analyzer and Fourier transform infrared spectroscopy, respectively. The morphology of the films, i.e. the amount of acicular crystallites in the film, was controlled by adjusting the quantity of citric acid. The X-ray diffraction shows that the films are c-axis oriented, but the crystallization is less perfect with the increase of the citric acid. With the increase of the citric acid, the percentage of the acicular crystallites increased. At the same time, the coercivity force increased. The acicular crystallites were not exchange-coupled to the platelet crystallites. The citric acid was understood to form complex with iron ions and accelerate the exothermal auto-combustion. The c-axis oriented growth of the film was thus deteriorated. [ABSTRACT FROM AUTHOR]

Abstract: Barium ferrite thin films have been prepared by radio frequency magnetron sputtering on a sapphire (001) substrate at substrate temperature of 500°C and 650°C, respectively. The films were further annealed in air at 1000°C for 5h. X-ray diffraction shows that the films at the lower substrate temperatures have a good epitaxial relation with respect to the substrate, while the samples under the higher substrate temperatures have (109) planes parallel to the substrate. The remanence ratio decreases from 0.82 to 0.47 when the substrate temperature is increased. We attribute the variation of the growth direction to the enhanced vertical mobility of the deposited atoms when the substrate temperature is increased. [Copyright &y& Elsevier]