Electrophoretic Deposition Of Strontium Ferrite Thick Film

The development of communication technology requires microwave devices to become miniaturization, integration and work at high frequency. M-type strontium ferrites(SrM) as a magnetic hexagonal ferrite crystal structure, owing to its high magnetocrystalline anisotropy field, high saturation magnetization, high coercivity as well as good chemical stability, are widely used as perpendicular magnetic recording materials, magnetic and magneto-optical devices and microwave devices. In order to make microwave devices have nonreciprocal characteristics and practical applications, which requires the preparation of a thickness of several tens to hundreds of microns thick ferrite as well as good performance, in this article, SrM ferrite thick films were prepared by electrophoretic deposition.Firstly, a stable SrM ferrite suspension was prepared, It was theoretically considered that in a certain particle size range(r ≤ 20 nm), by adding a surfactant(DBSA) to form a double layer, which can prepare a stable M-type strontium ferrite suspension in a polar solvent(1-butanol). Zeta potential of the suspension was 60 mV, TEM results showed that particles of r ≤ 20 nm can be stably dispersed in 1-butanol, which was consistent with the theoretical calculation.Secondly, the relationship among the mass and thickness of the deposition, the electric field intensity, the electrophoresis time and the electrode distance were investigated theoretically and experimentally. The effect of deposition time on the porosity and densification process had been studied. The results showed that: the mass and thickness increased with the electric field intensity, the deposition time and the distance between the electrodes. But when the deposition time is larger than 15 min, the deposition mass and thickness of the electric field of 40 V/1.5 cm and 60 V/1.5 cm did not increase any more, while 80 V/1.5cm will continue increasing. The thickness of film can reach 40 μm when deposited step by step. The porosity changed with the deposition time, the minimum porosity was obtained when the deposition time was 2 min. The maximum porosity was obtained when the deposition time was 5 min, at this condition the films surface cracked, the porosity will decrease as increasing the electric field. When 1-butanol: xylene = 50:50 vol% homogenous surface morphology can be obtained. The porosity of the film decreased after carrying on densification process in the 1-butanol. The porosity will decrease as time increasing, and a minimum was gained when densification time was 3 min. After that the porosity will rise slowly, The porosity will also decrease as increasing electric field.Finally, The effects of the annealing temperature, the magnetic field orientation and sintering aids(Bi2O3) on the microstructure and magnetic properties of SrM thick films were studied. The results showed that: Excellent properties were obtained when the sintering temperature was 1000 ℃. Under this condition the special saturation magnetization was 45 A?m2/kg with the coercivity 4840 Oe and the remanence ratio 0.5. The remanence ratio can be increased to 0.6 when oriented the thick films under magnetic and electric field in 1-butanol. With the orientation time increased the remanence ratio also improved. When the amount of Bi2O3 was 1.0 wt% the grain size reached the maximum. When the amount of Bi2O3 was 2.0 wt% only more grains growed and presented sintered morphology. When the amount of Bi2O3 was 1.0 wt% the saturation magnetization(4πMs) reaches the maximum of 4300 Gs, the coercive force declined with the increase of the amount of Bi2O3.