Preparation of magnetic films by new technique "ultrasound enhanced" ferrite plating

研究人员发明的铁氧体电镀使铁氧体膜从水溶液中形成。由于不需要热处理，铁氧体电镀便于使用非耐热物质（如塑料、纳米多层材料等）作为衬底制造铁氧体薄膜器件。在本研究中，我们将铁氧体电镀与声化学技术相结合，以改善镀层的结晶度和磁性能。用功率超声波（19.5kHz, 600W）对70℃的FeCl_2水溶液进行超声处理，成功地将平均直径为0.25和4.5 μ m的聚丙烯酸酯球包覆在磁铁矿-磁铁矿混合溶液的铁氧体涂层上。这打破了之前被封装颗粒尺寸的下限（0.3 μ m）；如果没有超声波的作用，铁氧体涂层会变得不连续或孤立。高频超声（1.6MHz, 20W）和低频超声同时作用，Fe_3O_4薄膜的表面光滑度得到改善，Ni离子在NiZn铁氧体（Ni_<3-x-y> Ni_x Zn_y O_4）薄膜中的溶解度由x=0.35提高到0.42。明显的改善是由于超声水溶液中空化气泡破裂引起的“热点”和“微搅拌”。

Ferrite plating invented by the investigators enables formation of ferrite films from aqueous solution. Requiring no heat treatment, the ferrite plating facilitates fabrication of ferrite film devices using non-heat-resistant substances (e.g.plastics, nano-sized multilayrs, etc.) as substrates. In this study we combined the ferrite plating with sonochemical technology to improve the crystallinity and magnetic properties of the plated films. Applying power ultrasound waves (19.5kHz, 600W) to an FeCl_2 aqueous solution at 70ﾟC,we successfully encapsulated polyacrylate spheres of two sizes, 0.25 mum and 4.5mum in average diameter, with ferrite coatings of a magnetite-maghemite mixed solution. This broke the previous lower limit (0.3mum) of the size of the particles to be encapsulated ; without application of the ultrasound waves, the ferrite coating became discontinuous or insular. Applying high frequency ultrasound waves (1.6MHz, 20W) and the above low frequency ultrasound waves simultaneously, Fe_3O_4 films were successfully improved in surface smoothness and solubility limit of Ni ions in films of NiZn ferrite (Ni_<3-x-y> Ni_x Zn_y O_4) was increased from x=0.35 to 0.42. The marked improvements are ascribed to "hot spots" and "micro-stirring" caused by collapse of cavitation bubbles in the sonicated aqueous solution.