Development of Rere-Earth Iron based hard magnetic thin films with high energy products

电子器件小型化的趋势导致了对性能更高的永磁体的需求。纳米复合磁体就是这样一种候选磁体，有望展示更高能量的产品。在本项目中，我们对NdFeB薄膜的制备进行了研究。以钨丝为热源，在玻璃衬底上闪光沉积制备了薄膜，研究了不同工艺条件下制备的薄膜的磁性能和微观结构。将均匀的Nd2.1&Gt；Fe&lt；14&Gt；B合金粉碎成粉末，用于真空沉积。采用成像炉进行沉积后热处理。用X射线衍射仪、扫描电子显微镜和俄歇电子能谱分析了薄膜的微观结构，并用扫描电子显微镜测量了薄膜的磁性能。没有观察到X射线衍射峰，未经沉积后热处理的薄膜呈类非晶态。虽然热处理有效地使薄膜结晶，但它引入了许多裂纹，这些裂纹是由于衬底材料和薄膜之间的热膨胀不同而引起的。这些裂纹可能会导致薄膜内部的氧化。用几种不同的材料在薄膜表面进行了涂层，发现钛涂层对防止裂纹和氧化是最有效的。由于闪速沉积后薄膜中的硼含量极低，热处理后出现了Nd2Fe；lt；17&gt；相，而不是原始钢锭的主相Nd2Fe&lt；14&gt；B。硼含量的降低是由于与用作沉积热源的钨丝发生反应所致。当衬底温度低于500ﾟC时，出现非晶态Fe相和ND相，高于650ﾟC时，出现Nd2Fe&lt；14&gt；B相。

The trend of miniaturizing electronic devices has lead to a demand for higher performance permanent magnets. Nanocomposite magnets are one such candidate, that are anticipated to exhibit higher energy products. In this project, the preparation of Nd-Fe-B thin films has been studied. The magnetic properties and the microstructure of the films prepared under various conditions, have been investigated.Thin films were made on glass substrates by flash deposition, with tungsten wires as the heat source. The homogenized Nd_<2.1> Fe_<14> B alloy was crushed into a powder which was used for vacuum deposition. An image furnace was used for the post-deposition heat treatment. The microstructures of the films were investigated by XRD,SEM-EDX,and AES,and the magnetic properties were measured using a VSM.The films prepared without a post-deposition heat treatment, were amorphous-like in state because no XRD peaks were observed. Although a heat tretment effectively crystallizes the films, it introduces many cracks which are caused by the difference in thermal expansion between the substrate material and the film. These cracks can be lead to oxidation within the films. Coating the surface of the films with several defferent materials was tried, with the result that a Ti coating was found to be most effective in preventing cracks and oxidation.Since the boron content of the films was extremely low after flash deposition, the Nd_2Fe_<17> phase appeared after heat treatment, rather than Nd_2Fe_<14>B which is the main phase of the original ingot. The decrease in boron content is due to a reaction with the tungsten filaments, which are used as the heat source for deposition. However, pre-coating the substrate with fine boron powder was found to be an effective method of compensating for this loss in boron.When the substrate temperatures were below 500ﾟC,amorphous Fe, and Nd phases formed, while the Nd_2Fe_<14>B phase appeared at temperatures above 650ﾟC.