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高性能永磁体的需求。纳米复合磁体就是这样一种候选材料，有望呈现出更高的能量产物。本课题研究了Nd-Fe-B薄膜的制备。研究了在不同条件下制备的薄膜的磁性能和微观结构。以钨丝为热源，采用闪蒸法在玻璃衬底上制备薄膜。将均匀化的Nd_<2.1> Fe_<14> B合金粉碎成粉末，进行真空沉积。采用图像炉进行沉积后热处理。采用XRD、SEM-EDX和AES对膜的微观结构进行了表征，并用VSM对膜的磁性能进行了测试。制备的薄膜未经沉积后热处理，由于没有观察到XRD峰，所以呈无定形。虽然热处理有效地使薄膜结晶，但它引入了许多裂纹，这些裂纹是由衬底材料和薄膜之间的热膨胀差异引起的。这些裂纹会导致薄膜内部氧化。在薄膜表面涂覆几种不同的材料，结果发现Ti涂层在防止裂纹和氧化方面最有效。由于闪蒸沉积后膜中硼含量极低，热处理后出现Nd_2Fe_<17>相，而不是原始钢锭的主要相Nd_2Fe_<14>B。硼含量的下降是由于与钨丝的反应，钨丝被用作沉积的热源。然而，在衬底上预涂细硼粉是补偿硼损失的有效方法。当衬底温度低于500℃时，形成非晶态Fe和Nd相，而当温度高于650℃时，形成Nd_2Fe_<14>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.