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.