Development and Applications of Nanostructured Soft Magnetic Cores with Extremely Low Loss and Controlled Permeability

通过这一研究项目，开发出了一种磁导率可控、磁损耗极低的新材料。该材料是由非晶态Fe-Nb-Si-B薄带在拉应力作用下晶化而成。张应力作用下的晶化产生了垂直于带状轴的磁各向异性，并导致了直到磁饱和的线性磁化曲线。由于各向异性的大小与应力值成正比，因此通过改变外加应力的大小可以很容易地控制渗透率。在该方法中，通过焦耳加热移动的非晶薄带的连续晶化，使我们能够在移动速度超过200 cm/min的情况下制备出磁导率可控的薄带。由于各向异性的发展可以在不到1s的极短时间内完成，因此通过改进结晶装置，有望在更快的移动速度下连续结晶。当直径大于由饱和磁致伸缩、杨氏模数和带材厚度确定的临界值时，所制备的磁芯表现出良好的软磁性能，反映了带材的磁性。岩心的磁导率可以控制在几百个值，并在2 MHz以下保持恒定。所得磁芯的磁损耗为铁氧体磁芯的1/3。在不降低磁性能的情况下，磁芯适用的直流偏置磁场是铁氧体磁芯的3倍，这可以归因于所开发的材料具有较大的饱和磁化强度。

A new material with controllable permeability and extremely low magnetic loss was developed through this research project. The material was prepared by the crystallization of an amorphous Fe-Nb-Si-B ribbon under tensile stress. The crystallization under tensile stress induced magnetic anisotropy perpendicular to the ribbon axis, and resulted in the linear magnetization curve up to magnetic saturation. As the magnitude of the anisotropy was proportional to the stress value, the permeability was controlled easily by changing the magnitude of the applied stress.The crystallization under tensile stress was achieved by several annealing methods. In the methods, the continuous crystallization of a moving amorphous ribbon by Joule-heating enabled us to prepare a ribbon with controlled permeability under the moving velocity exceeding 200cm/min. As the development of the anisotropy can be completed in an extremely short time less than 1 sec, the continuous crystallization under a faster moving velocity is expected by improving apparatus for crystallization.Toroidal cores were obtained from a developed ribbon, and their magnetic properties were evaluated at the frequencies up to 2MHz. The prepared cores exhibited superior soft magnetic properties reflecting the magnetic properties of the ribbon, when their diameters were larger than a critical value which was determined from the saturation magnetostriction, Young modulus, and the thickness of the ribbon. Permeability of a core could be controlled at a value of a several hundreds and was constant up to 2MHz. Magnetic loss of the obtained cores was 1/3 of that of a ferrite core. The DC-bias filed applicable to the cores without deterioration of magnetic properties was 3 times as large as that of a ferrite core, which can be attributed to the large saturation magnetization of the developed material.