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

本课题开发了一种磁导率可控、磁损耗极低的新型材料。该材料采用非晶态Fe-Nb-Si-B带在拉伸应力下结晶制备。在拉伸应力作用下的结晶引起垂直于磁带轴线的磁各向异性，并导致磁饱和前的线性磁化曲线。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。通过多种退火方法实现了拉伸应力下的结晶。在这些方法中，通过焦耳加热使移动的非晶态带连续结晶，使我们能够在超过200cm/min的移动速度下制备具有可控磁导率的带。由于各向异性的发展可以在不到1秒的极短时间内完成，因此通过改进结晶装置，有望在更快的移动速度下实现连续结晶。从已开发的条带中获得环形磁芯，并在高达2MHz的频率下对其磁性进行了评估。当芯材直径大于饱和磁致伸缩、杨氏模量和带材厚度确定的临界值时，所制备的芯材表现出优异的软磁性能，反映了带材的磁性能。磁芯的磁导率可以控制在几百，并且恒定到2MHz。所得铁芯的磁损失为铁氧体铁芯的1/3。适用于铁氧体铁芯的直流偏置磁场是铁氧体铁芯的3倍，这是由于所制备材料的饱和磁化强度大。

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.