磁，是一种非常普遍的现象，我们的日常生活中随处可见。从电子设备、电力系统到通讯自动化控制，无处不利用到磁效应和磁性材料。而随着磁技术的发展，其应范围更扩展到生物科学、农林业科学乃至新兴的环境科学等领域中。众所周知，煤在工农业生产所用燃料中占有相当大的比例 Magnetism is a very common phenomenon that can be found everywhere in our daily life. From electronic equipment, power systems to communications automation control, ubiquitous use of magnetic effects and magnetic materials. With the development of magnetic technology, its scope should be extended to biological sciences, agroforestry and even emerging fields of environmental science. It is well known that coal accounts for a considerable proportion of the fuel used in industrial and agricultural production