介绍了铁磁性物质静置于地磁场中产生的自发磁化和退磁的原因, 主要有以下三点: 一是磁时效——铁磁性物质的磁性和磁畴的空间排列都滞后于施加于其上的磁化场; 二是地磁场强度大小和方向随着时间推移而发生的周期性变化; 三是金属的时效——材料中机械应力随着时间流逝导致其磁化曲线和金相组织的改变以及延迟裂纹的出现等。

The reasons causing the spontaneous magnetization and demagnetization of ferromagnetic materials staying in static state in the geomagnetic field are explained in the present paper. The first cause is the magnetic ageing——the magnetism of ferromagnetic materials and the spatial arrangements of magnetic domains all lag behind the magnetizing field applied upon them. The second one is periodical changes of the geomagnetic field strength in magnitudes and directions with the passage of time. And the final cause is the ageing of metals——the increasing of mechanical stress in the materials versus time induces the change of its magnetization curve and metallographic constitutional changes as well as the appearance of the delayed cracking etc.