用压电晶片法研究铁在稳定磁场中作横振动时的声频内耗

用罗谢耳盐(NaKC₄H₄O₆·4H₂O)压电晶片测量铁在稳定磁场中作横振动时的内耗,所用的振动频率是1633周/秒。当磁场强度小於40—50奥时,内耗随着磁场强度而变化的曲线几乎是平的,其后则变化较快,在超过约150奥时,内耗的变化又渐越平缓,最后达到一个差不多恒定的最大值。这个内耗最大值在饱和磁场强度下并不降低,这种现象是以前所没有观察到的。根据初步的分析,认为所观察到的内耗舆铁磁性物质在磁场中作横振动时磁畴的磁化向量的转动有密切关系。铁中的磁畴的磁化向量由於试样的弯曲而随着转向,但是外加磁场的作用却要使它们转囘到舆磁场方向一致。通过磁致伸缩的作用,磁畴的转动引起试样的附加应变。这种磁性现象舆弹性现象之间的耦合过程需要一定的时间,因而造成一种应变落后於应力的情况,在周期性应力的作用下便引起内耗。

A STUDY ON THE ACOUSTIC INTERNAL FRICTION OF IRON VIBRATING TRANSVERSELY IN A STEADY MAGNETIC FIELD BY PIEZO-ELECTRIC CRYSTAL PLATES

The acoustic internal friction of iron vibrating transversely in a steady magnetic held was measured by means of Rochelle salt (NaKC₄H₄O₆·4H₂O) crystal plates, the frequency of vibration used was 1633 cycles/sec. When the strength of the magnetizing field is lower than 40-50 oersteds, the curve showing the dependence of internal friction on magnetic field strength is almost flat, and becomes steeper for a higher field strength. However, as the field intensity exceeds 150 oersteds or so, the change of internal friction with field strength becomes slower again, and finally approaches to a maximum value. This maximum value of internal friction does not decrease under a saturation magnetic field. Such a phenomenon has not been observed before.According to a preliminary analysis, the observed internal friction may possibly be associated with the rotation of the magnetization vector of the magnetic domains in iron vibrating transversely in a steady magnetic field. The magnetization vector of the magnetic domains is turned because of the bending of the specimen. The action of the magnetizing field, however, tends, to turn the magnetization vector back so as to be parallel with the field direction. Through magnetostriction, the rotation of the magnetization vector induces an auxiliary strain in the specimen. A definite amount of time is required in the process of the coupling between the magnetic and elastic phenomena. This creats a condition for which the strain lags behind the stress, and gives rise to internal friction under periodic stress.