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在100～300 K温区内,用30 MHz频率的超声对Nd_(15.8)Fe_(18.4)B_(5.8)磁体进行了纵波和横波的声速及声衰减测量。发现对应于自旋再取向温度、声速及声波衰减均发生突变,其转变温度为132 K。从自由能角度,在理论上阐述了声波与发生自旋再取向的关系。发现自旋间交换能的变化,对自旋再取向起着关键作用。由超声波衰减变化的振荡特性,推知自旋偏转的量子性,即每个自旋偏转的数值和偏转了的自旋数目并不是温度的连续函数。自旋再取向具有持续性。
In the temperature range of 100 ~ 300 K, the sound velocity and sound attenuation of the longitudinal and transverse waves of the Nd_ (15.8) Fe_ (18.4) B_ (5.8) magnet were measured by the ultrasonic frequency of 30 MHz. It was found that corresponding to the spin reorientation temperature, both the sound velocity and acoustic attenuation were abrupt changes, the transition temperature of 132 K. From the perspective of free energy, the relationship between acoustic wave and spin reorientation is theoretically expounded. It is found that the change of the exchange energy between the spins plays a key role in the spin reorientation. From the oscillatory characteristics of ultrasonic decay variation, we infer the quantum nature of spin-deflection, that is, the value of each spin-spin and the number of deflected spin-numbers are not continuous functions of temperature. Spin reorientation is persistent.