Effect of Magnetic Field on Sound Propagation near Magnetic Phase Transition Temperatures
Effect of Magnetic Field on Sound Propagation near Magnetic Phase Transition Temperatures
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磁相变温度附近磁场对声音传播的影响
DOI：
10.1143/ptp.51.1
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发表时间：
1974
期刊：
影响因子：
--
通讯作者：
S. Maekawa
中科院分区：
文献类型：
--
作者：
M. Tachiki;S. Maekawa
对居里和尼尔温度附近自旋临界涨落引起的超声波反常衰减和速度变化进行了理论研究，发现其具有很强的相关性。受施加磁场的影响。在随机相位近似中，衰减系数以两项之和表示；静态自旋极化和双自旋相关函数的交叉项，以及-tw.O~自旋相关函数的乘积。在磁场领域，前一术语具有积极的贡献。衰减，因为只有当静态自旋极化存在时，这项才具有有限值。由于磁场抑制了自旋热波动，后一项在场中减小。这些项的贡献大小取决于温度、磁场强度以及磁性材料中交换相互作用的性质。该理论解释了在磁性材料（包括 MnP、Dy 和 MnF2）中观察到的各种类型的衰减场依赖性。Hirahara 等人最近发现了一个新的衰减峰。基于现有理论解释了磁场下MnP顺磁相的变化。
The anomalous ultrasonic attenuation and velocity variation caused by the critical fluctuation of spins near the Curie and N~el temperatures are theoretically investigated and found to be stronglY:. affected by an application of magnetic field. In the random phase approximation, the attenuation coefficient is expressed in terms of a sum of the two terms; a cross term of the static spin polarizatlpn and th~ two-spin correlation function, and a product of the -tw.O~spin correlation functions. In the :tnagnetic field, the former term has a positive contribution. to the attel\uation, since this term has a finite value only when the static spin polarization exists. The'-latter term decreases in the field, owing to the suppression of spin thermal fluctu;ations due to the magnetic field. The magnitude of the contributions from these terms depends upon temperature, the strength of magnetic field and the nature of the exchange interaction in magnetic materials. The theory explains various types of the field dependence of the attenuation observed in magnetic materials including MnP, Dy and MnF2• A new attenuation peak found recently by Hirahara et al. in the paramagnetic phase of MnP under a magJ~etic field is explained on the basis of the present theory.