Abstract Effect of an external magnetic field on the sound attenuation coefficient is investigated using the Landau-Ginzburg model incorporating a tricritical to mean-field crossover. The dynamics is treated within the framework of the Onsager theory. Temperature variation of the attenuation coefficient has been obtained for arbitrary values of the magnetic field. For non-zero sixth order term in the Landau-Ginzburg expansion and for sufficiently high magnetic field the maximum in attenuation occurs above the Curie point and is displaced towards the higher temperatures as the magnetic field is increased. In the high temperature region a very rapid increase of attenuation with reduced temperature is demonstrated before the maximum is attained. This increase is much steeper than in the analogous hydrodynamic regime below the Curie temperature. At constant temperature the quadratic field dependence of attenuation on magnetic field is found in the low-field region until a maximum at a certain magnetic field is attained. This maximum is followed by a power-law decay to zero in the high-field region. A quantitative comparison between obtained results and available ultrasonic measurements in MnP is presented. Good agreement is achieved for moderate and large magnetic fields and temperatures not very close to the Curie temperature.

中文翻译：

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外加磁场下铁磁体中的超声波衰减

摘要 使用包含三临界到平均场交叉的 Landau-Ginzburg 模型研究了外部磁场对声衰减系数的影响。在 Onsager 理论的框架内处理动力学。已经获得了磁场的任意值的衰减系数的温度变化。对于 Landau-Ginzburg 膨胀中的非零六阶项和足够高的磁场，衰减的最大值出现在居里点上方，并随着磁场的增加而向更高的温度移动。在高温区域，在达到最大值之前，随着温度降低，衰减会非常迅速地增加。这种增加比居里温度以下的类似流体动力学状态要陡峭得多。在恒定温度下，在低场区域中发现衰减对磁场的二次场依赖性，直到在某个磁场处达到最大值。该最大值之后是高场区域中的幂律衰减至零。介绍了获得的结果与 MnP 中可用的超声波测量值之间的定量比较。对于不太接近居里温度的中等和大磁场和温度实现了良好的一致性。