希土离子对高功率铁磁共振的影响

本文利用关联函数方法(久保理论)来讨论高功率下铁磁共振中的非线性过程。对通常的铁磁晶体,目前的理论包含了由H.Suhl所发展起来的半经典理论的结果。对含希土离子的石榴石型铁氧体,给出了希土离子引起的自旋波的频率移动,附加的损耗,以及所谓纵向注入和横向注入的一级二级的非线性过程的临阈场。希土离子的存在使临阈场增大。一般而言,这一关系是很复杂的,但当希土离子含量很少的情形下,对临阈场的影响可归结为自旋波的损耗的增加,临阈场随温度的改变及各向异性完全与低功率下铁磁共振线宽的情况相似。对于现有的一些实验结果,理论作了定性的解释。

THE INFLUENCE OF RARE-EARTH IONS ON THE FERROMAGNETIC RESONANCE AT HIGH POWER LEVELS

The method of correlation function has been utilized to discuss the nonlinear effects in the ferromagnetic resonance at high power levels. For ordinary ferromagnetic crystals, the present theory includes the results of the semiclassical theory developed by H. Suhl as a classical limit. In the case of YIG doped with rare-earth ions, the frequency shift and the additional losses due to the rare-earth ions have been discussed. Besides, the threshold field of the so-called first order process with parallel pumping and the first and second order processes with perpendicular pumping have also been derived. The results obtained show that the rf critical magnetic field increases with the addition of rare-earth ions. In samples with small concentration of rare-earth ions, the influence on the threshold is attributed to the increase of the losses of spin waves. The temperature dependence and the anisotropy of the threshold field are entirely similar to those of the ferromagnetic resonance linewidth at low power level. The experimental results may be satisfactorily explained by the present theory.