Low-temperature magnetization dymanics of TM-Al-O (TM=Fe and Co) granular magnetic films

研制了一台用于外磁场下低温布里渊光散射研究的闭式循环制冷机。我们还提高了我们的BLS装置的性能，为长时间的频谱积累。利用这些装置，我们成功地观察到Co-Al-O薄膜在300 - 15 K温度范围内，在2.0 - 4.5kOe磁场下的超顺磁（SPM）激发的散射，并建立了SPM BLS谱的理论模型。我们可以用理论模型分析观测到的光谱。在150 K附近发现了峰频率和峰宽的反常温度行为。这种异常的行为可以归因于一个分散效应，由于一个低的激活能和一个快速的弛豫时间的顺序为10 ps的粒子磁化和弛豫的进动之间的耦合。我们正在计划广泛的BLS研究的自旋波从铁磁薄膜在低温下的磁场。

We prepared a closed-cycle refrigerator for low-temperature Brillouin light scattering (BLS) study under external magnetic fields. We also improved the performances of our BLS apparutus for long spectrum-accumulation. With these apparutus we successfully observed scattering from super-paramagnetic (SPM) excitations for Co-Al-O films in a temparture range of between 300K and 15K under magetic fields of between 2.0kOe and 4.5 kOe.We developed a theoretical model for SPM BLS spectrum. We could analyze the observed spectra with the theoretical model. We found an anomalous temperature behavior of the peak frequency and width at around 150 K. This anomalous behavior can be attributed to a dispersion effect due to a coupling between precession of particle magnetization and relaxation with a low activation energy and a fast relaxation time of an order of 10 ps.We are planning extensive BLS studies of spin waves from ferromagentic thin films at low temperatures under magnetic fields.