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Brillouin spectroscopy of spin waves in metallic ferromagnetic crystals

金属铁磁晶体中自旋波的布里渊光谱

基本信息

批准号：
09440142
负责人：
YOSHIHARA Akira
金额：
$ 7.42万
依托单位：
Ishinomaki Senshu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09440142/
关键词：
Brillouin scattering spin wave EuS phase transition demagnetization Fe Au superlattice exchange coupling anisotropy EuS Au人工格子膜交換相互作用

项目摘要

In this research project we have investigated thermally excited spin waves in various metallic ferromagnetic crystals by means of Brillouin light scattering (BLS).In the first year of our project we have examined spin waves of a typical ferromagnetic semiconductor EuS single crystal in a wide temperature range between 7.5 K and 300 K including the ferromagnetic transition temperature at 16.5 K.We could observe magnetic scattering even at room temperature which is far above the transition temperature. However we could observe neither softeing of the spin wave frequency nor broadening of peak width around the transition temperature. We found that the spin wave frequencies in the ferromagnetic phase are much lower than the values evaluated from the magnetization of EuS and the applied magnetic field. This observation strongly indicates that the demagnetization coefficient near the surface illuminated by laser beam is much less than the value of 4p which is expected for a thin film. In order to clarify the demagnetization coefficient effect, we are planning a new BLS study of sputtered EuO thin films which also undergo a very similar ferromagnetic phase transition.In the second year we have mainly investigated the interlayer exchange coupling phenomena of MBE prepared fine-layered Fe (n ML)/Au (n ML) (n=1 to 5) superlattices which can be regarded as regularly ordered Fe-Au alloy single crystals with D_<4h> tetragonal sysmetry. We have studied spin waves for both of integer and non-integer atomic layer superlattices. We found that the interlayer exchange coupling between the Fe layers across the Au layers is always ferromagnetic for our superlattices and becomes very weak around at 3 ML and 5 ML.This is the first observation of such even-odd effect of the interlayer exchange coupling phenomena in superlattice structures.

在本研究计划中，我们利用布里渊光散射（BLS）研究了各种金属铁磁晶体中的热激发自旋波在我们项目的第一年，我们研究了典型铁磁半导体EuS单晶在7.5 K和300 K之间的宽温度范围内的自旋波，包括16.5 K的铁磁转变温度，我们可以观察到磁散射。即使在远高于转变温度的室温下也是如此。然而，我们既没有观察到软化的自旋波频率，也没有加宽的峰宽附近的转变温度。我们发现，在铁磁相的自旋波频率远低于从EuS的磁化强度和施加的磁场的值。这一观察结果强烈地表明，在激光束照射的表面附近的退磁系数远小于对于薄膜所期望的4p值。第二年，我们主要研究了分子束外延制备的Fe（nML）/Au（nML）（n=1 ~ 5）超晶格的层间交换耦合现象，这些超晶格可以看作是具有D_四对称性的规则有序的Fe-Au合金单晶<4h>。我们研究了整数和非整数原子层超晶格的自旋波。我们发现，对于我们的超晶格结构，Fe层和Au层之间的层间交换耦合始终是铁磁的，并且在3 ML和5 ML附近变得很弱，这是首次在超晶格结构中观察到这种层间交换耦合现象的奇偶效应。