High sensitivity SQUID magnetometer / AC susceptometer

磁矩和磁化率等磁性参数在磁性材料的研究和表征中起着基础性的作用。利用本文所用的SQUID磁强计，研究了磁性薄膜、磁性异质结构、磁团簇或分子磁体系综以及超导层的磁特性。在此设想的研究工作的一个重要部分是针对具有亚铁磁性或反铁磁性的样品。这些样品通常具有非常小的(净)磁矩，这只能用高灵敏度的最先进的磁力计来解决。更具体地说，我们希望使用磁测量来定量研究磁矩作为磁场强度、磁场取向和温度的函数的演化。除了量化饱和磁矩、剩磁磁矩和矫顽场外，这些实验还对样品的磁化反转过程和磁各向异性提供了重要的见解。关于这些磁性的详细知识对于优化样品制备过程以及分析和解释在其他实验中获得的测量数据是重要的。此外，我们希望利用在同一装置中同时记录同一样品的磁输运和磁化数据的可能性，以研究磁性和磁阻响应之间的相互作用，例如在磁铁矿的Verwey相变中，或者在铁磁和反铁磁体中的反常或拓扑霍尔效应中。最后，除了磁测量之外，我们还打算使用交流磁化率测量来量化磁有序温度以及不同磁相的存在和范围。由于磁化率的虚部与磁耗散直接相关，交流磁化率测量也可以为分析磁波动现象提供重要信息，目前康斯坦茨大学的几个小组正在研究这一现象。

Magnetic parameters such as the magnetic moment and the magnetic susceptibility play a fundamental role in the study and characterization of magnetic materials. With the SQUID magnetometer applied for here, the magnetic properties of thin magnetic films and magnetic heterostructures, ensembles of magnetic clusters or molecular magnets, as well as superconducting layers shall be investigated. An important part of the research work envisaged hereby aims at samples with ferrimagnetic or antiferromagnetic properties. These samples typically feature very small (net) magnetic moments, which can only be resolved with a highly sensitive, state-of-the-art magnetometer. More specifically, we want to use magnetometry measurements to quantitatively study the evolution of the magnetic moment as a function of magnetic field strength, magnetic field orientation and temperature. In addition to quantifying the saturation moment, the remanent moment and the magnetic coercive fields, such experiments also provide important insights into the magnetization reversal process and the magnetic anisotropy of the samples. Detailed knowledge about these magnetic properties is important for optimizing sample preparation processes, and for analyzing and interpreting measurement data acquired in other experiments. In addition, we want to use the possibility of recording magnetotransport and magnetization data simultaneously in one and the same sample in one and the same setup, in order to investigate the interplay between magnetic properties and magnetoresistive response, e.g. in the Verwey transition in magnetite, or in the anomalous or topological Hall effect in ferromagnets and antiferromagnets. Finally, in addition to magnetometry, we intend to use AC magnetic susceptibility measurements to quantify magnetic ordering temperatures and the existence and range of different magnetic phases. Since the imaginary part of the susceptibility is directly linked to magnetic dissipation, AC susceptibility measurements can also provide important information for the analysis of magnetic fluctuation phenomena, which currently are being studied by several groups within at the University of Konstanz.