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重要作用。利用SQUID磁强计，可以研究磁性薄膜和磁性异质结构、磁性团簇或分子磁体的集合体以及超导层的磁性。因此，设想的研究工作的一个重要部分是针对具有亚铁磁或反铁磁特性的样品。这些样品通常具有非常小的（净）磁矩，只能用高灵敏度的最先进的磁力计来解决。更具体地说，我们希望使用磁力测量来定量研究磁矩随磁场强度、磁场方向和温度的变化。除了量化的饱和力矩，reflectance矩和矫顽磁场，这样的实验也提供了重要的见解的磁化反转过程和样品的磁各向异性。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非常重要。此外，我们希望使用的可能性，同时记录磁输运和磁化数据在一个和同一个样品在一个和相同的设置，为了研究磁性能和磁阻响应之间的相互作用，例如在磁铁矿的Verwey过渡，或在铁磁体和反铁磁体的异常或拓扑霍尔效应。最后，除了磁力测量，我们打算使用交流磁化率测量来量化磁有序温度和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磁波动现象的分析提供重要信息，目前康斯坦茨大学的几个小组正在研究磁波动现象。

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.