Magnetic properties of semiconductors and substrates beyond diamagnetism studied by superconducting quantum interference device magnetometry
The superconducting quantum interference device (SQUID) magnetometer is one of the most sensitive experimental techniques to magnetically characterize samples with high sensitivity. In cases where thin films on substrates are studied great care has to be exercised to subtract the diamagnetic response of the substrate, in particular, if the magnetization is measured in different orientations. Here it will be shown that the assumption of an isotropic, temperature-independent diamagnetism is only a first approximation. One has to consider anisotropic contributions to the diamagnetism in anisotropic crystals such as sapphire as well as temperature-dependent van Vleck-like components in semiconductor substrates such as GaAs or Si. When great care is exercised it becomes feasible to measure, for example, the anisotropic paramagnetic properties of thin films of dilute magnetic semiconductors (DMS) using SQUID. This will be illustrated by measurements of the DMS Co-doped ZnO.