Local Magnetic Imaging of Epitaxial Magnetic Insulator on Semiconductor Nanowire*

The observation of properties related to Majorana bound states in indium arsenide (InAs) nanowire-epitaxial aluminum hybrid structure has been encouraging, but the need for a large external magnetic field makes their control and application very challenging. To locally introduce a magnetic exchange field, a single-crystalline ferromagnetic insulator europium sulfide (EuS) has been grown directly onto the InAs nanowire. Using a scanning Superconducting QUantum Interference Device (SQUID) microscope, we study the local magnetization and susceptibility of the hybrid magnetic structure on a sub-micron scale. Imaging local magnetic properties as a function of temperature and external field on multiple devices allow us to characterize homogeneity, anisotropy and domain formation, which will be crucial to further develop these topological superconducting devices.