Scanning Mutual Inductance Microscope for Magnetic and Superconducting Material Investigations

The performance of superconductors and nanomagnets are often contingent on deliberately nano-patterned structures or inadvertent sub-micron-scale inhomogeneities. Current technology, such as scanning SQUID, is optimized to probe magnetization and susceptibilities at cryogenic temperatures. To obtain spatially-resolved ac magnetic susceptibility, especially in the study of room temperature 2D magnetism and combinatorially synthesized high-Tc superconductors, we propose a scanning mutual inductance microscope (SMIM) that utilizes the nano-positioning mechanism from scanning tunneling microscopy and susceptometry mechanism from two-coil mutual inductance. In this work, we demonstrate with finite element simulation that placing a high magnetic permeability tip at the core of a mutual inductance solenoid can focus kHz-level magnetic field down to sub-micron scales. We discuss the tip design principle, sample measurement geometry, resolution function, and specifically how to obtain the superfluid density for thin film superconductors from such a setup. Finally, experimental demonstrations and limitations will be discussed.