MicroSQUID magnetometry and magnetic imaging

Abstract

We present a new instrument for local magnetization measurements: the micro-Superconducting Quantum Interference Device (microSQUID). The microSQUID consists of a small (∼1 μm diameter) superconducting loop with two microbridge Josephson junctions. The SQUID loop itself serves as the input coil for the magnetic signal. In placing the SQUID very close to the sample, the magnetization measurement of signals as small as 10 000 μ B has been demonstrated. In this limit of close proximity, the spatial resolution of the SQUID is a fraction of the width of the SQUID ring (0.2 μm). We are now building a scanning SQUID microscope. The SQUID is placed by electron beam lithography at the apex of a silicon cantilever. The lever is attached to a force sensor, allowing us to image magnetically, as well as topographically. We expect to obtain a spatial resolution of 50 nm and a flux resolution of about 10 −4 Φ 0. The ensemble is mounted inside an inverted dilution refrigerator. We will discuss the application of this technique to the imaging of vortices in artificial networks.