Field-dependent microsusceptometry on magnetic crystallites with integrated dc SQUIDs

We report the use of unshielded planar low-Tc dc SQUIDs for temperature-dependent ac and dc magnetic susceptibility measurements on small particles in magnetic fields of up to 300 G. These measurements were made with integrated microsusceptometers which can operate in such fields when applied in the plane of the device. We show paramagnetic, antiferromagnetic, and superconducting behavior on various samples of order 20-50 μm from 0.3 to 4 K and discuss the effect of sample placement on the magnitude of the signal. © 1998 American Institute of Physics.