FIELD-DEPENDENT MICROSUSCEPTOMETRY ON MAGNETIC CRYSTALLITES WITH INTEGRATED DC SQUID

We report the use of unshielded planar low-T-c de SQUIDs for temperatu re-dependent ac and de magnetic susceptibility measurements on small p articles in magnetic fields of up to 300 G. These measurements were ma de with integrated microsusceptometers which can operate in such field s when applied in the plane of the device. We show paramagnetic, antif erromagnetic, and superconducting behavior on various samples of order 20-50 mu m from 0.3 to 4 K and discuss the effect of sample placement on the magnitude of the signal. (C) 1998 American Institute of Physic s.