Title :
SQUID microsusceptometry in applied magnetic fields
Author :
Narashimhan, L.R. ; Patel, C.K.N. ; Ketchen, M.B.
Author_Institution :
Dept. of Phys. & Astron., California Univ., Los Angeles, CA, USA
fDate :
6/1/1999 12:00:00 AM
Abstract :
We describe the design and construction of a planar dc SQUID susceptometer to characterize microcrystallites as a function of temperature from 0.3 K to 4 K in magnetic fields exceeding 280 G. Eliminating the need for magnetic shielding permits broader application of SQUIDs to characterization of small spin ensembles. We present temperature- and field-dependent magnetic susceptibility data on crystallites mounted directly on the surface of a SQUID chip. Large, in-plane static fields are applied through an external coil while perpendicular fields up to 2 G can be applied by a series-wound on-chip field coil. Paramagnetic, antiferromagnetic, and superconducting transitions have been resolved on samples of order 20 to 50 /spl mu/m (30 to 500 picomoles, /spl sim/5/spl times/10/sup 16/ emu/Hz/sup 1/2/.) We discuss the effects of sample shape and location on the spin calibration of the assembled susceptometer.
Keywords :
SQUID magnetometers; magnetic field measurement; magnetic susceptibility; 0.3 to 4 K; 20 to 50 micron; SQUID microsusceptometry; antiferromagnetic transitions; applied magnetic fields; field-dependent magnetic susceptibility data; in-plane static fields; microcrystallites; paramagnetic transitions; perpendicular fields; planar dc SQUID susceptometer; sample shape; series-wound on-chip field coil; spin calibration; spin ensembles; superconducting transitions; temperature-dependent magnetic susceptibility data; Antiferromagnetic materials; Crystallization; Magnetic fields; Magnetic shielding; Magnetic susceptibility; Paramagnetic materials; SQUIDs; Shape; Superconducting coils; Temperature;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
