 
Summary: Sensing magnetic fields using superparamagnetic nanomagnets
R. P. Cowburn,a)
D. K. Koltsov, A. O. Adeyeye, and M. E. Welland
Nanoscale Science Laboratory, Department of Engineering, University of Cambridge, Trumpington Street,
Cambridge CB2 1PZ, United Kingdom
An experimental investigation using magnetooptical magnetometry is described into the dependence
of susceptibility and hysteresis on the lateral size 30500 nm , thickness 37.5 nm , and
geometric shape triangular, square, and pentagonal of supermalloy nanomagnets made by electron
beam lithography. We show that as the lateral size of the nanomagnets is reduced, magnetic softness
is at first reduced and then increases abruptly. We show that this increase in softness is due to
thermal fluctuations overcoming the anisotropy imposed by the geometric shape of the
nanomagnets, leading to superparamagnetism. Nanometer scale magnetic elements with high
susceptibility, zero hysteresis, and saturation fields of a few oersteds can thus be made. Implications
for field sensing technology are discussed. © 2000 American Institute of Physics.
S00218979 00 351088
INTRODUCTION
Advances in high resolution lithography now mean that
it is possible to make zerodimensional nanomagnets in
which all three dimensions are constrained on the nanometer
scale.1
