H. Casalta et al., Direct measurement of superparamagnetic fluctuations in monodomain Fe particles via neutron spin-echo spectroscopy, PHYS REV L, 82(6), 1999, pp. 1301-1304
Using the technique of neutron spin-echo spectroscopy, we have conducted a
direct measurement of the superparamagnetic relaxation of nanoscale, magnet
ic monodomain iron particles in the time range between 0.01 and 160 nsec an
d for momentum transfers q between 0.035 and 0.15 Angstrom(-1) Using a phen
omenological model which includes the effect of a particle size distributio
n, we are able to determine the temperature T and q dependence of the longi
tudinal superspin relaxation time spanning 4 orders of magnitude. We find t
hat for T less than or similar to 40 K, interparticle correlations affect t
he longitudinal superspin Fluctuations. [S0031-9007(98)08356-2].