Nanoscale Fe particles in an Al 2 O 3 matrix have been investigated by Small-Angle Neutron Scattering (SANS), in addition to SQUID magnetometry and Mossbauer spectroscopy. SANS data analysis indicates an increase of the ferromagnetic correlation length as the temperature decreases, with saturation at roughly the particle size. The amplitude of this scattering decreases with temperature, indicating that it is likely dynamic in origin. There is a second component of the SANS at the smallest wavevector transfers, which we believe arises from inter-particle correlations. The amplitude of this component increases with decreasing temperature, as expected for order parameter scattering.
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Childress et al. (1992) studied this question.