  8~nm epsilon-Fe2O3 nanoparticles exhibit a spin reorientation transition that
begins at 150 K which is a hallmark of this unique iron-oxide polymorph. We
find that the change from the high to low temperature magnetic structures has
been suppressed by ~50 K. At the spin reorientation temperature, a change of
the field-dependent response of the tetrahedral sites in intermediate field
strengths (0.25 - 1.5 T) indicates that a collective tetrahedral distortion
occurs to which the octahedral sites adjust, altering the magnetic anisotropy.
An abrupt step in the hyperfine parameters' temperature dependencies,
especially at 125 K for the hyperfine field associated with the Fe4 tetrahedral
sites, suggests strongly a change in the superexchange pathways are responsible
for the spin reorientation.
