J. Weissmuller et al., Analysis of the small-angle neutron scattering of nanocrystalline ferromagnets using a micromagnetics model - art. no. 214414, PHYS REV B, 6321(21), 2001, pp. 4414
In ferromagnets with a nonuniform magnetocrystalline and/or magnetoelastic
anisotropy, such as nanocrystalline (nc-) or cold-worked (cw-) polycrystall
ine materials, the static magnetic microstructure gives rise to strong elas
tic magnetic small-angle neutron scattering (SANS). The paper explores a me
thod for analyzing field-dependent SANS data from such materials in terms o
f a model based on the theory of micromagnetics. Samples of cw Ni and of el
ectrodeposited nc Ni and nc Co were characterized by x-ray scattering and m
agnetometry, and were investigated by SANS both with and without polarizati
on of the neutron beam. The variation of the differential scattering cross
section with the scattering vector and with the applied magnetic held is we
ll described by the model. Also, experimental results for the exchange stif
fness constant A and for the spin-wave stiffness constant D obtained from t
he analysis are found to agree with literature data obtained by inelastic n
eutron scattering on single-crystal specimens, The model supplies an ''anis
otropy field scattering function" that contains information on the magnitud
e of the magnetic anisotropy in the material, and on the characteristic len
gth scales on which the anisotropy changes direction. The results suggest t
hat the anisotropy may be strongly nonuniform in each crystallite, possibly
due to twinning, and that some magnetic moments in the Ni samples are stro
ngly pinned at defects.