  A recent theory [Metlov and Michels, Phys. Rev. B 91, 054404 (2015)] predicts
a qualitatively new effect in the magnetic small-angle neutron scattering
(SANS) cross section of statistically-isotropic disordered ferromagnetic media.
The effect is due to the third-order terms in the amplitude of the
inhomogeneities. Here, its existence is demonstrated both numerically via
large-scale micromagnetic simulations and analyzed experimentally in a
two-phase iron-based nanocomposite. The previous model is extended to an
arbitrary spatial defect profile, which allows us to describe the experimental
field dependence of the third-order SANS effect quantitatively.
