Dipolar correlations in a nanocomposite: A neutron scattering study of Nanoperm Fe89Zr7B3Cu

We present results for the magnetic-field, temperature, and neutron-polarization dependence of the small-angle neutron scattering intensity in the soft magnetic iron-based nanocomposite Nanoperm (Fe89Zr7B3Cu). An unusual clover-leaf-shaped intensity distribution on the detector is attributed to the dipolar stray fields around the nanosized iron particles, which are embedded in an amorphous magnetic matrix of lesser saturation magnetization. The dipole field induces spin disorder, correlating the spin misalignment of neighboring particles and matrix over several particle spacings. The clover-leaf-shaped anisotropy is observed over a wide range of applied magnetic field and momentum transfer. It persists up to several hundred degrees Kelvin above the Curie temperature of the matrix phase, indicating that some degree of magnetic coupling persists even when the matrix is paramagnetic.