Magnetic field dependent small-angle neutron scattering on a Co nanorod array: evidence for intraparticle spin misalignment

Abstract

The structural and magnetic properties of a cobalt nanorod array have been studied by means of magnetic field dependent small-angle neutron scattering (SANS). Measurement of the unpolarized SANS cross section dAE/d of the saturated sample in the two scattering geometries where the applied magnetic field H is either perpendicular or parallel to the wavevector k i of the incoming neutron beam allows one to separate nuclear from magnetic SANS, without employing the usual sector-averaging procedure. The analysis of the SANS data in the saturated state provides structural parameters (rod radius and centre-tocentre distance) that are in good agreement with results from electron microscopy. Between saturation and the coercive field, a strong field dependence of dAE/d is observed (in both geometries), which cannot be explained using the conventional expression of the magnetic SANS cross section of magnetic nanoparticles in a homogeneous nonmagnetic matrix. The origin of the strong field dependence of dAE/d is believed to be related to intradomain spin misalignment, due to magnetocrystalline and magnetoelastic anisotropies and magnetostatic stray fields.

Small-angle neutron scattering modeling of spin disorder in nanoparticles

“…Günther et al . 16 have suggested the presence of significant intraparticle spin disorder when analyzing SANS experiments on a Co nanorod array: the strong field dependence of that these authors have observed could not be explained by the standard expression for . Likewise, the polarized SANS experiments on ferromagnetic nanowires by Napolskii et al .…”

Magnetic small-angle neutron scattering

“…With typical dimensions of a few tens of nm in cross section, such structures still fit in the framework of nanomaterials (i.e., with two dimensions smaller than ∼ 100 nm). Magnetization reversal in aligned nanowire arrays has been studied using both polarized and unpolarized SANS, and spin misalignment is commonly observed (Grigoryeva et al, 2007;Grutter et al, 2017;Günther et al, 2014;Maurer et al, 2014). However, with a typical nanowire length approaching the micrometer range and usually oriented parallel to the neutron beam, arrays of magnetic nanowires act as a grating, and strong multiple scattering has to be taken into account depending on the nanowire length; this effect is discussed in depth in Grigoriev et al, 2010.…”

“…Due to their relatively large volume, nanowires exhibit stable ferromagnetic properties and are mostly multidomain structures. The particle matrix approach is therefore not applicable to nanowires; indeed, micromagnetic simulations (Vivas et al, 2017) and experimental data (Günther et al, 2014) demonstrate strong deviations from the uniform-particle form-factor model.…”

Exchange bias effect inAu-Fe3O4dumbbell nanoparticles induced by the charge transfer from gold

“…Development of a more realistic two-phase model with polydisperse core-shell building blocks is currently underway. The quality of the SANS fit is ambiguous at higher q, and thus we repeated the small-angle measurements using synchrotron x-rays ( If magnetic interactions between nanoparticles are significant the scattering intensity would depend on the magnitude of an applied magnetic field [54][55][56][57] . We subject the solution of the dumbbell nanoparticles into the magnetic field and found no considerable difference between SAXS intensities measured at 0 and 1.2 T for both samples.…”