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We investigate the spatial distribution of spin orientation in magneticnanoparticles consisting of hard and soft magnetic layers. The nanoparticlesare synthesized in a core / shell spherical morphology where the magneticallyhard, high anisotropy layer is CoFe$_2$O$_4$ (CFO) while the lower anisotropymaterial is Fe$_3$O$_4$ (FO). The nanoparticles have a mean diameter of$\sim$9.2 - 9.6 nm and are synthesized as two variants: a conventional hard /soft core / shell structure with a CFO core / FO shell (CFO@FO) and theinverted structure FO core / CFO shell (FO@CFO). High resolution electronmicroscopy confirms the coherent spinel structure across the core / shellboundary in both variants while magnetometry indicates the nanoparticles aresuperparamagnetic at 300 K and develop a considerable anisotropy at reducedtemperatures. Low temperature \textit{M vs. H} loops suggest a multi-stepreversal process. Temperature dependent small angle neutron scattering (SANS)with full polarization analysis reveals a strong perpendicular plane alignmentof the spins near zero field, indicative of spin canting, but the perpendicularalignment quickly disappears upon application of a weak field and little spinordering parallel to the field until the coercive field is reached. Above thecoercive field of the sample, spins orient predominantly along the fielddirection. At both zero field and near saturation, the parallel magnetic SANSpeak coincides with the structural peak, indicating the magnetization isuniform throughout the nanoparticle volume, while near the coercive field theparallel scattering peak shifts to higher momentum transfer (Q), suggestingthat the coherent scattering volume is smaller and likely originates in thesofter Fe$_3$O$_4$ portion of the nanoparticle.

Spin Canting in Exchange Coupled Bi-Magnetic Nanoparticles: Interfacial Effects and Hard / Soft Layer Ordering