A new development in small-angle neutron scattering with polarization analysis allows us to directly extract the average spatial distributions of magnetic moments and their correlations with threedimensional directional sensitivity in any magnetic field. Applied to a collection of spherical magnetite nanoparticles 9.0 nm in diameter, this enhanced method reveals uniformly canted, magnetically active shells in a nominally saturating field of 1.2 T. The shell thickness depends on temperature, and it disappears altogether when the external field is removed, confirming that these canted nanoparticle shells are magnetic, rather than structural, in origin.

AbrlracL Muon spin relaxation (0s) aperimenu were mrried out in zero field on polycrystalline samples of Hf2Co and HfiCoHs. In lhe unhydrided alloy the muon preferentially oacupies Octahedral intess1iee-s and diEuses through a tunnelling mechanism within lhe network made oi adjacent octahedra above PO K In mnlrast, the muon -pies lelrahedral inlemtices in the hydrided alloy. Muon diffusion takes place through two distinct phonon-assisted tunnelling mechanisms wilh a possible contribution of overbarrier hopping above 250 & and appears lo be slrongly enhaneed by the presence of hydrogen. This eEed b attribuled U) the different pathways taken bj the muon in hydrided and unhydrided Hf2Co. A comparison with llie hydrogen jump rate measured by pwlurbed angular correlation in the same hydride provides confirmation that the hydrogen mobility is indeed faster than that of the muon, which appears lo be a quite general result in concentrated metallic hydrides.

Muon diffusion studies have been performed in the fcc metals Pt, Pd and Pb. The muons start to diffuse above 100 K in Pt, while they appear to be mobile at all temperatures down to 15 K in Pd. The data on Pb suggest mobility above T = 30 K. These new data extend the range of fcc metals available for systematic comparisons of muon diffusion.

Small-angle neutron scattering with polarization analysis reveals that Fe 3 O 4 nanoparticles with 90 Å diameters have ferrimagnetic moments significantly reduced from that of bulk Fe 3 O 4 at 10 K, nominal saturation. Combined with previous results for an equivalent applied field at 200 K, a core-disordered shell picture of a spatially reduced ferrimagnetic core emerges, even well below the bulk blocking temperature. Zero-field cooling suggests that this magnetic morphology may be intrinsic to the nanoparticle, rather than field induced, at 10 K.

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