  High resolution electron energy loss spectroscopy (HR-EELS) is utilized to
probe the surface spin canting in nanoparticles of two technologically
important magnetic materials, i.e. Fe3O4 and CoFe2O4 (CFO). A soft experimental
technique is developed that is capable of extracting EELS spectra with one
atomic plane resolution recorded in a single frame. This yields information at
different depth of the nanoparticle from the surface to the core regions with
high signal to noise ratio and without beam damage. This enables comparing the
fine structures between the surface and core regions of the nanoparticles. The
results confirm earlier observations of uniformly oriented spin canting
structure for CFO with additional information on atom site-selective spin
canting information. In case of Fe3O4 preferred canting orientation forming
core and shell structure is deduced. Unlike earlier reports based on polarized
spin-flip neutron scattering measurement, it is possible to narrow down the
possible canting angles for Fe3O4 (Td, Oh tilts 40{\deg}, 40{\deg}) and CFO
(Td, Oh tilts 17{\deg}, 17{\deg}) from the experimental spectra combined with
the first principle based calculation considering non-collinear magnetism. In
addition, the role of Dzyaloshinskii-Moriya interaction in stabilizing the spin
canting at the nanoparticle surface is discussed. The results demonstrate that
HREELS can be a powerful technique to probe the magnetic structure in
nano-dimensional systems and has advantages over neutron based techniques in
terms of superior spatial resolution, site specific information and easy of
sample preparation.
