  Mn2+ ion doping is used as an electron paramagnetic resonance (EPR) probe to
investigate the influence of low-coordination structural defects such as step
edges at the surface of terraced (001) MgO nanoparticles on the electronic
properties. Beside the well-known hyperfine sextet of Mn2+ ions in the cubic
crystal field of MgO, an additional EPR feature with a striking non-monotonous
temperature dependent shift of the g-factor is observed in terraced
nanoparticles in the temperature range from 4K to room temperature. By linking
the difference in the temperature dependence of the Mn2+ sextet intensity in
cubic and terraced nanoparticles with the possible s-d exchange shift and
enhanced Zeeman splitting we conclude that the novel EPR feature originates
from the loosely trapped charge-compensating carriers at the abundant
structural defects at the surface of terraced nanoparticles due to their
exchange interaction with neighboring Mn2+ ions.
