  We have computationally studied the properties of higher-order magnetic
anisotropy constants in an L10/A1-FePt coreshell system which is characterized
by a strong second-order 2-ion Fe-Pt anisotropy component. We show that the
coreshell structure induces an unexpected fourth-order anisotropy constant K2
the magnitude of which varies non-monotonically with the core-size ratio R
reaching a peak at R = 0.50. Furthermore, we find that K2 scales with the
normalized magnetization by (M/Ms)^2.2 at temperatures below the Curie
temperature - a remarkable deviation from the established Callen-Callen theory
which instead predicts a scaling exponent of 10. We construct an analytic model
which demonstrates K2 arises from the canting of the core and shell
magnetization, and successfully reproduces and justifies the scaling exponent
obtained from numerical simulation.
