  Single molecule magnets and single spin centers can be individually addressed
when coupled to contacts forming an electrical junction. In order to control
and engineer the magnetism of quantum devices, it is necessary to quantify how
the structural and chemical environment of the junction affects the spin
center. Metrics such as coordination number or symmetry provide a simple method
to quantify the local environment, but neglect the many-body interactions of an
impurity spin when coupled to contacts. Here, we utilize a highly corrugated
hexagonal boron nitride (h-BN) monolayer to mediate the coupling between a
cobalt spin in CoHx (x=1,2) complexes and the metal contact. While the hydrogen
atoms control the total effective spin, the corrugation is found to smoothly
tune the Kondo exchange interaction between the spin and the underlying metal.
Using scanning tunneling microscopy and spectroscopy together with numerical
simulations, we quantitatively demonstrate how the Kondo exchange interaction
mimics chemical tailoring and changes the magnetic anisotropy.
