  Incorporation of organic molecules into the lattice of inorganic crystalline
hosts is a common phenomenon in biomineralization, and has been shown to alter
various properties of the crystalline host. Taking this phenomenon as our
source of inspiration, we show herein that incorporation of specific single
amino acids into the lattice of manganese (II) carbonate strongly alters its
inherent magnetic properties. At room temperature, the magnetic susceptibility
of the amino-acid-incorporating paramagnetic MnCO3 decreases, following a
simple rule of mixtures. When cooled below the N\'eel temperature, however, the
opposite trend is observed, namely an increase in magnetic susceptibility
measured in a high magnetic field. Such an increase, accompanied by a drastic
change in the N'eel phase transformation temperature, results from a decrease
in MnCO3 orbital overlapping and the weakening of superexchange interactions.
