Cobalt ferrite (CoFe2O4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment. It has also found use in contrast agents for magnetic resonance imaging. Use of ferrites in practical applications hinges on our ability to control size, solution behavior, and overall magnetic behavior. Having ferrites that are bio-compatible is an added bonus.

In this work we discovered that cobalt ferrite made by us showed an "inverse relationship" between the lattice constant and crystallite size. Usually as crystallite size decreases, lattice constant is found to increase. However in the cobalt ferrite made by us, we observe a decrease in lattice constant with decrease in crystallite size! In earlier reports where such an inverse trend was reported, researchers had employed vacuum based techniques to make cobalt ferrite. We observe this relatively exotic trend in cobalt ferrite made using low-temperature solution chemistry. We have developed a hypothesis for explaining the observation (it involves some stoichiometric arguments). However our hypothesis is yet to be tested. Further more, our results highlight ways in which size, and magnetic behavior can be optimized.