Impact of anti-phase boundary on the magnetocaloric effect in geometrically frustrated epitaxial MnCr2O4

In epitaxially grown spinel thin films, the anti-phase boundaries (APBs) are formed due to cationic rearrangements within the spinels on the lattice-mismatched substrates. We demonstrate that such an APB formation could significantly influence the magnetocaloric effect (MCE) and suggest a model on how to avoid their formation and detrimental effects on MCE. We fabricate the geometrically frustrated epitaxial MnCr2O4 on SrTiO3 substrate with two different concentrations of APBs. The film with largely dense APB shows an entropy change, −ΔSM of ∼ 1.3 J/Kg-K, whereas the film with reduced APB shows a value of −ΔSM∼ 5.2 J/Kg-K for a change of field of 50 kOe. Furthermore, density functional theoretical calculations show that if there are more Jahn–Teller active A-site ions compared to B-site in an AB2O4 spinel, then such an APB formation is more probable. Hence, by creating a comparable fraction of Jahn–Teller active B-site cations, such an APB formation can be reduced. Moreover, avoiding the formation of APB and, thus, unwanted antiferromagnetic coupling at the boundaries could intrigue the future scientific community to design highly efficient magnetocaloric cooling devices using geometrically frustrated spinel systems.