Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films

摘要

Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial growth of spinel NiFe2O4ultrathin films onto SrTiO3 single crystals. We will show that—under appropriate growth conditions—epitaxialstabilization leads to the formation of a spinel phase with magnetic and electrical properties that radically differfrom those of the bulk material: an enhanced magnetic moment sMSd—about 250% larger—and a metalliccharacter. A systematic study of the thickness dependence of MS allows us to conclude that its enhanced valueis due to an anomalous distribution of the Fe and Ni cations among the A and B sites of the spinel structureresulting from the off-equilibrium growth conditions and to interface effects. The relevance of these findingsfor spinel- and, more generally, oxide-based heterostructures is discussed. We will argue that this novelmaterial could be an alternative ferromagetic-metallic electrode in magnetic tunnel junctions