Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films

TL;DR

This study demonstrates that epitaxial growth of NiFe2O4 ultrathin films on SrTiO3 can produce a spinel phase with significantly enhanced magnetic moments and metallic behavior, differing from bulk properties.

Contribution

It reveals how off-equilibrium growth conditions induce a novel magnetic and conductive phase in NiFe2O4 ultrathin films, with potential applications in spintronics.

Findings

Magnetic moment increased by about 250% in ultrathin films

Films exhibit metallic conduction unlike bulk NiFe2O4

Enhanced properties linked to cation distribution and interface effects

Abstract

Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial growth of spinel NiFe2O4 ultrathin films onto SrTiO3 single-crystals. We will show that - under appropriate growth conditions - epitaxial stabilization leads to the formation of a spinel phase with magnetic and electrical properties that radically differ from those of the bulk material : an enhanced magnetic moment (Ms) - about 250% larger - and a metallic character. A systematic study of the thickness dependence of Ms allows to conclude that its enhanced value is due to an anomalous distribution of the Fe and Ni cations among the A and B sites of the spinel structure resulting from the off-equilibrium growth conditions and to interface effects. The relevance of these findings for spinel- and, more generally, oxide-based heterostructures is discussed. We will argue that this novel material could be an alternative ferromagetic-metallic electrode in magnetic tunnel junctions.