Signatures of room-temperature magnetic glassiness in zinc ferrite epitaxial thin films

Abstract

Zinc ferrite (ZnFe 2 O 4 ) epitaxial thin films were grown by reactive magnetron sputtering on MgAl 2 O 4 and Al 2 O 3 substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ZnFe 2 O 4 with the nominal stoichiometric composition and long-range magnetic order at and above room temperature. The main preparation parameter influencing the temperature T f of the bifurcation between M(T ) curves under field-cooled and zero-field-cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:O 2 ratio did not systematically influence T f . Furthermore T f was found to be systematically higher for MgAl 2 O 4 as substrate and T f extends to above room temperature. While in some samples T f seems to be more likely correlated with superparamagnetism, the highest T f occurs in ZnFe 2 O 4 epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective x-ray magnetic circular dichroism measurements aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ZnFe 2 O 4 .