Study on target-film structural correlation in thin cobalt ferrite films grown by Pulsed Laser Deposition technique

Abstract

We prepared three films of crystalline cobalt ferrite under identical deposition conditions (time, temperature, pressure) using three different targets consolidated from CoFe2O4 (CFO) crystalline nanoparticles (NPs). The NPs were previously prepared by a chemical route varying their synthesis conditions in order to promote different variations in the degree of structural distortions. The purpose of this work is to study how the degree of crystal distortion of the precursor material (target) influences the structural properties of the films when they are grown by pulsed laser deposition (PLD). 57Fe Mössbauer spectroscopy was used to study the local environment of iron atoms in the powders (targets for PLD). The Williamson–Hall plots were used to show the degree of the strain present in the films. X-ray absorption near edge structure spectra of the films, taken in grazing incidence geometry, were also carried out. The results explicitly demonstrate that the film with the largest strain was deposited using structurally more imperfect CFO powders whereas the film with the smallest strain was grown using the best powder from the structural point of view. These results were reinforced indirectly by magnetic measurements (exchange bias effect) in Fe/CFO bilayers (thin iron film was deposited additionally for this purpose) when hysteresis loops were analyzed after field cooling at a 3 T magnetic field. We show that the quality of thin cobalt ferrite films depends on the quality of the precursor material when the PLD technique is involved.