Investigating the impact of lattice induced strain on the magnetic properties of NiFe2O4 in ultra-thin films

The magnetic ferrites are of significant interest in the field of spintronics; being magnetic insulators and having a highly tuneable inverse spinel structure. NiFe2O4 has a multitude of applications across electronic devices such as in high frequency microwave devices, magnetic memory drives and spin filters. The high functionality of NiFe2O4 across microelectronics has resulted in a substantial increase in the number investigations into understanding its magnetic properties. Induced lattice strain on NiFe2O4 via a substrate lattice mismatch has a profound effect on the observed magnetic properties. This research aims to compare the effects of tensile and compressive strains on NiFe2O4 and understand the in-plane and out of plane relationship on the changing magnetic properties. NiFe2O4 films were consistently grown via PLD on three different substrates: Al2O3, MgO and MgAl2O4, each inducing a lattice strain of 12.13%, 0.76% and -3.36% respec- tively, with an average thickness of 11 nm. Characterisations of the magnetic properties were taken by VSM - producing hysteresis loops - and structural properties undertaken by XRD and TEM. The results highlight the significance of the strain effect, particularly in relation to the angular dependence of coercive and retentive properties. The NiFe2O4 films were found to have in-plane emu/cc values of ∼200 on all three substrates. XRD data shows that NiFe2O4 was predominantly grown in the (222) plane and exhibited line broadening and peak shifts in accordance with the strain. TEM images show good single crystal growth and epitaxy on all three samples.