Structural and magnetic properties of La2NiMnO6 thin films on LaAlO3 substrate with varying thickness

In the present work, the effect of film thickness on the structural and magnetic properties of La2NiMnO6 (LNMO) ferromagnetic double perovskite thin films has been systematically investigated. LNMO thin films of varying thickness from 54 nm to 256 nm were deposited using the pulsed laser deposition technique onto single-crystalline LaAlO3 substrate. The X-ray diffraction pattern and Raman scattering observations reveal that all films have c-axis epitaxial growth and an orthorhombic structure. The Raman spectra of the films are dominated by two broad peaks at around 534 cm−1 and 676 cm−1 assigned to the antisymmetric stretching (AS) and symmetric stretching (S) vibrations of the octahedra, respectively. The Raman peaks of the LNMO thin films are blue shifted in comparison to those of bulk LNMO and the shift increases with decreasing film thickness, indicating the increased influence of strain. The critical thickness for strain relaxation, as determined from the Raman spectra, is between 110 nm and 156 nm. However, the strain is observed to have large effect on the magnetic properties of films. Ferromagnetic to paramagnetic transition temperature (Tc) and the saturation magnetization were found to increase with increase in the film thickness. The film with thickness of 256 nm exhibits a saturation magnetic moment of 4.5 μB/f.u. and coercive field of 630 Oe at 10 K, with a Curie temperature close to 280 K.

► (0 0 2) peak shift toward the higher 2θ value as film thickness increases. ► Raman spectra shows two peaks located at around 534 cm−1 and 676 cm−1. ► Tc increases from 270 K (54 nm) to 278 K (256 nm) as the film thickness increases. ► All the films display hysteresis curves close to a rectangular shape.