Epitaxial LaFeO3 and LaFe0.75Zn0.25O3 thin films on SrTiO3 (STO) (100) substrate: Structural studies and high energy magnon excitations

Abstract

The epitaxial films of LaFeO3 (LFO) and LaFe0.75Zn0.25O3 (LFZO) are grown on a SrTiO3 (STO) (100) substrate using pulsed laser deposition. The as-grown films have been investigated to study the structural properties and magnon excitations using temperature dependent Raman spectroscopy. X-ray diffraction and high resolution x-ray diffraction reciprocal space mapping indicate the epitaxial growth of films on the STO (100) substrate. RSM shows the broadening of the diffraction spot in the qz direction that may be due to the tilt present in the thin films, suggesting the orthorhombic growth of the films. Raman measurements on LFO and LFZO thin films have been performed for structure identification. The absence of first order phonon modes in Raman spectra suggests that the structure of films is symmetric and is coherent with the cubic substrate. High energy Raman bands with typical characteristics of two-magnon scattering appear below Neel temperature. Splitting of magnon branches is seen for both LFO and LFZO films and has been analyzed on the basis of the magnetic structure of LFO. The hardening of the magnon modes is observed as the temperature approaches towards the Neel temperature that may be attributed to the lattice contraction and correlated with a decrease in the tilt and a corresponding increase in the Heisenberg exchange constant (J) leading to a more ordered state at Neel temperature.