Strain modulated magnetocaloric effect in (111) oriented La0.7Sr0.3MnO3–SrRuO3 superlattices

Abstract

Magnetocaloric effect in (111)-oriented La_0.7Sr_0.3MnO₃–SrRuO₃ (LSMO–SRO) superlattices grown with both the stacking orders by reversing the individual layer thickness on (111)-oriented SrTiO₃(STO) substrates using the pulsed laser deposition technique has been studied. Pseudomorphic growth with 0.64% in-plane tensile strain in [11 unit cell (u.c.)SRO/3u.c.LSMO]_×15 superlattice is favourable for a larger change in entropy (ΔS_M) as compared to relaxed growth with in-plane compressive strain in [11u.c.LSMO/3u.c.SRO]_×15 superlattice. The reduction of ΔS_M in [11u.c.LSMO/3u.c.SRO]_×15 could be due to the orientation-dependent in-phase and out-of-phase tilt of the unit cell between ±1° along the 〈103〉_pc of the {103}_pc, which softens the exchange coupling and leads to the faster alignment of the magnetization near the Curie temperature (T_C). Stabilization of the orthorhombic phase of LSMO in the superlattices with both stacking orders is evidenced from the existence of anomaly around the T_C of LSMO and SRO in the temperature-dependent phonon frequency shifts. Reduction in symmetry of LSMO from the rhombohedral to orthorhombic structure modulates the Mn–O–Mn bond length and angles, which induces the spin reorientations and hence, modifies the electronic and magnetic properties in these LSMO–SRO superlattices. The ΔS_M of these superlattices suggest that the strain, magnitude of the magnetic field, volume and magnetization of the ferromagnet can control the magnetocaloric effect. These results will be useful for designing the magnetic entropy based devices to improve renewable energy systems.