Over the past three decades, there have been significant advances in energy efficiency technologies and quantum information processing within the field of spintronics [1], motivating the search for functional materials capable of generating and controlling spin currents with low energy consumption. In this context, mixed-valence manganites such as La_1−xSr_xMnO₃ (LSMO) have emerged as highly attractive candidates due to their strong coupling between lattice, charge, orbital, and spin degrees of freedom. This interplay gives rise to a rich phase diagram, including colossal magnetoresistance, half metallicity, and temperature-driven metal-insulator and magnetic phase transitions near room temperature, which are particularly appealing for sustainable spin-based devices such as magnetocaloric effect based devices [2], magnetic field and temperature sensors, magnetoelectric and memristive memories.

Among the mechanisms enabling spin-current generation, the longitudinal spin Seebeck effect (LSSE), driven by a vertical thermal gradient, represents a key phenomenon for spin-caloritronic applications, allowing the direct conversion of waste heat into spin and electrical signals[3]. In this work, we investigate the LSSE response in epitaxial La₁−ₓSrₓMnO₃ thin films with x ≈ 0.2. We focus in this x value due to its proximity to the ferromagnetic insulating–metallic phase boundary, where enhanced magnetic, electronic, and thermomagnetic responses are expected.

Epitaxial thin films were grown by pulsed laser deposition (PLD) on SrTiO₃ (STO) substrates. The thin film heterostructures with a Pt layer on the top and microwires contacts, were cooled below the Curie temperature and the LSSE voltage was measured by swiping the in-plane external magnetic field. The observed nontrivial temperature dependence of the thermoelectric signal strongly suggests a dominant magnon-mediated thermal transport mechanism. These results highlight the potential of LSMO-based heterostructures as efficient platforms for energy harvesting and thermomagnetic conversion, contributing to the development of sustainable spin-caloritronic devices.

To gain microscopic insight into the experimental observations, we also performed complementary first-principles density functional theory (DFT) calculations to investigate the evolution of the structural, electronic and magnetic properties for different Sr concentrations, both below and above x = 0.2.