Time-Resolved Study of Polaron-Mediated Relaxation in Ferromagnetic La _0.67 Sr _0.33 MnO ₃ /BiFeO ₃ Thin Films by Dual-Color Pump–Probe Spectroscopy

High Resolution Image Download MS PowerPoint Slide La 0.67 Sr 0.33 MnO 3 /BiFeO 3 (LSMO/BFO) ferromagnet/antiferromagnet heterostructure thin films were grown on SrTiO 3 (100) substrates by pulsed-laser deposition, and their strain-dependent magnetic properties and ultrafast relaxation dynamics were investigated in comparison with single-layer LSMO films. For LSMO/BFO bilayers, increasing the BFO thickness from 40 to 120 nm reduces the coercive field from 8.34 to 3.52 mT and lowers the Curie temperature from 343 to 295 K, consistent with a BFO-thickness–controlled strain state in the LSMO layer that suppresses magnetization. In contrast, single-layer LSMO films exhibit increasing coercive field and Curie temperature with increasing LSMO thickness. Dual-color pump–probe spectroscopy further reveals a marked acceleration of carrier–lattice relaxation in LSMO/BFO: the electron–lattice coupling time decreases from 10.07 to 0.65 ps as BFO thickness increases, accompanied by GHz-range strain-pulse oscillations (18.99–24.48 GHz) and spin–lattice relaxation times approaching ∼100 ps. Single-layer LSMO shows much slower electron–lattice relaxation (>200 ps) and higher-frequency oscillations spanning ∼107.84–229.46 GHz, as determined from both FFT analysis and fitting of the oscillatory component, consistent with small-polaron-dominated transport. Together, these results demonstrate that BFO thickness provides an effective handle to tune strain, magnetic response, and ultrafast carrier–lattice dynamics in LSMO-based heterostructures, with implications for energy-conversion and spintronic applications through improved carrier transport efficiency and tunable magnetic functionalities.