Supercritical Carbon Dioxide‐Assisted Interface Formation of LaAlO ₃ /SrTiO ₃ for Room‐Temperature Ferromagnetism

ABSTRACT The LaAlO 3 /SrTiO 3 (LAO/STO) interface is a vital platform for emergent quantum phenomena, yet conventional methods for controlling its properties are often invasive. This work introduces supercritical CO 2 (SC CO 2 ) as a clean, tunable “physical strain field” to achieve a reversible diamagnetic‐to‐ferromagnetic transition in 3D LAO/STO composite powders via pressure tuning. Structural analysis reveals that under specific conditions (100°C, 14 MPa), SC CO 2 induces a tensile strain along the c‐axis in LAO. This strain is coupled through the coherent interface to the STO lattice, leading to cooperative lattice distortion without introducing significant chemical defects. Magnetic measurements confirm that the emergent ferromagnetism originates strictly from the interface and is precisely correlated with this unique lattice strain condition. This work unveils a new mechanism of interfacial lattice strain‐driven ferromagnetism and establishes a novel, non‐destructive paradigm for tuning quantum states at complex oxide interfaces using supercritical fluids.