Electronic reconstruction and interface engineering of emergent spin fluctuations in compressively strained <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>La</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub>

Motivated by the recent observation of ambient-pressure superconductivity with $T_c \sim 40$ K in La3Ni2O7 on SrLaAlO4(001) (SLAO), we explore the structural and electronic properties as well as the spin-spin correlation function of this bilayer nickelate system by using density functional theory including a Coulomb repulsion term. We find that the compressive strain exerted by this substrate leads to an unconventional occupation of the antibonding Ni $3d_{z^2}$ states around the $Γ$ point, distinct from the superconducting bulk compound under pressure. While pure strain effects rather modestly enhance the dynamical spin susceptibility, investigation of a reconstructed interface composition as observed in transmission electron microscopy uncovers a strong amplification of the spin fluctuations due to Fermi surface nesting of the antibonding Ni $3d_{z^2}$ states near the interface. These results provide insights into the emergence of superconductivity in strained La$_3$Ni$_2$O$_7$, suggest a possible key role of the interface, and highlight fundamental differences from the hydrostatic pressure scenario.