Chemical Pressure Induced Strain Control of Magnetic Anisotropy in the Simple Perovskite ϵ-Fe₂O₃

ϵ-Fe₂O₃ is an exceptional nanoscale ferrimagnet, distinguished by its high coercivity (μ₀H_c > 2 T) and multiferroic behavior. Realizing its potential in advanced technologies requires precise control of its structural, electronic, and magnetic properties. Here, we report La-doping-induced chemical pressure arising from the larger ionic radius of La³⁺ substituting for Fe³⁺ that systematically modified the local chemical environments. These dopant-driven lattice strains and modified local chemical environments perturbed exchange pathways, producing a non-monotonic variation in saturation magnetization depending on the specific lattice sites occupied by La³⁺. Magnetic hysteresis concurrently revealed a remarkable rise in coercivity from ∼0.2 T for undoped nanoparticles (x = 0) to ∼2.3 T at x = 0.072, predominantly resulting from a strain-driven enhancement of magnetocrystalline anisotropy. These results established rare-earth substitution as an effective strategy to engineer strain-mediated changes in the nanomagnetism of ϵ-Fe₂O₃, offering a practical route to tailor high-coercivity and magnetoelectric properties for device applications.