Substrate-Induced Magnetic Anisotropy in Ni Thin Films.

Magnetic anisotropy in ferromagnetic thin films can be strongly influenced by interfacial strain arising from lattice mismatch and differences in the coefficient of thermal expansion (CTE) between the film and substrate. Understanding how film thickness and post-deposition annealing modify substrate-induced strain is essential for optimizing applications such as magnetic sensors, memory devices, and spintronic systems. Continuous Ni films of various thicknesses were deposited on 128° Y-cut LiNbO₃ and Z-cut LiTaO₃ substrates at room temperature using magnetron sputtering, and the strain–anisotropy coupling was examined via X-ray diffraction, temperature, and field-dependent magnetization. In the as-grown state, ultrathin Ni films (~ 5nm) exhibited pronounced anisotropy at low temperatures, attributed to the dominant influence of lattice-mismatch-induced strain. For thicker films (~100 nm), more isotropic behavior emerges, consistent with strain relaxation. However, post-deposition annealing reintroduces anisotropy in the films through mismatched CTE. These results provide fundamental insight and a practical route to tune substrate-induced strain and thereby control the evolution of magnetic anisotropy in Ni films, revealing reverse magnetoelastic coupling at the film-substrate interface.