Analysis of Mechanical-magnetic Coupling Characteristics of NiFe₂O₄ Thin Film Based on Modified Bulge Tests

A modified multiple functional bulge apparatus andbulge mechanical-magnetic constitutive equation were introduced to study the mechanical-magnetic characteristics of NiFe₂O₄ (NFO) film materials. NFO thin film bulge samples were prepared by sol-gel and chemical etching methods. Magneto-mechanical characteristics of NFO thin film were studied under different mechanical and magnetic loads. The results show that residual stress and elastic modulus of NFO thin films were about 500.8 MPa and 187.8 GPa, respectively, under no external magnetic field state. As the magnetic field increased from 0 Oe to 800 Oe, the elastic modulus increased from 187.8 GPa to 484.6 GPa. The corresponding magnetostriction coefficient varies from -94.2×10^-6 to -326.2×10^-6 with the increase of applied magnetic fields from 200 Oe to 800 Oe.When the bulge oil pressure changes from 0 kPa to 50 kPa, the residual polarization of NFO film decreased by 75% and the coercive field decreased by 44%.