Sample-size resonance, ferromagnetic resonance and magneto-permittivity resonance in multiferroic nano-BiFeO3/paraffin composites at room temperature

• Nano-BiFeO3/paraffin composite shows a ferromagnetic resonance.
• Nano-BiFeO3/paraffin composite shows a magneto-permittivity resonance.
• Resonance of negative imaginary permeability in BiFeO3 is a sample-size resonance.
• Nano-BiFeO3/paraffin composite with large thickness shows a sample-size resonance.

In the present work, we demonstrate that ferromagnetic resonance and magneto-permittivity resonance can be observed in appropriate microwave frequencies at room temperature for multiferroic nano-BiFeO3/paraffin composite sample with an appropriate sample-thickness (such as 2 mm). Ferromagnetic resonance originates from the room-temperature weak ferromagnetism of nano-BiFeO3. The observed magneto-permittivity resonance in multiferroic nano-BiFeO3 is connected with the dynamic magnetoelectric coupling through Dzyaloshinskii–Moriya (DM) magnetoelectric interaction or the combination of magnetostriction and piezoelectric effects. In addition, we experimentally observed the resonance of negative imaginary permeability for nano BiFeO3/paraffin toroidal samples with longer sample thicknesses D=3.7 and 4.9 mm. Such resonance of negative imaginary permeability belongs to sample-size resonance.