Magnetoelectric coupling in multiferroic heterostructure of rf-sputtered NiMnGa thin film on PMNPT

In this paper, we report a preparation of multiferroic heterostructure from thin film of NiMnGa (NMG) alloy and lead magnesium niobatelead titanate (PMNPT) with effective magnetoelectric (ME) coupling between the film as ferromagnetic material and PMNPT as piezoelectric material. The heterostructure was prepared by relatively low temperature (400 °C) deposition of the film on single crystal of piezoelectric PMNPT substrate using rf magnetron co-sputtering of Ni ₅₀Mn ₅₀ and Ni ₅₀Ga ₅₀ targets. Magnetic measurements by Superconducting Quantum Interference Design (SQIUD) Magnetometer and Vibrating Sample Magnetometer (VSM) on the film revealed that the film is in ferromagnetically ordered martensitic state at room temperature with saturation magnetization of ∼240 emu/cm ³ and Curie temperature of ∼337 K. Piezoresponse force microscopy (PFM) measurement done at room temperature on the substrate showed the presence of expected hysteresis loop confirming the stability of the piezoelectric state of the substrate after deposition. Room temperature ME voltage coefficient (α _ME) of the heterostructure was measured as a function of applied bias dc magnetic field in LongitudinalTransverse (LT) ME coupling mode by lock-in technique. A maximum ME coefficient α _ME of 3.02 mV/cm Oe was measured for multiferroic NMG/PMNPT heterostructure which demonstrates that there is ME coupling between the film as ferromagnetic material and PMNPT as piezoelectric material.