Room temperature multiferroic properties and magnetocapacitance effect of modified ferroelectric Bi4Ti3O12 ceramic

(Bi_3.15Nd_0.85)(Ti₂Fe_0.5Co_0.5)O_12-δ ceramics were prepared by the conventional solid-state reaction method. The sample of the layered perovskite phase was successfully obtained. The measurement of x-ray photoelectron spectroscopy indicated the coexistence of Fe³⁺ and Fe²⁺ ions. The multiferroic behaviour of the sample at room temperature (RT) was demonstrated by the ferroelectric (2P_r = 8 µC cm^-2, 2E_c = 64 kV cm^-1 at applied electric field 86 kV cm^-1) and ferromagnetic (2M_r = 32 m emu g^-1, 2H_c = 872 Oe at applied magnetic field 1.1 T) hysteresis loops. Remarkably, a clearly identified positive magnetocapacitance effect was observed with a large magnetocapacitance value of ∼14.2% at 30 kHz. Comparison of the impedance Cole-Cole plots measured with and without magnetic field revealed that the occurrence of magnetocapacitance effect is accompanied by an increase in the conductivity under magnetic field, which is explained by the enhancement of electron jumping in Fe²⁺-O-Fe³⁺ chains by magnetic field. The present results suggest a new candidate for a RT multiferroic material with large magnetocapacitance effect.