Multiferroicity and magnetoelectric coupling in doped ZnO

In this paper, we report the synthesis of pure ZnO, Li, Ni, and Mg doped (5 wt%) ZnO samples via sol-gel method and studied their structural, optical, ferroelectric and ferromagnetic properties. X-ray diffraction (XRD) analysis indicates the successful formation of ZnO phase. FESEM results show that the grain size of synthesized samples varies from 60 to 85 nm for pure and doped samples. It is observed that the value of dielectric constant and dielectric loss is maximum for pure ZnO which decreases for doped samples. Polarization versus electric field (P-E) loops of pure ZnO shows loosy capacitor behavior which tends towards non-linear ferroelectric behavior through the doping of Ni, Li and Mg in ZnO. Furthermore, the room temperature magnetization versus magnetic field (M-H) loops indicates the existence of ferromagnetism in pure, Ni, and Mg doped samples. However, Li doped ZnO sample shows an unusual behavior indicating the presence of both ferromagnetic and diamagnetic phases in the sample. The coexistence of both ferroelectricity and ferromagnetism simultaneously in Ni and Mg doped ZnO makes it a possible candidate for multiferroic devices. The coupling between ferroelectricity and ferromagnetism is measured through magnetoelectric (ME) coupling measurements which shows that the average value of second order magnetoelectric coefficient (β) increases from 5.23 × 10−6 to 3.08 × 10−4 μV/cm-Oe2 for pure to Ni doped ZnO samples, respectively. The room temperature multiferroicity with magnetoelectric coupling in Ni and Mg doped ZnO is not reported earlier as per our knowledge.