Lattice defects formulated ferromagnetism in nonmagnetic La (III) ion doped NiO nanostructures: Role of oxygen vacancy

Abstract

During the last decade, room temperature ferromagnetism (RTFM) has been observed in doped transition metal oxides (TMOs) such as NiO. However, the origin of RTFM is not clearly understood and to date, it is highly debated. Here, we have investigated the origin of RTFM in nonmagnetic ion doped NiO, and consider the cubic structured La-doped NiO for this purpose. Single phase cubic structure of prepared samples revealed the absence of magnetic ion cluster and all the samples exhibit intrinsic cause of RTFM. Also, to address the only intrinsic reason of magnetism, we avoid the magnetic ion doping in NiO. By analysing the X ray diffraction (XRD), Raman analysis, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), the essential features of RTFM in doped NiO are found as: (i) almost hysteretic and temperature-independent magnetization (ii) non zero and high value of coercive field at high concentration of La (x = 0.05) that confirms the long-range ferromagnetism in doped NiO (iii) the saturation magnetization achieves a high value of 10.101 emu/g for La content (x = 0.01) confirming a sensation for saturation magnetization at this La content. These features demonstrate the RTFM in doped NiO are due to overlapped bound magnetic polarons (BMPs) created by the exchange interaction between the spin of La3+ ion and spin of the localized hole due to F center. Based on experimental and theoretical observations, it is suggested that the particular oxygen vacancy mediated exchange interaction between La3+-La3+ ions at higher concentration of La (x = 0.05) is responsible for the RTFM in doped NiO.