Structural and magnetic properties of La2Ni1−xCoxMnO6 compounds

[Display omitted] •Monoclinic La2Ni1−xCoxMnO6 samples have been prepared using Sol-gel technique.•Rietveld analysis shows an octahedrally distorted double perovskite structure.•The nature of FM interaction and TC depend on the B-site ions.•The short range FM ordering above TC is induced by antisite disorders.•The existence of any spin glass like phase in such system is discarded. Single phase monoclinic La2Ni1−xCoxMnO6 (x = 0.2, 0.4, 0.8) compounds, henceforth, referred as LNCxMO (x = 0.2, 0.4, 0.8) have been prepared by Sol–gel technique. The structural study and redox titration suggest that the samples are both La and O deficient. The generated atomic models using Rietveld refined structural parameters show octahedral distortion in the double perovskite structure. X-ray photoelectron spectroscopy (XPS) study has been used to determine the predominant valence states of Ni, Mn and Co ions. LNCxMO (x = 0.2, 0.4) are found to be Heisenberg ferromagnets whereas LNC0.8MO is a phase segregated system. In LNC0.4MO and LNC0.8MO, at temperatures above TC, χ−1(T) curve shows the characteristics of Griffiths phase. The study of ac susceptibility and isothermal remanent magnetization (IRM) discard the possibility of any glassy state at low temperatures. The antiphase boundaries (APBs), antisite disorders (ASDs) and oxygen vacancies play important roles in this system.