Improved ferromagnetism and transport behaviour in La2CoMnO6 double perovskite by Ni doping at the Co site

Doping at the transition metal oxide site of double perovskites offers distinct and fascinating functionality when compared to their undoped counterparts. In this work, magnetic and transport properties are investigated in detail in doped polycrystalline La2Co1-xNixMnO6 (x = 0 as La2CoMnO6, x = 0.1 as La2Co0.9Ni0.1MnO6, x = 0.5 as La2Co0.5Ni0.5MnO6) double perovskite systems. With Ni substitution at the Co site in the x = 0 sample, magnetic behaviour, particularly ferromagnetic transition temperature, increases, whereas coercive field and remanent magnetization decrease evidently for the x = 0.5 sample, implying the soft ferromagnetic nature. Magnetic investigations show an increase in the ferromagnetic transition temperature from ~ 230 K for the x = 0 to ~ 242 K for the x = 0.5 sample. The x = 0.5 sample exhibits a frustrated magnetic system due to competing magnetic couplings (Ni–Mn and Co–Mn ion pairs). Electrical resistivity measurements validate the semiconducting behaviour of all the studied systems near room temperature and insulating nature at low temperature regime along with resistivity anomaly near the magnetic ordering temperature. The system x = 0.1 shows large magnetoresistance value ~ −34% at ~ 150 K. The variable-range hopping model is used to best understand their transport mechanism.