Possible weak ferromagnetism in pure and M (Mn, Cu, Co, Fe and Tb) doped NiGa₂O₄ nanoparticles

Abstract

We report on the structural and magnetic properties of nanoparticles of NiGa₂O₄ and 5 at.% M doped (M = Mn²⁺, Cu²⁺, Co²⁺, Fe³⁺ and Tb³⁺) at Ga site of NiGa₂O₄, synthesized by gel-combustion method. The particle size, as investigated by X-ray diffraction and transmission electron microscopy, could be fine tuned by a controlled annealing process. Weak ferromagnetism becomes significant, when the particles are in the nano regime (5–7 nm). The magnetization becomes insignificant at larger particle size (∼ 150 nm). Cu²⁺ and Tb³⁺ doped NiGa₂O₄ nanoparticles showed relatively large room temperature ferromagnetism compared to other doped (Fe, Mn and Co) and undoped NiGa₂O₄ samples. The weak ferromagnetism observed in the nanoparticles of NiGa₂O₄, which is antiferromagnetic in the bulk, is due to the surface disordered states with uncompensated spins.