High Coercivity and Magnetization in WSe2 by Codoping Co and Nb

Introducing ferromagnetism in transition metal dichalcogenides has attracted lots of attention due to the possible applications in spintronics devices. Generally, single magnetic element doping is used to introduce magnetism. However, mostly, weak ferromagnetism is observed. In this work, codoping of two kinds of transition metals (Nb and Co) into WSe2 is used to study its magnetic properties. In detail, single crystal WSe2 is codoped with 4 at% Co and various concentrations of Nb by employing the physical ion implantation method. Raman, X-ray diffraction and X-ray photoelectron spectroscopy results reveal the effective substitutional doping of implanted elements (Co and Nb). Magnetic measurements illustrate that both un-doped and 4 at% Co doped WSe2 show weak ferromagnetism whereas magnetization is strongly enhanced when Co and Nb are codoped into WSe2. The magnetization is comparable with a ferromagnet, which may be attributed to Co, Nb doping and defects. In addition, a large coercivity of approximate to 1.2 kOe is observed in the 1 at% Nb-4 at% Co codoped WSe2 sample, which may be ascribed to the combined effect of doping-induced stress, defect-dictated pinning and anisotropy of Nb-Se bond owing to the charge transfer between Nb and Se ions.