Non-collinear ferromagnetic short range order in MgO decked multi-layered graphene

A careful magnetic study of MgO decked multi-layered graphene (MDMLG), synthesized by a combustion process that does not involve the use of graphite (which can be a source of magnetic impurities) was conducted and an elaborate analysis of high-precision magnetization data permits us to completely rule out the presence of a long-range ferromagnetic (FM) ordering at temperatures T ≥ 2.5 K. Instead, a non-collinear FM short-range order persists up to temperatures as high as 300 K and a concomitant paramagnetic component is present at all the temperatures. The observed exponential temperature variations of the 'field-cooled' and 'zero-field-cooled' magnetizations, remanent magnetization, saturation magnetization, coercive field, exchange field and random anisotropy field are shown to basically reflect the exponential growth of the correlation length for the spins at the zigzag edges of graphene as the temperature falls below the temperature, T_x ≅ 10 K where a crossover from extremely weak to moderately weak magnetic anisotropy occurs. In sharp contrast, a paramagnetic response is induced by the defects in nanometer-sized MgO crystallites in MDMLG.