Effects of carbon deficiency on the magnetic interactions in GaCMn sub(3), a critical behavior study

We report a comparison study of the critical behavior near the ferromagnetic (FM) transition (T sub(C)) for stoichiometric GaCMn sub(3) and carbon deficient GaC sub(0.8)Mn sub(3). For GaCMn sub(3), the obtained critical exponent beta that describes the ferromagnetic (FM) coupling below T sub(C) is slightly reduced compared with the Mean Field (MF) value. In GaC sub(0.8)Mn sub(3), the value of beta is further decreased towards the anticipated value of the 3D Heisenberg model. However, another critical exponent gamma relevant to the paramagnetic behavior is slightly larger than the MF magnitude and insensitive to the carbon deficiency. The change in critical behavior accords with the modification of the electronic structure, i.e., the carbon deficiency weakens the Mn 3d-C 2p hybridization and thus increases the localization of Mn 3d states. Consistently, the specific heat study shows an enhancement of density of state at the Fermi level in GaC sub(0.8)Mn sub(3) compared with GaCMn sub(3), which further confirms the weakening of Mn 3d-C 2p hybridization due to carbon vacancies.