Effects of carbon deficiency on the magnetic interactions in GaCMn3, a critical behavior study

• Above TC both GaCMn3 and GaC0.8Mn3 exhibit a mean-field-like critical behavior.
• Below TC GaC0.8Mn3 exhibits a 3D-Heisenberg-like critical behavior other than the mean-field behavior as GaCMn3 does.
• The 3D-Heisenberg-like critical behavior in GaC0.8Mn3 suggests a reduced Mn 3d-C 2p hybridization due to carbon deficiency.
• The specific heat measurement further confirms the weakening of Mn 3d-C 2p hybridization in GaC0.8Mn3 compared with GaCMn3.

We report a comparison study of the critical behavior near the ferromagnetic (FM) transition (TC) for stoichiometric GaCMn3 and carbon deficient GaC0.8Mn3. For GaCMn3, the obtained critical exponent β that describes the ferromagnetic (FM) coupling below TC is slightly reduced compared with the Mean Field (MF) value. In GaC0.8Mn3, the value of β is further decreased towards the anticipated value of the 3D Heisenberg model. However, another critical exponent γ 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 GaC0.8Mn3 compared with GaCMn3, which further confirms the weakening of Mn 3d-C 2p hybridization due to carbon vacancies.