Co‐doping modulated magnetocaloric effect and critical behavior of kagome MgMn₆Sn₆

Single crystals of MgMn 5.95 Co 0.05 Sn 6 were synthesized via the flux method, and their magnetic properties, magnetocaloric effects, and critical behavior were systematically investigated. Compared to the ferromagnetic (FM) MgMn 6 Sn 6 parent compound, Co doping induces an antiferromagnetic‐like low‐magnetization state. The maximum magnetic entropy change under Δ H = 50 kOe was determined as 2.87 J/kg·K ( H // ab ) and 2.57 J/kg·K ( H // c ). Scaling analysis of the magnetic entropy change curves revealed a field‐dependent magnetic phase transition: a first‐order transition dominates at low magnetic fields ( H < 40 kOe), while a crossover to second‐order behavior occurs at higher fields ( H > 40 kOe). Critical exponents β , γ , and δ were derived using modified Arrott plots, Kouvel‐Fisher analysis, and the Widom scaling relation ( δ = 1 + γ / β ), with consistency validated through the universal scaling equation m = f ± ( h ). The critical exponents for H // ab align closely with the 3D‐Ising universality class, whereas those for H // c exhibit hybrid characteristics‐proximity to the 3D‐Heisenberg model below T C and mean‐field behavior above T C . These findings highlight the anisotropic critical behavior and universality crossover induced by Co doping in the MgMn 6 Sn 6 system.