Specific-heat study for ferromagnetic and antiferromagnetic phases in SrRu_1-xMn_xO₃

Low-temperature electronic states in SrRu_1-xMn_xO ₃ for x ≤ 0.6 have been investigated by means of specific-heat C_p measurements. We have found that a jump anomaly observed in C _p at the ferromagnetic (FM) transition temperature for SrRuOs changes into a broad peak by only 5% substitution of Mn for Ru. With further doping Mn, the low-temperature electronic specific-heat coefficient γ is markedly reduced from the value at x = 0 (33 mJ/K²mol), in connection with the suppression of the FM phase as well as the enhancement of the resistivity. For x ≥ 0.4, γ approaches to ∼ 5 mJ/K² mol or less, where the antiferromagnetic order with an insulating feature in resistivity is generated. We suggest from these results that both disorder and reconstruction of the electronic states induced by doping Mn are coupled with the magnetic ground states and transport properties.