We report the investigations of resistivity and specific heat on the colossal magnetoresistance (CMR) compound La0.7Sr0.3(Mn1−xRux)O3 as a function of temperature with x = 0 to 0.25. It is found that the specific heat undergoes pronounced peaks due to the ferromagneticparamagnetic phase transition in these compounds. However, the transition temperatures TC determined from the specific heat are consistently lower than that of the metal-insulator transitions TMI determined from the resistivity measurements. By replacing Mn with Ru, both TC and TMI concurrently decrease and the studied materials are driven toward to the insulating phase with larger x. It is also found that the entropy change during the phase transition is reduced with more Ru substitution. These observations indicate that the existence of Ru has the effect of weakening the ferromagnetism and metallicity to the La0.7Sr0.3MnO3 perovskite. PACS numbers: 75.30.K, 74.62.Dh, 75.40.C I
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