Specific heat of Pr-0.6(Ca1-xSrx)(0.4)MnO3 (0 <= x <= 1)

We present the results of a specific heat study of the Pr-0.6(Ca1-xSrx)(0.4 )MnO3 (0 less than or equal to x less than or equal to 1) manganite system as a function of doping concentration x and temperature. The low-temperatur e specific heat data indicate that these materials have Debye temperatures of 333-344 K and reveal the presence of a 1/T-2 hyperfine term. For x great er than or equal to 0.25 the samples are metallic ferromagnets at low tempe rature with gamma values of 4.5-5.7 mJ/mol K-2 However, no T-3/2 term assoc iated with the presence of ferromagnetic spin waves can be resolved in the data. As x decreases below x = 0.25, the materials become increasingly insu lating in character and antiferromagnetic order is preferred. The x = 0.0 s ample is an antiferromagnetic charge ordered insulator. In this doping regi me, the low-temperature specific heat contains an additional contribution w hich is attributed to the presence of antiferromagnetic spin waves. The hig h-temperature specific heat data clearly show the onset of the charge and m agnetic ordering. The entropy loss accompanying the magnetic transition in each of these materials is much smaller than expected. This discrepancy is attributed to a combination of factors, including the localization of charg e carriers around the metal-insulator transition which occurs at the Curie temperature T-c in the x greater than or equal to 0.25 ferromagnetic materi als and the presence of short range magnetic correlations, well above the m agnetic ordering temperature. [S0163-1829(99)16001-6].