Critical behavior in Ag-doped managnites La0.67Pb0.33axAgxMnO3 (x=0.1 and 0.15)

The critical behavior of the La0.67Pb0.33axAgxMnO3 (x=0.1 and 0.15) was investigated by measurement of the magnetization around the Curie temperature TC. Experimental results revealed that these samples exhibit a second-order magnetic phase transition. The magnetic data were analyzed in the critical region using the KouvelaFisher method to yield the critical exponents of 0.352aOI2aO0.357 (from the temperature dependence of the spontaneous magnetization below TC), 1.272aOI3aO1.346 (from the temperature dependence of the inverse initial susceptibility above TC) and 4.563aOI'aO4.82 (from the critical magnetization isotherm M(TC, H)) with a TC of 288.37a316.39 K. The critical exponents values for La0.67Pb0.23Ag0.1MnO3 are very close to those found out by the 3D-Heisenberg model (I2=0.36, I3=1.39 and I'=4.8). Moreover, the estimated critical exponents of La0.67Pb0.18Ag0.15MnO3 are consistent with the prediction of the 3D-Ising model (I2=0.325, I3=1.241 and I'=4.82).