Influences of the first-to-second order magnetic phase transformation on the transport properties of La0.7Ca0.3-xBaxMnO3 compounds.

We studied the influence of the magnetic phase transition on the transport properties of La_0.7Ca_0.3-xBa_xMnO₃ compounds with x = 0.05, 0.075, and 0.10. Our experimental results demonstrated the ferromagnetic-paramagnetic and metal-insulator transitions taking place at temperatures T_C = 265-300K and T_MI = 280-310 K, respectively, which increase with increasing Ba-doping content. While the x = 0.05 sample undergoes a first-order magnetic phase transition (FOMT), x = 0.10 undergoes a second-order magnetic phase transition (SOMT). The other sample with x = 0.075 is considered as a threshold concentration of the FOMT-SOMT transformation. Further, q(T) data in different temperature regions were fitted to different models. The activation energy E_p and density of states at the Fermi level N(E_F) were accordingly determined. Notably, N(E_F) increases while E_p decreases in the case of applying an external field. We also have found that N(E_F) increases when materials transfer from the FOMT to the SOMT, which becomes smallest for the sample having the coexistence of the FOMT and SOMT (i.e., x = 0.075). [ABSTRACT FROM AUTHOR]