Dependence of the magnetism-resistivity correlation on Curie temperature in manganites

The ferromagnetic order in La_0.67Ca_0.33MnO ₃ (LCMO) films has been tuned both by vacuum annealing and substrate-induced strain. And the relation between magnetization (M) and resistivity (ρ) was investigated as a function of Curie temperature (T _C). With decreasing T_C, the magnetoresistance (MR) increases, reflecting the stronger magnetism-resistivity correlation at lower T_C. It is interestingly found that the relation between ρ and M maintains a form of ρ=^ρ0exp(-M/α) for temperature near and slightly below T_C despite the fact that T_C is tuned over a wide temperature range, which reveals the dominant role of magnetic polaron on the transport properties. More interestingly, by exploring the ρ-M dependence of LCMO combined with the results of La_0.67Sr _0.33Mn_1-xFe_xO₃, it is found that the coefficient α decreases universally with the reduction T_C. This implies the tunability of the magnetic polaron could be an important reason for the stronger magnetism-resistivity correlation at lower T_C. Further analysis show that the variation T_C is associated with Jahn-Teller energy and electronic band width, which also confirm the important role of the lattice polaron on the property of the manganite. These results not only provide a universal description of the dependence of the magnetism-resistivity correlation on T_C, but also demonstrate the importance of the accompanying occurrence of spin-lattice and charge-lattice couplings in the manganites.