Abstract :
The ferromagnetic order in La0.67Ca0.33MnO3 (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 (TC). With decreasing TC, the magnetoresistance (MR) increases, reflecting the stronger magnetism–resistivity correlation at lower TC. It is interestingly found that the relation between ρ and M maintains a form of ρ = ρ 0 exp ( − M / α ) for temperature near and slightly below TC despite the fact that TC 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 La0.67Sr0.33Mn1−xFexO3, it is found that the coefficient α decreases universally with the reduction TC. This implies the tunability of the magnetic polaron could be an important reason for the stronger magnetism–resistivity correlation at lower TC. Further analysis show that the variation TC 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 TC, but also demonstrate the importance of the accompanying occurrence of spin–lattice and charge–lattice couplings in the manganites.
