We present a magnetotransport investigation of single crystal Pr 0.65(Ca0.75Sr0.25)0.35MnO 3, a manganite system specifically tailored to result in a close competition between ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Below 165 K these phases coexist spatially, with application of a magnetic field favoring the ferromagnetic metallic phase, leading to a magnetoresistance ratio of>1010 in a 2 T magnetic field. Isothermal resistivity vs. field measurements reveal some previously unobserved features accompanying the insulator to metal transition. In addition to unexpected fine structure that occurs as the ferromagnetic metallic phase grows to engulf the entire sample, we observe an intriguing "overshoot" phenomenon in both temperature and field-driven insulator-metal transitions. The resistivity is found to reach a sharp minimum (lower even than the pure ferromagnetic metallic phase) close to the point where the metallic phase percolates. These features are explored in detail and we discuss possible explanations of the effects in terms of pinning of the spatial boundary between the magnetic phases, and the unusual transport effects that could occur when the current flows through a barely percolated path.
Bibliographical noteFunding Information:
Work at Argonne National Lab was partially supported by the US Department of Energy, Office of Science under contract no. W-31-109-ENG-38. Acknowledgement is made to the donors of the American Chemical Society Petroleum Research Fund for partial support of the research at UMN. C.L. would like to acknowledge illuminating discussions with P.A. Crowell and P. Schiffer. J.W. and C.L. thank R. Compton for assistance with magnetization and transport measurements.
- Colossal magnetoresistance
- Metal-insulator transition
- Phase separation