Atomic structure, magnetism, and transport properties of damaged La0.67Ca0.33MnO3-δ processed via high-energy ball milling

A La0.67Ca0.33MnO3-delta alloy was produced via a low-temperature solid state reaction in a high-energy ball mill. The milled alloy is found to exhibit the paramagnetic-to-ferromagnetic (P-F) transition at 150 K. However, the widely reported insulator-to-metal (I-M) transition that usually accompanies the P-F transition is totally suppressed. Anneals at 500-1000 degrees C in air (t = 8 h) are found to lower the resistivity but not restore the I-M transition. The suppression of the I-M transition is attributed to anion defects in the structure that have not been annihilated during heat treatments. Extended x-ray absorption fine structure is employed to track the evolution of the atomic structure around the Mn cations at various stages of processing. (C) 1999 American Institute of Physics. [S0021-8979(99)09115-X].