The important role of local distortions and their connection with magnetism and transport in the “colossal” magnetoresistance systems, La_1-xA_xMnO₃

Abstract

Large magnetoresistance (MR) effects have been observed in the substituted systems La_1-x A _x MnO₃ (A = Sr, Ca, Ba, Pb, etc.). Most work have been interpreted in terms of the double-exchange (DE) model which assumes Mn⁺³ and Mn⁺⁴ sites exist. Recently Millis has suggested that local distortions, in the form of polarons, must also be present to explain the magnitude of the MR. We present X-ray absorption fine structure (XAFS) data which confirm that local distortions are indeed present and show that the distortions are correlated with magnetization. However, the near edge data are not consistent with charge localization on some of the Mn sites; all Mn appear to have the same average valence.

Key Words:

• CMR
• XAFS
• Polarons