Small magnetic polaron effect in lithium iron phosphates

Abstract

The small polarons in LiFePO4 are associated with the presence of Fe3+ ions introduced by the native defects in relative concentration \({{\left[ {{\text{Fe}}^{3 + } } \right]} \mathord{\left/ {\vphantom {{\left[ {{\text{Fe}}^{3 + } } \right]} {\left[ {{\text{Fe}}^{2 + } + {\text{Fe}}^{3 + } } \right]}}} \right. \kern-\nulldelimiterspace} {\left[ {{\text{Fe}}^{2 + } + {\text{Fe}}^{3 + } } \right]}} = 3 \times 10^{ - 3} \) in the samples known to be optimized with respect to their electrochemical properties. The nearest iron neighbours around the central polaron site are spin-polarized by the indirect exchange mediated by the electronic charge in excess. These small magnetic polarons are responsible for the interplay between electronic and magnetic properties that are quantitatively and self-consistently analysed. Comparison is made with other magnetic polaron effects in other members of the family of magnetic semiconductors to which this material belongs.