Polaronic transport in both the paramagnetic and ferromagnetic phases of La0.95Mg0.05MnO3

Measurements of the field and temperature dependent electrical resistivity and ac susceptibility of LaMnO3 doped with 5% Mg are presented. Analysis of these data reveal that while this system undergoes a ferromagnetic transit ion at T-c = 147.2 +/- 0.2 K, it remains semiconducting over the entire tem perature range examined (90 less than or equal to T less than or equal to 3 30 K). In particular, these resistivity data are well fit by the form appro priate for adiabatic small polaron hopping for both T, T,and T < T-c, These fits also indicate a distinct drop in the characteristic hopping energy E- a on entering the ferromagnetic phase which presumably reflects a significa nt magnetoelastic influence on the polaron dynamics. Such a scenario can be accounted for specifically in recent theories involving bipolaron formatio n in the paramagnetic phase, however the persistence of polaronic hopping-r ather than metallic transport/polaronic tunnelling-in the ordered phase wou ld be indicative of triplet, rather than singlet, pairing at all temperatur es within such a model.