Abstract
Measurements of the field and temperature dependent electricalresistivity and ac susceptibility of LaMnO3 doped with 5% Mgare presented. Analysis of these data reveal that while this system undergoes a ferromagnetic transition at Tc = 147.2±0.2 K, it remains semiconducting over the entire temperaturerange examined (90⩽T⩽330 K). In particular, theseresistivity data are well fit by the form appropriate foradiabatic small polaron hopping for both T>Tc and T<Tc. These fits also indicate a distinct drop in thecharacteristic hopping energy Ea on entering theferromagnetic phase which presumably reflects a significantmagnetoelastic influence on the polaron dynamics. Such ascenario can be accounted for specifically in recent theoriesinvolving bipolaron formation in the paramagnetic phase, howeverthe persistence of polaronic hopping - rather than metallictransport/polaronic tunnelling - in the ordered phase would beindicative of triplet, rather than singlet, pairing at all temperatures within such a model.
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