We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as a function of temperature by means of photoemission. We found a decrease of 55 +/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of the sample. Above T_C the work function appears to be roughly constant. Our results are exactly opposite to the work function changes calculated from the double-exchange model by Furukawa, but are consistent with other measurements. The disagreement with double-exchange can be explained using a general thermodynamic relation valid for second order transitions and including the extra processes involved in the manganites besides double-exchange interaction.
Cite
@article{arxiv.cond-mat/0105531,
title = {Work function changes in the double layered manganite La1.2Sr1.8Mn2O7},
author = {K. Schulte and M. A. James and L. H. Tjeng and P. G. Steeneken and G. A. Sawatzky and R. Suryanarayanan and G. Dhalenne and A. Revcolevschi},
journal= {arXiv preprint arXiv:cond-mat/0105531},
year = {2009}
}