Work function changes in the double layered manganite La1.2Sr1.8Mn2O7 - art. no. 134428

We have investigated the behavior of the work function of La1.2Sr1.8Mn2O7 a s 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 (12 5 K) of the sample. Above T-C the work function appears to be roughly const ant. Our results are exactly opposite to the work function changes calculat ed from the double-exchange model [N. Furukawa, J. Phys. Soc. Jpn. 66, 2528 (1997)] but are consistent with other data. The disagreement with double e xchange can be explained using a general thermodynamic relation valid for s econd order transitions [D. van der Marel and G. Rietveld, Phys. Rev. Lett. 69, 2575 (1992); D. van der Marel, D. I. Khomskii, and G. M. Eliashberg, P hys. Rev. B 50, 16 594 (1994)] and including the extra processes involved i n the manganites besides double-exchange interaction.