In most materials, magnetic phenomena at room temperature and below are essentially independent of the masses of the nuclei of the constituent atoms. The atoms can usually be considered as infinitely heavy and static in theoretical descriptions of such phenomena, although there are exceptions. Over a decade ago, Kim showed how atomic motion could result in small but measurable changes in the properties of 'itinerant' ferromagnets. It is therefore not so surprising that atomic motion might have a measurable effect on the temperature below which lanthanum-based man-ganites become ferromagnetic (the Curie temperature, T_c). But the magnitude of the effect, as reported by Zhao et al. on page 676 of this issue, is alarming.
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