On the nature of the phase transition in MnO

The temperature dependence of the nuclear Bragg reflection (222) and of the magnetic Bragg reflection (111) of MnO was simultaneously measured by neutron diffraction on a powder sample. The intensity of the nuclear line exhibits a 40% drop at temperatures between 113 and 116 K. This dip was attributed to a decrease of the Bragg intensity due to structural fluctuations. If the effect of these fluctuations on the magnetic intensity is taken into account, the magnetization discontinuity is found to be greatly reduced or even to disappear, in disagreement with other authors.