Transition from the paramagnetic to the antiferromagnetic state actualized in FeBr2

The magnetic ordering process of the antiferromagnet FeBr2 has been studied by measuring low-field dc-magnetization, ac-susceptibility and the Mossbauer spectrum. All quantities measured show anomalous behaviour around the Neel temperature TN = 14.2 K. We propose defining Tp (>TN) by the temperature where the magnetization is maximum. Because it is Tp, not TN, that signifies the onset of magnetic ordering. We indicate that FeBr2 transforms from the paramagnetic to antiferromagnetic (AF) state through an intermediate AF domain state which exists in a certain narrow temperature region ΔT just below Tp. From the fact that ΔT is sample-dependent, we have inferred that the stacking fault of the hexagonal c-layers plays an important role in the formation of the intermediate AF domain state.