Anomalous magnetic behavior of FeBr2 near the Neel temperature

Properties of the magnetic phase transition of the antiferromagnet FeBr2 have been studied by measuring low-field dc-magnetizations, ac-susceptibilities and Mossbauer spectra. All quantities measured show anomalous behaviors around and immediately below the Neel temperature T-N. Combining all the results, it is suggested that FeBr2 transforms from the paramagnetic to antiferromagnetic state through the intermediate domain state which exists in a certain narrow temperature region Delta T just below T-N. From the fact that the spread of Delta T 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 domain state. A new type of transition process from the paramagnetic to the ordered state is discussed.