MAGNETIC-PROPERTIES OF THE IRON ARSENATE PHASE FE2AS4O12 - SHORT-RANGE VERSUS LONG-RANGE ORDER

A novel route for the preparation of Fe(2)AS(4)O(12) is reported. This oxide crystallizes in the space group P6(3) with the unit cell dimensions a = 14.743(7) Angstrom and c = 7.638(1) Angstrom, with Z = 6. The main structural feature of this material is the presence of Fe2O912- dimers which are connected with each other in a 3-D network via AsO(4)(3-)tetrahedra. Susceptibility data were measured down to 5 K. The susceptibility attains a maximum at about 50 K. Although the crystal structure favors dimer-like shea-range ordering, long-range order dominates in this material and the dimer-like correlations are extremely weak or even absent. The data between 80 and 300 K were fitted to the Curie-Weiss law with an effective moment of 5.75(7) mu(B) and Weiss constant equal to -95 K. The magnetically ordered state was studied by low-temperature neutron diffraction. The magnetic reflections were indexed on the chemical cell with the propagation vector k = (000), and the moments were found to lie normal to the c axis. The Neel temperature is 40 K.