THE MAGNETIC-STRUCTURE OF NA5FEO4

The magnetic structure of the oxycompound Na//5FeO//4, showing discrete FeO//4**5** minus anions, has been determined by neutron diffraction. Spectra have been recorded at 2. 5, 15. 8, and 100 K, the Neel temperature having been found earlier equal to 5. 40 K by Moessbauer spectroscopy. A group theory analysis has been made, the magnetic group is Pb prime ca, the moments (M equals 3. 75 plus or minus 0. 1 mu //B at 2. 5 K) are parallel to the xoy plane, the angle with oy being equal to about 17 degree . The Fe**3** plus ions are coupled ferromagnetically parallel to oy and antiferromagnetically essentially in the xoz plane. The magnetic interactions have been analyzed and, the exchange integrals are small minus 2 K less than equivalent to J//i/k less than equivalent to 0. 5 K (i equals x,y,z).