Structure et propriétés magnétiques du composé NH4Fe3(H2PO4)6(HPO4)2,4H2O

✍ Scribed by A. Mgaidi; H. Boughzala; A. Driss; R. Clerac; C. Coulon

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 318 KB
• Volume: 144
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8137

✦ Synopsis

The title compound is prepared by adding aqueous ammonia to a solution of phosphoric acid containing a small amount of iron (III) ions (3%). It crystallizes in the monoclinic system, space group C2/c, a ‫؍‬ 16.8450(9) A > , b ‫؍‬ 9.6111(1) A > , c ‫؍‬ 17.6470(7) A > , and ‫؍‬ 90.91(2)°, R ‫؍‬ 0.031, and wR ‫؍‬ 0.078. The structure consists of a two-dimensional framework made of HPO 4 , H 2 PO 4 groups, and FeO 6 octahedra sharing corners. In one layer, the NH ؉ 4 cations are located inside 12 membered windows, which are generated by the corner-sharing FeO 6 and H 2 PO 4 . Water molecules lay in the interlayer space. With regard to magnetic properties, carried out in the range 1.7-300 K, the polycrystalline sample follows a Curie-Weiss law down to 30 K. At lower temperatures is a magnetic phase transition, where a spontaneous magnetization appears. This behavior suggests either a ferrimagnetic or a weak ferromagnetic order.