Cador, O., Price, D.J., Larionova, J., Mathoniere, C., Kahn, O., and Yakhmi, J.V. (1997) Dc and ac magnetic properties of the two-dimensional molecular-based ferrimagnetic materials A2M2[Cu(opba)]3nsolv [A+ = cation, MII = MnII or CoII, opba = ortho-phenylenebis(oxamato), and solv = solvent molecule]. Journal of Materials Chemistry, 1997 (7). pp. 1263-1270. ISSN 0959-9428 (doi:10.1039/A700272F )
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This paper is devoted to a thorough study of the magnetic properties, both in the dc and ac modes, of two-dimensional ferrimagnetic materials. The general formula of the compounds, abbreviated as A2M2Cu3, is A2M2[Cu(opba)]3_nsolv where A+ stands for a counter cation (radical cation, alkali-metal or tetraalkylammonium), opba is ortho-phenylenebis(oxamato), MII is MnII or CoII , and solv is a solvent molecule (Me2SO or H2O). The dc magnetic susceptibility data for all compounds down to ca. 50 K are characteristic of two-dimensional ferrimagnets. In the A2Mn2Cu3 series, three classes of compounds have been distinguished. Class I has a unique representative, AV2Mn2Cu3, where AV+ is the radical cation 2-(1-methylpyridinium-4-yl )-4,4,5,5- tetramethylimadozolin-1-oxyl-3-oxide, the structure of which has already been solved. This compound is a magnet with Tc= 22.5 K. Class II corresponds to compounds with large cations (tetraethyl- and n-tetrabutylammonium). They also behave as magnets with Tc around 15 K. Class III corresponds to compounds with small cations (alkali-metal ions and tetramethylammonium). They behave as metamagnets with a long-range antiferromagnetic ordering in zero field around 15 K, and a field-induced ferromagnetic state. The critical fields are of the order of 0.15 kOe. All the A2Co2Cu3 compounds are magnets with Tc around 30 K. Furthermore, the cobalt derivatives show a very strong coercivity, with coercive fields of several kOe at 5 K. They also display a pronounced magnetic after-efect in the ordered phase. In the course of this work several peculiar features have been observed. In particular, the A2Mn2Cu3 compounds have been found to present weak but significant negative out-of-phase ac magnetic signals at temperatures just above Tc. All the observed phenomena are discussed and, in particular, a mechanism for the long-range ordering in these two-dimensional compounds has been proposed
|Glasgow Author(s):||Price, Dr Daniel|
|Authors:||Cador, O., Price, D.J., Larionova, J., Mathoniere, C., Kahn, O., and Yakhmi, J.V.|
|College/School:||College of Science and Engineering > School of Chemistry|
|Journal Name:||Journal of Materials Chemistry|
|Journal Abbr.:||J. Mater. Chem.|