57Fe Mossbauer effect and magnetism down to 0.98K in the high-spin (5T2) to or from low-spin (1A1) system dithiocyanato bis(4-methyl-1, 10-phenanthroline) iron (II)

Abstract

The 57Fe Mossbauer effect and the magnetism of the ferrous compound Fe(4-CH3-phen)2(NCS)2 have been studied in detail between 4.2 and 309K and between 0.98 and 303.7K, respectively (phen=1,10-phenanthroline). Between 245 and 120K the compound shows a high-spin (5T2) to or from low-spin (1A1) transition centred at 215K. A study of magnetic hyperfine interactions at 4.2K shows that Vzz(1A1)<0. The reversal of the texture based line asymmetry in the Mossbauer spectrum associated with the 5T2 to or from 1A1 transition is interpreted by a sign reversal of Vzz resulting in Vzz(5T2)>0. Debye-Waller factors were determined from the saturation corrected areas of the Mossbauer spectra for the 5T2 and 1A1 ground states, individually. The values of -lnf5T2 and -lnf1A1 are well reproduced by the Debye model between 175 and 250K ( Theta 5T2=126.2K) and between 105 and 222K ( Theta 1A1=150.2K) respectively.