Magnetic Ordering at 4.2 and 1.3 K in Nontronites of Different Iron Contents: A 57Fe Mössbauer Spectroscopic Study

C. M. Cardile1, 3, J. H. Johnston1 and D. P. E. Dickson2
1 Chemistry Department, Victoria University of Wellington, Private Bag, Wellington, New Zealand
2 Department of Physics, The University of Liverpool, Liverpool, United Kingdom
3 Present address: Chemistry Division, Department of Scientific and Industrial Research, Private Bag, Petone, New Zealand.

Abstract: The 57Fe Mössbauer spectra of six nontronite samples were measured at appropriate temperatures of 4.2 and 1.3 K. Three of the nontronites gave a complex magnetic hyperfine spectrum showing magnetic ordering at 4.2 K, and the other three required a lower temperature of 1.3 K to produce similar magnetic ordering. The spectra were computer-fitted with three closely overlapping sextets which are considered to arise from: (1) Fe3+ that is ordered magnetically in the cis-octahedral sites with a greater number of neighboring tetrahedral Fe3+ ions (51 T); (2) the cis-octahedral site with the greater number of neighboring Si4+ ions (46 T); and (4) the tetrahedral sites (41 T). In an untreated sample a further sextet corresponding to interlayer Fe3+ (36 T) was identified. The magnetic ordering was complicated and not directly related to the iron content of these sites. It probably depended also on the overall composition and structural order of the particular nontronite. The ordering appears to have been essentially two-dimensional, consistent with the layer structure of this material.

Key Words: Interlayer site • Iron • Magnetic ordering • Mössbauer spectroscopy • Nontronite • Octahedral site • Tetrahedral site

Clays and Clay Minerals; June 1986 v. 34; no. 3; p. 233-238; DOI: 10.1346/CCMN.1986.0340302
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)