MAGNETIC ORDER IN CERTAIN ALKALI AMPHIBOLESA MÖSSBAUER INVESTIGATIONReport as inadecuate




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Abstract : The appearance of magnetic hyperfine splitting mhfs has been used to determine the magnetic ordering temperature for a few selected alkali amphiboles. This class of minerals has the monoclinic crystal structure and the general formula Na, Ca2-3Fe+2, Fe+3, Mg, Al5Si8O22OH, F2. The iron can occupy three distinct crystallographic sites, yet the mhfs collapses with increasing temperature in the manner of less complex magnetic substances. In spite of the overall complexity, the much greater mhfs of Fe+3 easily separates lines 1 and 6 from all resonant absorption due to Fe+2. Thus, relevant Mössbauer and magnetic parameters can be determined. The temperature dependence of the mhfs departs substantially from the usual Brillouin-like function. Magnetic susceptibility data on a single specimen indicates the ordering to be antiferromagnetic. The stacking sequence formed by the three sites is a one-dimensional chain parallel to the c axis. Each chain is separated from adjacent chains by linked SiO4 tetrahedra. Thus, direct exchange can only occur within the chain, and a type of super-exchange must exist between chains.





Author: R. Borg I. Borg

Source: https://hal.archives-ouvertes.fr/



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