Magnetic behavior of trioctahedral micas with different octahedral Fe ordering

• Published in: Physics and chemistry of minerals Vol. 39; no. 8; pp. 665 - 674
• Main Authors: Pini, Stefano, Brigatti, Maria Franca, Affronte, Marco, Malferrari, Daniele, Marcelli, Augusto
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-09-2012; Springer Nature B.V
• Subjects: Cations; Chemical composition; Crystallography and Scattering Methods; Earth and Environmental Science; Earth Sciences; Geochemistry; Magnetic fields; Magnetic permeability; Magnetic properties; Magnetic structure; Mineral Resources; Mineralogy; Organic chemistry; Original Paper; Spin glasses; Temperature dependence; XAS; Polylithionite; Siderophyllite; Crystal chemistry; Magnetic properties
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-012-0520-1

This contribution is finalized at the discussion of the magnetic structure of two samples, belonging to phlogopite–annite [sample TK, chemical composition
IV
(Si
2.76
Al
1.24
)
VI
(Al
0.64
Mg
0.72
Mn
0.03
Ti
0.15
) (K
0.96
Na
0.05
) O
10.67
(OH)
1.31
Cl
0.02
] and polylithionite–siderophyllite joints [sample PPB, chemical composition
IV
(Si
3.14
Al
0.86
)
VI
(Al
0.75
Mg
0.01
Mn
0.01
Ti
0.01
Li
1.09
) (K
0.99
Na
0.01
) O
10.00
(OH)
0.65
F
1.35
]. Samples differ for Fe ordering in octahedral sites, Fe
2+
/(Fe
2+
 + Fe
3+
) ratio, octahedral composition, defining a different environment around Fe cations, and layer symmetry. Spin-glass behavior was detected for both samples, as evidenced by the dependency of the temperature giving the peak in the susceptibility curve from the frequency of the applied alternating current magnetic field. The crystal chemical features are associated to the different temperature at which the maximum in magnetic susceptibility is observed: 6 K in TK, where Fe is disordered in all octahedral sites, and 8 K in PPB sample, showing a smaller and more regular coordination polyhedron for Fe, which is ordered in the
trans
-site and in one of the two
cis
-sites.