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Superparamagnetism in volcanic glasses of the KBS Tuff: Transmission electron microscopy and magnetic behavior
Author(s) -
Schlinger Charles M.,
Smith Rebecca M.
Publication year - 1986
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl013i008p00729
Subject(s) - superparamagnetism , magnetite , transmission electron microscopy , volcano , materials science , magnetic susceptibility , mineralogy , condensed matter physics , volcanic glass , magnetization , chemical physics , geology , magnetic field , nanotechnology , volcanic rock , geochemistry , chemistry , metallurgy , physics , quantum mechanics
Volcanic glass separates (colorless to dark brown) from the KBS tuff of northern Kenya have been studied with a combination of transmission electron microscopy and low‐temperature ac susceptibility and dc magnetization experiments. The darker of these glasses exhibit classic superparamagnetic behavior, the origin of which lies in a spatially‐uniform precipitate of magnetite, which is present as ∼1% by weight in glass shards with the highest susceptibility. In any given glass separate (obtained by magnetic separation) this precipitate has a surprisingly narrow size distribution. A theory for the origin of the precipitate is nucleatation and growth in quenched glasses at temperatures of ∼1000‐1300°K; an experiment demonstrates the feasibility of this idea. These glasses provide us with a sample for experimental investigations of physical properties of naturally‐occurring dispersed magnetic phases at the lower limit of physical dimension that can be attained in the crystalline state.