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Time‐dependent IRM: A new technique for magnetic granulometry
Author(s) -
Worm HorstUlrich
Publication year - 1999
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 - 10.1029/1999gl008360
Subject(s) - remanence , maghemite , granulometry , magnetite , diamagnetism , superparamagnetism , saturation (graph theory) , materials science , coercivity , mineralogy , analytical chemistry (journal) , single domain , geology , nuclear magnetic resonance , condensed matter physics , hematite , magnetic field , magnetization , chemistry , magnetic domain , physics , chromatography , paleontology , mathematics , quantum mechanics , combinatorics , sediment , metallurgy
The intensities of isothermal remanent magnetizations (IRM) acquired in 0.01 s and 10 s can differ by more than an order of magnitude depending on field strength and sample composition. For 15 samples containing magnetite, titanomagnetite, maghemite, hematite or pyrrhotite of distinct grain sizes, ranging from superparamagnetic (SP) over stable single domain (SSD) to multidomain (MD) behavior, the IRM acquisition has been meas‐ured for the two time constants. In addition, the viscous decay following IRM acquisition within 2000 s has been determined. In low fields (≤10 mT) the IRM(10s)/IRM(0.01s) ratios range from 1.03 for MD grains up to >20 for SP/SSD grains. For fields larger than the coercivity of remanence the IRM ratio approaches unity for all samples. Viscous decay after IRM acquisition is for samples containing SP grains much larger than for SSD and MD grains as well. Hence, a viscous decay parameter S d = (IRM to −IRM t )/log(t/t o ) normalized by the saturation remanence can serve as an alternative to the frequency dependence of susceptibility, the commonly used proxy for SP grains. In feet, it may be more sensitive because remanences cannot be masked by para‐ or diamagnetic contributions and IRMs can well be measured on weakly magnetic sediments.