Quantitative interpretation of the magnetic susceptibility frequency dependence

Author(s)

Ustra, Andrea ^[1] ; Mendonca, Carlos A. ^[1] ; Leite, Arua ^[1] ; Jovane, Luigi ^[2] ; Trindade, Ricardo I. F. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Astron Geophys & Atmospher Sci, Dept Geophysics, Rua Matao 1226, BR-05508090 Sao Paulo, SP - Brazil

^[2] Univ Sao Paulo, Oceanog Inst, Praca Oceanog 191, BR-05508120 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: Geophysical Journal International; v. 213, n. 2, p. 805-814, MAY 2018.
• Web of Science Citations: 1

Abstract

Low-field mass-specific magnetic susceptibility (MS) measurements using multifrequency alternating fields are commonly used to evaluate concentration of ferrimagnetic particles in the transition of superparamagnetic (SP) to stable single domain (SSD). In classical palaeo-magnetic analyses, this measurement serves as a preliminary assessment of rock samples providing rapid, non-destructive, economical and easy information of magnetic properties. The SP-SSD transition is relevant in environmental studies because it has been associated with several geological and biogeochemical processes affecting magnetic mineralogy. MS is a complex function of mineral-type and grain-size distribution, as well as measuring parameters such as external field magnitude and frequency. In this work, we propose a new technique to obtain quantitative information on grain-size variations of magnetic particles in the SP-SSD transition by inverting frequency-dependent susceptibility. We introduce a descriptive parameter named as `limiting frequency effect' that provides an accurate estimation of MS loss with frequency. Numerical simulations show the methodology capability in providing data fitting and model parameters in many practical situations. Real-data applications with magnetite nanoparticles and core samples from sediments of Poggio le Guaine section of Umbria-Marche Basin (Italy) provide additional information not clearly recognized when interpreting cruder MS data. Caution is needed when interpreting frequency dependence in terms of single relaxation processes, which are not universally applicable and depend upon the nature of magnetic mineral in the material. Nevertheless, the proposed technique is a promising tool for SP-SSD content analyses. (AU)

• FAPESP's process: 16/06114-6 - The Neoproterozoic Earth System and the rise of biological complexity
• Grantee: Ricardo Ivan Ferreira da Trindade
• Support Opportunities: Research Projects - Thematic Grants