Magnetic Characterization of Geologic Materials with First-Order Reversal Curves

Since their introduction in Earth sciences in 1990, first-order reversal curve (FORC) measurements have become an important tool for characterizing geologic materials. The visualization of irreversible magnetic processes, such as transitions between magnetic states in individual crystals, in a two-dimensional map provides a unique tool for discriminating complex mixtures of magnetic particle assemblages according to their composition and size, thereby reducing the intrinsic non-uniqueness of simpler magnetic characterization tools. The use of FORC measurements in Earth sciences has rapidly evolved, both technically (e.g., measurement resolution, data processing) and theoretically. For instance, numerical unmixing techniques have been recently implemented on FORC measurements (FORC-PCA), and micromagnetic calculations are now used to model the FORC signature of specific magnetic particle assemblages. The scope of this work is to provide, for the first time, a didactic and comprehensive review of FORC diagrams and their application in Earth sciences which includes (1) the theoretical foundations; (2) the connection with Preisach theory and with other magnetic characterization tools; (3) detailed instructions for optimal planning, execution, and processing of FORC measurements; and (4) an in-depth analysis of the fundamental FORC signatures commonly occurring in rocks and sediments.