Domain state diagnosis in rock magnetism: evaluation of potential alternatives to the Day diagram

The Day diagram is used extensively in rock magnetism for domain state diagnosis. It has been shown recently to be fundamentally ambiguous for 10 sets of reasons. This ambiguity highlights the urgency for adopting suitable alternative approaches to identify the domain state of magnetic mineral components in rock magnetic studies. We evaluate 10 potential alternative approaches here and conclude that four have value for identifying data trends, but, like the Day diagram, they are affected by use of bulk parameters that compromise domain state diagnosis in complex samples. Three approaches based on remanence curve and hysteresis loop unmixing, when supervised by independent data to avoid nonuniqueness of solutions, provide valuable component‐specific information that can be linked by inference to domain state. Three further approaches based on first‐order reversal curve diagrams provide direct domain state diagnosis with varying effectiveness. Environmentally important high‐coercivity hematite and goethite are represented with variable effectiveness in the evaluated candidate approaches. These minerals occur predominantly in noninteracting single‐domain particle assemblages in paleomagnetic contexts, so domain state diagnosis is more critical for ferrimagnetic minerals. Treating the high‐coercivity component separately following normal rock magnetic procedures allows focus on the more vexing problem of diagnosing domain state in ferrimagnetic mineral assemblages. We suggest a move away from nondiagnostic methods based on bulk parameters and adoption of approaches that provide unambiguous component‐specific domain state identification, among which various first‐order reversal curve‐based approaches provide diagnostic information