A Critical Appraisal of the “Day” Diagram

Abstract

The “Day” diagram (Day et al., 1977, https://doi.org/10.1016/0031-9201(77)90108-X) is used widely to make inferences about the domain state of magnetic mineral assemblages. Based on theoretical and empirical arguments, the Day diagram is demarcated into stable “single domain” (SD), “pseudo single domain” (“PSD”), and “multidomain” (MD) zones. It is straightforward to make the necessary measurements for a sample and to plot results within the “domain state” framework based on the boundaries defined by Day et al. (1977, https://doi.org/10.1016/0031-9201(77)90108-X). We discuss 10 issues that limit Day diagram interpretation, including (1) magnetic mineralogy, (2) the associated magnetocrystalline anisotropy type, (3) mineral stoichiometry, (4) stress state, (5) surface oxidation, (6) magnetostatic interactions, (7) particle shape, (8) thermal relaxation, (9) magnetic particle mixtures, and (10) definitional/measurement issues. In most studies, these variables are unknowns and cannot be controlled for, so that hysteresis parameters for single bulk samples are nonunique and any data point in a Day diagram could result from infinite combinations of relevant variables. From this critical appraisal, we argue that the Day diagram is fundamentally ambiguous for domain state diagnosis. Widespread use of the Day diagram has also contributed significantly to prevalent but questionable views, including underrecognition of the importance of stable SD particles in the geological record and reinforcement of the unhelpful PSD concept and of its geological importance. Adoption of approaches that enable correct domain state diagnosis should be an urgent priority for component‐specific understanding of magnetic mineral assemblages and for quantitative rock magnetic interpretation.

On the Reliability of Absolute Palaeointensity Determinations on Basaltic Rocks Bearing a Thermochemical Remanence

“…Figure shows the magnetic hysteresis loops of Samples P‐72/4 and ST‐1 at the initial state and at the end of the thermal treatment. Whereas these loops are consistent with the presence of a mixture of multidomain and pseudo single‐domain (PSD) particles at the initial state of the thermal treatment, they are characteristic of single‐domain (SD) and small PSD particles at the end of the thermal treatment (e.g., Roberts et al, ).…”

Domain State Diagnosis in Rock Magnetism: Evaluation of Potential Alternatives to the Day Diagram

“…(i) Day and (j) Néel diagrams for submarine basaltic glass (SBG) and extrusive rocks from the Azores Islands (Portugal), Mt St Helens (USA), Vesuvius (Italy), and Lascar (Chile). Hysteresis results for the various data sets have been discussed previously by Roberts et al (), Roberts, Tauxe, et al, ) with citation of source references. The region for USD + SP magnetite (Figure b) from Tauxe et al () is indicated on the respective Néel diagrams.…”

“…We, therefore, do not recommend routine use of the Day, Néel, Borradaile, and Fabian diagrams (Borradaile & Lagroix, ; Day et al, ; Fabian, ; Néel, ) unless they are used for pure magnetic mineral components. Reasons for this recommendation are provided by Roberts, Tauxe, et al (), where the focus is on the Day diagram, but most of the same issues also apply to the Néel and Borradaile diagrams. The Lascu diagram (Lascu et al, ) is also based on bulk parameters, but it is designed for use with extensive additional mineral magnetic information to constrain interpretation.…”

“…Many difficulties with Day diagram interpretation have long been known. Roberts et al () recently presented a comprehensive critical appraisal of the Day diagram and pointed to 10 sets of issues that produce uncontrolled unknowns that limit its use for domain state diagnosis, so that hysteresis parameters for single bulk geological samples are usually nonunique in terms of domain state interpretations.…”

“…Illustration of the domain state diagnosis methods evaluated in this paper. (a) The Day diagram (Day et al, ) with regions for SD, PSD, and MD behavior, which has been argued to be fundamentally ambiguous (Roberts, Tauxe, et al, ) and for which alternatives must be found. (b) The Néel diagram (Néel, ) with a slightly modified interpretive framework provided by Tauxe et al ().…”