Fig. 7

Day plots of the measured and compiled hysteresis parameters. a Day plot (Day et al. 1977) of the measured hysteresis parameters (black circles). Numbers correspond to those in Table 2. Nos 5 and 7 are tephra C and A, respectively. SD, PSD and MD shown in blue are domain states corresponding to magnetite. Blue curves and numbers are two SD-MD mixing curves and mixing ratios (Dunlop et al. 2002). b Day plot of the parameters for the measured samples (black circles) together with that for greigite bearing marine sediments around New Zealand (Roberts et al., 2011). Red curves are mixing curves of SD with 5 nm and 10 nm SP particles and with mixing ratios (Dunlop et al. 2002). c Day plot for framboidal greigite based on micromagnetic simulations (replotted from Valdez-Grijalva et al. 2020). Open circles are non-interacting grains of different sizes (the left most circles and the right most circles correspond to 30 nm and 100 nm, respectively). An open rectangle is a framboid with 30 nm particles. Upward-pointing and downward-pointing triangles are mixtures of framboids with isolated SD grains and isolated SV (single vortex) grains, respectively. The mixtures contain increasing proportions of SD and SV material from 10 to 100% with grain size contributions of 30–48 nm and 70–80 nm