a Typical Allende sample analyzed. b First-order reversal curve (FORC, a measure of magnetic interaction Hu versus microcoercivity Hc) showing large interactions (correspondingly large spread of Hu values; compare with ideal single domain case (Supplementary Fig. 1b) where Hu is restricted and the central FORC peak is more than order of magnitude greater than that seen in Allende data). For FORC parameters, see Supplementary Fig. 2. c Magnetic susceptibility versus temperature in an Ar atmosphere. VT, Verwey transition; mag, magnetite. d Magnetic susceptibility cycling at successively higher temperatures measured in an Ar atmosphere. Red: heating, Blue: cooling. e Partial thermal remanent magnetization (pTRM) between 292 °C and room temperature (i, iii, v, vii) followed by demagnetization (ii, iv, vi, viii). All experiments conducted in an Ar atmosphere. Red horizontal line: predicted values. f Orthogonal vector plot of demagnetization of remanence acquired after cooling from 340 °C in a reversing applied magnetic field (polarity changes illustrated by bar chart). Field applied along z axis; Red: inclination. Blue: declination. Experiments in Ar; temperature labels are ∘C. Interval of medium temperature component (MT) interpreted in prior work as holding a primary remanence highlighted. g Backscatter scanning electron microscope image; red box show enlargement area (h). Arrows highlight exsolution textures. h Energy dispersive spectroscopy analyses: i. Fe-sulfide, ii. Fe-Ni sulfide and iii. Ni-Fe metal.