Demagnetization Results and Compositions of Spinels

Three chips, ~ 1 cm in diameter and ~ 1 cm in height, were cut from each block sample. One specimen per block sample was alternating-field (AF) demagnetized using a Molspin AF demagnetizer. The other specimen was used for thermal demagnetization, in 40^oC steps from 80 to 600^oC using a Magnetic Measurements MMTD80 thermal demagnetizer. In addition to NRM, NRM* is also considered. NRM* is calculated by projecting the cumulative vector-difference curves towards the direction of initial NRM. Supplementary excel file includes all the observed 20 demagnetization data. Nine representative results were displayed as Figures. To identify the magnetic phases, microscopic experiments were carried out on the third specimen using scanning electron microscopy (SEM) and electron microprobe. For microscopic analysis, we used a field emission scanning electron microscope JSM7000F and Cameca SX100 electron probe x-ray micro analyzer. For quantitative analysis, 2 minute peak countings and 1 minute background countings were obtained in an accelerating voltage of 15-20 kV, 10 nA beam current, and 1 µm spot size. Metals are represented as bright contrast in all the images used in the present article because back-scattered SEM photography is used. Compositional data were determined by stoichiometric calculations using the equations of Barnes and Roeder (2001). All the compositional data used for this study is provided as supplementary documentary Tables.