Magnetic properties of Antarctic stony meteorites Yamato-74115 (H5), -74190 (L6), -74354 (L6), -74362 (L6), and -74646 (LL6)

The thermomagnetic analysis of five Antarctic chondrites (Yamato-74115 (H5), -74190 (L6), -74354 (L6), -74362 (L6) and -74646 (LL6)) to determine the chemical composition of their metallic components are carried out, together with their magnetic analysis based on the magnetic hysteresis curves at room temperature, for the purpose of a comparison with the results of optical and microprobe analysis of the same chondrites performed by NAGAHARA (Mem. Natl Inst. Polar Res., Spec. Issue, 15,77,111,1979). In the Ni-content distribution spectrum in metals obtained by the magnetic analyses (magnetic spectrum), the metallic component consists of α-phase (kamacite) and (α+γ)-phase (plessite) in Yamato-74115,-74354 and -74646,while it consists of α-, (α+γ)- and γ-phases in Yamato-74190 and of α-, α_2- and (α+γ)-phases in Yamato-74362. In the occurrence frequency spectrum of average Ni-content in individual metallic grains obtained by the microprobe analysis (microprobe spectrum), it is shown that both α- and (α+γ)- or γ-phases are contained in a number of individual single metallic grains in Yamato-74115,-74354 and -74362. No α-phase is detected in the microprobe spectra of Yamato-74190 and -74646,whereas the major phase of metal in Yamato-74190 is the α-phase of 7 wt% Ni and Yamato-74646 also contains a small amount of α-phase in the magnetic spectra. The agreement and disagreement between the two kinds of spectrum can give rise to an overall view of both chemical composition and structure of metallic component in the chondrites