Ferromagnetic and paramagnetic resonance spectra of lunar material: Apollo 12

Abstract

Electron magnetic resonance spectra of specimens of two crystalline rocks (12021-55 and 12075-19) and of four specimens of fines < 1 mm (12001-16, 12030-16, 12033-50 and 12070-125) have been obtained as a function of spectrometer frequency (9 and 35 GHz), temperature (78 to 300K), heat treatments (to 960°C), and mineral phases (plagioclase, olivine, pyroxferroite, glass, and basaltic fragments). Three paramagnetic ions, Fe3+, Ti3+ and Mn2+, are identified on the basis of spectral characteristics in plagioclase fractions, with concentrations ⩽ 1019 ions g−1. Spectral components of at least two phases with exchange coupling of unpaired spins are resolved in ‘whole’ rock samples of the crystalline rock specimens. These disappear upon heat treatment in air at 250°C and are presumably the result of an oxidation of the phases. It is suggested that these are non-stochiometric iron-rich oxide phases which approach stochiometry with heating in air. Some of the spectral properties of the ‘characteristic’ resonance in fines are shown to be inconsistent with the hypothesis that the resonance is due to spherical iron particles. Another intense spectral component observed in samples of 12033-50 (ΔH ~ 3000 Oe,g ~ 4 at 9 GHz andΔH ~ 3000 Oe,g ~ 2.2 at 35 GHz) is also observed in basaltic appearing fragments selected from 12001-16. It is estimated that the source of this component has concentrations in 12001-16, 12030-16, and 12075-125 that are < 2% the concentration in 12033-50. A similarity of this component to one observed in a crystalline rock sample from 12021-55 heat-treated in air and then left in air for 27 days and to one observed in a sample of fines heat treated at low pressure (< 10−3 mm Hg) to 800°C is the basis for suggesting that it is also due to a ferromagnetic oxide phase. The spectrum of a ferromagnetic metal platlet from 12001-16, in which the resonance and antiresonance were well resolved, was used to calculate the saturation magnetization and gave a value in reasonable agreement with that of iron as expected.