MAGNETIC BEHAVIOR OF FESIO3-MGSIO3 ORTHOPYROXENE SYSTEM FROM NGR IN 57FE

The magnetic behavior of (FexMg1-x)SiO3 with 0.269≤x≤1.0 was investigated between 300° and 1.7°K using NGR of 57Fe. For x≳0.76 magnetic ordering was observed at the following temperatures: x=1.0, TC=38°K; x=0.866, T C=18°K; x=0.758, TC=11°K. Ferrous ions occupy two different lattice sites (M1 and M2) of low symmetry. The resonance spectra consist of two superimposed hyperfine patterns, which reflect different electronic ground states for Fe2+ at the two sites. The M2 site is characterized by a smaller magnetic hyperfine field and a more negative isomer shift compared to the M1 site. Typical values for FeSiO3 at 4.2°K are 113 kOe, 1.29 mm/sec, 45 MHz at M 2 and 290 kOe, 1.34 mm/sec, 69 MHz at M1. Above T C two quadrupolar doublets are observed. The quadrupole coupling of the M1 site shows a strong temperature dependence, while that of the M2 site remains fairly constant. The magnetically more dilute samples (x≲0.4) did not show ordering in the temperature region above 1.7°K, but produced paramagnetic relaxation spectra with only the smaller of the two hyperfine fields present, since only the M2 site is occupied sufficiently with Fe2+ for the resonance to be observed. © 1969 The American Institute of Physics.