| The Mossbauer spectra of a basalt glass containing about 13 wt %
Fe,O., which forms magnetite on heat-treatment, have been studied
both at 300 K and at 4 K and without magnetic field. The observed
magnetic hyperfine splitting at 300 K is related to the anisotropy of
the magnetite particles having a particle size higher than a critical
value. The observed hfs pattern at 4 K with H = 0 in the Mossbauer
spectra is found to be independent of the particle size. The Mossbauer
spectra at 4 K with H # 0 show that the Llmr = 0 lines do not
disappear in the magnetite particles below the critical size, while
above the critical size, these lines disappear with the progressive
application of the magnetic field applied parallel to the y-ray direction.
The above results are represented in terms of a model of magnetic
structure of the small particles of magnetite embedded in a
glassy matrix. |
