EFFECTS OF MECHANICAL GRINDING ON MAGNETOSTRUCTURAL PROPERTIES OF BAFE12O19 POWDERS

The structural and magnetic properties of deformed powders of M-type B aferrite, obtained by mechanical grinding, have been investigated usin g X-ray diffraction, Mossbauer spectroscopy, thermomagnetic analysis, and magnetic measurements. The rapid decrease in the magnetization aft er short grinding times in air is attributed to the formation of a pha se which is paramagnetic at room temperature but at 150 K the phase be haves like a spin-glass, with antiferromagnetic short-range order. Fro m Mossbauer spectra this phase has at least five non-equivalent sites of iron with hyperfine interaction field values H-hf (77 K): H-1 = 38. 69; H-2 = 37.01; H-3 = 36.14; H-4 = 34.31 and H-5 = 30.96 MA/m, and a magnetic moment mu(Fe) 2.1 mu(B). At longer grinding times the deforme d BaFe12O19 samples were found to be thermodynamically unstable and de composed partially into alpha-Fe2O3 and Fe3O4.