Effects of mechanical grinding on magneto-structural properties of BaFe12O19 powders

The structural and magnetic properties of deformed powders of M-type Baferrite, obtained by mechanical grinding, have been investigated using X-ray diffraction, Mössbauer spectroscopy, thermomagnetic analysis, and magnetic measurements. The rapid decrease in the magnetization after short grinding times in air is attributed to the formation of a phase which is paramagnetic at room temperature but at 150 K the phase behaves like a spin-glass, with antiferromagnetic short-range order. From Mössbauer spectra this phase has at least five non-equivalent sites of iron with hyperfine interaction field values Hrf(77 K): H1=38.69; H2=37.01; H3=36.14; H4= 34.31 and H5=30.96 MA/m, and a magnetic moment ?Fe = 2.1?B. At longer grinding times the deformed BaFe12O19 samples were found to be thermodynamically unstable and decomposed partially into ?-Fe2O3 and Fe3O4.