An investigation of the low-temperature Faraday rotation spectrum of BaFe12O19

The Faraday rotation spectra between 1.5 eV and 2.4 eV are examined for thin films of the hexagonal ferrite BaFe12O19, prepared by pulsed laser deposition. Fine spectral detail is observed at 24 K between 1.69 eV and 1.85 eV. A sharp paramagnetic transition at 1.69 eV, with an oscillator strength of 5 x 10(-2), is assigned to the (6)A(1g)(S-6) --> T-4(2g)((4)G) crystal field transition originating on the 4f(2) octahedrally coordinated Fe3+ site. Somewhat weaker diamagnetic transitions above 1.73 eV are tentatively assigned to first-excited-state transitions in the 2b trigonal bipyramidal Fe3+ site. A broader feature with an extremum at 2.23 eV is considered to originate from the (6)A(1)(6S) --> T-4(2)((4)G) transition in 4f(1) tetrahedral sites.