Magneto-optic Kerr effect in CoFe2−xMxO4 (M=Mn, Cr, Al) and BaFe12−2x–COxTixO19 with tetrahedrally coordinated Co2+

Polar Kerr effect has been observed at λ=0.4–2.0 μm on hot-pressed ceramics of Co2+Fe3+2−xM3+xO4 (M=Mn, Cr, Al, 0≤x≤1.2) and BaFe3+12−2x–Co2+xTi4+xO19 (0≤x≤1.5), in which tetrahedrally coordinated Co2+ ions [Co2+(Td)] increase with x. To avoid effect of birefringence in the hexagonal ferrite, ceramics with prefered orientation along the c axis have been prepared by a topotaxial reaction technique. Enhancement in the Kerr effect associated with the crystal field transitions of Co2+ (Td) is observed at λ≊0.7 and 1.7 μm in both CoFe2−xMxO4 and BaFe12−2x–CoxTixO19, though the magnitude in the latter compound is several times smaller than in the former. The large normal remanence observed by surface Kerr effect in CoFe2−xMxO4 can not be attributed to the residual stress induced by hot-pressing as has been pointed out previously.