Faraday rotation measurements on ferrimagnetic oxides have so far been limited to single crystals which are rendered transparent by grinding. In the present studies films of NiFe20. and CoFe20. of thickness 1000-8000 ..t, suitable for optical studies are prepared by oxidizing films of the alloys NiFe2 and CoFe2 sputtered on silica substrates. The Faraday rotation is determined with the film magnetized along axes both normal and parallel to its surface. Using the latter arrangement, optical hysteresis loops are recorded and chec~ed against those obtained with a vibrating sample magnetometer. The dep~ndence of loop shape and coercive force on film thickness and oxidation temperature is studied.

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A systematic study was made of thin-film absorption at 2.8microm and 3.8 microm for a wide variety of transparent coating materials. The extinction and absorption coefficients were measured using HF/DF chemical laser calorimetry in single-layer films of PbF(2), LiF, YbF(3), NaF, ThF(4), As(2),S(3), As(2),Se(3), Si, MgO, ZnSe, and Al(2),O(3), on CaF(2), substrates. The lowest absorbing film materials were the As glasses, ZnSe, and some fluorides. In these cases, high-purity starting material led to the lowest loss films.