We have studied the growth and magnetic properties of molecular beam epitaxy grown layers of bcc Fe(001) on MgO(001) substrates at a wide range of temperatures. For growth temperatures in the range 80−595 K, the iron forms islands which increase in lateral size with increasing temperature. Completed films in the same temperature range show the magnetic properties expected for a system with biaxial anisotropy, and a coercivity of <10 Oe. The value of the first cubic anisotropy constant divided by the magnetization (K1/M) remained constant. No evidence for uniaxial magnetic anisotropy in the films was found. Above 595 K, the films’ structure and magnetic properties changed dramatically to those characteristic of a particulate system.

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Thin films of (La1−xCax)MnO3 prepared by laser ablation deposition are ferromagnetic when 0.2≤x≤0.5 with Tc≊250 K. These films show strong Faraday rotation both in the vicinity of the 2p(O)→3d(Mn) charge-transfer absorption at approximately 3.0 eV (θF≳40 000°/cm), and in the vicinity of the 3d(t2g)→3d(eg) excitation at approximately 1.5 eV (θF≳10 000°/cm just below Tc). The films are moderately transparent, having values of 2θF/α of approximately 0.1 at 1.5 eV and 0.5 at 3.0 eV.

Magnetic properties of a new family of ternary rareearth iron nitrides R2Fe17N3−δ (invited)The reaction between nitrogen gas and the series of R, Fe,, intermetallic compounds is studied by thermopiezic analysis on micron-size powders. Nitrogen diffusion in the range 300-550 "C can be represented by an activated interstitial diffusion process D = Doe-Em'kT with Do = 1.95 X 10 -lo m2 s -' and an activation energy E,,, = 0.8 1 eV. This stage of the nitrogenation reaction leads to the formation of R, Fe,, N, _ 6 nitrides which have structures related to those of the parent compounds. Heating above about 800 "C leads to complete disproportionation of the compounds into a mixture of rare-earth nitride and iron.

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