On the experimental determination of a ferromagnetic surface layer in antiferromagnetic chromium

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Abstract
The existence of a ferromagnetic surface layer in antiferromagnetic chromium has been confirmed experimentally by detecting surface magnetoplasma waves (SMPW) via the method of attenuated total reflection. The optical configuration consisted of a half cylinder heavy dense flint prism −900 Å MgF2 dielectric thin film–optically opaque chromium film. The dispersion curve for surface plasma waves (SPW) was obtained by measuring the reflectivity as a function of angle of incidence at constant photon energy in the range of 2.0–4.0 eV. Measurement of the normalized reflectivity difference δ due to a low frequency oscillating magnetic field applied perpendicular to the direction of propagation of the SPW indicates the presence of SMPW and therefore a ferromagnetic surface layer. Experimentally δ maximizes at E=3.25 eV and varies linearly with the applied magnetic field to 500 Oe. In the absence of SPMW δ is less than 1% of the δ measured in the presence of SMPW in the same photon energy range.