IR-dichroism of magnetic tapes: measurements with polarized IR-light

In measuring magnetic tapes in a transmission mode with linearly polarized IR light, it was observed that many magnetic layers show an IR dichroism in the wavelength region of 2.5 μm to 25 μm. The IR dichroism is mainly caused by the orientation of the magnetic particles in the tape. The degree of polarization rises with increasing thickness and increasing orientation factor of the magnetic layers. The IR dichroism (quantified as the degree of polarization) is pronounced in CrO₂ tapes, whereas tapes with Co-modified γ-Fe₂ O₃ show far less IR dichroism. By variation of the layer thickness and the orientation factor, calibration relations are obtained. With these calibration relations, the IR dichroism of magnetic tape is described semiempirically. It is concluded that detailed knowledge of the IR dichroism is the basic requirement for obtaining IR absorption spectra of magnetic layers without obstructions caused by interference patterns