Physics of Magnetism

(^136) CHAPTER 13. HIGH-DENSITY RECORDING MATERIALS
a small angle when the light is reflected by a magnetic layer. This rotation of the
polarization plane depends on the direction of the magnetization, that is, it is in opposite
directions for regions having an opposite magnetization direction. The written bits can
then be distinguished from the matrix region by means of Nichol prisms (or Mylar foils).
An example of magnetic domains written and read-out using an amorphous Gd–Fe film is
shown in Fig. 13.2.3.
If the substrate is translucent and the amorphous film is sufficiently thin, one may use
transmitted, linearly polarized light to read out the written bits. Also, in this case there will
be a rotation of the polarization plane (Faraday effect). The advantage of transmitted
light is that the rotation angle increases with the thickness of the magnetic layer. This
offers a better possibility of optimizing the contrast between written bits and the matrix,
bearing in mind that the film is no longer translucent if it becomes too thick. A more detailed
description of magneto-optical recording devices and materials can be found in the reviews
of Buschow (1984), Reim and Schoenes (1990), and Hansen (1991).
It is interesting to discuss briefly the temperature dependence of or Results
obtained on several amorphous films are shown in Fig. 13.2.4. These results
have to be compared with the temperature dependence of the magnetization, shown for a
number of such alloys in Fig. 13.2.1. It follows from the results of the latter figure that
there is a compensation temperature in the temperature dependence of the magnetization
of the amorphous alloys when the Fe concentration falls into the range
Inspection of the results shown in Fig. 13.2.4 makes it, however, clear that such
features are absent in the temperature dependence of the Faraday rotation. This means that