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The technique of transient enhancement of initial ac susceptibility is introduced. The time dependence of the low-field ac susceptibility of ferromagnets is observed in the presence of a second time-varying field. The technique enables the diffusion of domain-wall pinning centers to be studied and also acts as a sensitive indicator of domain nucleation for magnetic critical-phenomena studies near the Curie temperature. Preliminary results for ferromagnetic gadolinium over the temperature range 240-292 K yield an activation energy for the pinning centers of ~0.7 eV.

The material parameters that are important in the detection of thermal radiation by means of the Nernst effect are first considered. Then a simple treatment of the thermomagnetic properties of an aligned two-phase system is given and applied to eutectics based on the semiconductor Cd3As2. The results of experiments on radiation detection using the Cd3As2-NiAs eutectic are reported. These results indicate that the NiAs concentration is too small to have any beneficial effect other than that of giving added mechanical strength. Nevertheless it appears that a Cd3As2-NiAs detector operating at room temperature in a magnetic field of 0·7 tesla is about three times as sensitive as one made from InSb-NiSb having the same electrical resistance and response time.

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