Status of Magneto-optical Experiments on Ordered Rare Earth Compounds

Rare-earth compounds of interest in this field have ordering temperatures typically in the range 1°−4°K. This in turn implies internal fields of order 10 kOe, and therefore a potentially amenable experimental situation. A number of such systems have been studied recently, where the magneto-optic effects due to the magnetic order have been studied for both the host rare-earth ion, and for small amounts of other rare-earth ions introduced as probes into the systems. The following are some of the general conclusions to be drawn from this work: (i) the relative sucess of a ``one-ion''-essentially molecular field-picture in explaining effects observed both as a function of temperature and as a function of externally applied field, (ii) the considerable difference between effects seen by host ions and effects seen by probe ions, (iii) observation of magnetic effects at temperatures above the ordering temperature, therefore attributable to magnetic short-range order in the system, and (iv) the considerable difference in detail between short-range-order effects seen in different systems.