OPTICAL-ABSORPTION ANOMALIES NEAR MAGNETIC PHASE-TRANSITIONS IN COPPER-OXIDE

The optical absorption coefficient in the region of a wide charge-tran sfer band in copper oxide CuO ((h) over bar omega=3.19 eV) exhibits sh arp and anomalously large (up to 8% (!)) changes near two magnetic pha se transition temperatures (T(N1)approximate to 213 K and T(N2)approxi mate to 230 K) is shown that the wide fundamental absorption bands can be used for optical detection of magnetic phase transitions, the para meters of long- and short-range magnetic order, and the effects of a m agnetic-impurity state. (C) 1996 American Institute of Physics.