MAGNETOOPTIC PROPERTIES AND EXCHANGE INTERACTION OF THE MACROSCOPIC FERRIMAGNET CO1-X-YTBX(EUS)(Y)

Polar Kerr-rotation spectra and hysteresis loops have been measured in Co1-x-yTbx(EuS)(y), with 0 less than or equal to x less than or equal to 0.21 and 0 less than or equal to y less than or equal to 0.21, and compared to the macroscopic ferrimagnet Co-1-y(EuS)(y) and to amorpho us Co1-xTbx. The measurements were taken at room temperature and at 7 K over a wide photon energy range of 1.1-4.6 eV in fields up to 2.77 T . The addition of Tb retains the phase-separated nature yielding a mat erial consisting of a Go-To matrix containing crystalline EuS precipit ate particles with about 2 nm diameter. Up to 8% To is substituted for Eu in the EuS phase. The Kerr rotations are rather small reaching -0. 25 degrees at room temperature and increasing to -0.85 degrees at 7 K, i.e., no optical enhancement is observed as in Co(EuS). This is most likely due to the much smaller size of the EuS crystallites. An ''s''- shaped feature in the Kerr-rotation spectra can be assigned to an Eu2 4f-->5d transition while a contribution from the Tb3+-4f states shows up as a decrease with increasing photon energies. At 7 K, the Tb and Eu magnetic moments are found to be parallel while the Co moment is be lieved to be antiferromagnetically exchange coupled to both. At room t emperature, the Co moment is dominating the To moment which is antifer romagnetically coupled as in Co1-xTbx. (C) 1996 American Institute of Physics.