Coupling effects between ferromagnetic films of EuO and Fe in direct contact were studied in the temperature range 6 to 3000K by magnetooptic means. Thin Fe film (435 A) was vacuum evaporated onto heated glass substrates, followed by Eu0 films with several steps of thickness (350–1400 A). A strong antiparallel coupling is found. When the samples are cooled from room temperature to 10°K with the Fe film saturated, the two magnetizations are found to be 180’ apart. If the magnetizations are forced to be parallel by an external field, then subsequent switching occurs by coupled rotation in opposite senses; that is, the magnetization components along the driving field are parallel and the transverse components are antiparallel. The details of the composite hysteresis loops can be explained in terms of the effective field acting within each film due to the coupling. Because of the coupling, the switching field of the composite film can be reduced to 25 Oe, which is much lower than either film alone. © 1969 IEEE. All rights reserved.