EXCHANGE-COUPLING ACROSS SIO

Strongly temperature-dependent ferromagnetic exchange coupling is observed between Fe films separated by an amorphous SiO barrier. Heating reversibly enhances the coupling strength which monotonically decreases with increasing SiO thickness. At T = 40 K the coupling disappears for d(SiO) approximate to 20 Angstrom whereas at room temperature it persists up to a barrier thickness of 60 Angstrom, The coupling strength J is determined by externally compensating the exchange field of samples grown on an antiferromagnetically biased Fe/Cr/Fe structure, It amounts to J approximate to 2 . 10(-6) J/m(2) for a sample with d(SiO) = 25 Angstrom at T = 300 K. As a tentative explanation we propose that impurity or defect states within the large mobility gap of SiO carry the magnetic interaction across the insulating barrier.