ANTIFERROMAGNETIC COUPLING IN FE/CU/FE AND CO/CU/CO MULTILAYERS ON CU(111)

The magneto-optical Kerr effect has been used to investigate the exchange coupling between Fe and Co bilayers through Cu spacer layers. The films were grown on a Cu(111) substrate by molecular-beam-epitaxy (MBE) techniques under a variety of conditions, including both high vacuum and ultrahigh vacuum, substrate temperatures of 80, 300, and 500 K, and in the presence of as well as in the absence of electron bombardment. None of these films showed consistent evidence of antiferromagnetic (AFM) coupling, and there was no evidence of any consistent trends attributable to oscillatory AFM coupling. These results stand in marked contrast to results recently reported on similar multilayers that were grown by magnetron sputtering methods and that exhibit the giant magnetoresistance effect. These magnetron-grown multilayers, which are reported to be (111) textured, exhibit pronounced oscillatory AFM coupling. One possible resolution of these conflicting observations lies in the fact that oscillatory AFM coupling does occur in MBE-grown multilayers on Cu(100). Preliminary x-ray-diffraction polefigure measurements on three of the magnetron-grown multilayers indicate that the tendency to (111) texture is not very strong, and that the multilayers contain crystalline grains other than (111). Thus, the AFM coupling that these multilayers exhibit could be at least partly a result of a minority constituent of crystalline grains oriented at or near (100). However, it cannot be proven that the near-(100) grains are entirely responsible for the AFM coupling in the magnetron-grown multilayers. Grains of other orientation may also contribute, but surprisingly, the present work implies that the (111)-oriented grains do not contribute.