INFLUENCE OF THE GROWTH TECHNIQUE ON THE COUPLING AND MAGNETORESISTANCE OF CO RU SANDWICHES/

A comparative study of the structure and magnetotransport properties o f Co/Ru sandwiches grown by evaporation in ultrahigh vacuum (UHV) and by plasma sputtering is reported. The crystalline structure of both ty pes of samples has been studied by x-ray diffraction and transmission electron microscopy and the interfacial morphology by nuclear magnetic resonance, The comparison shows that the main structural difference c omes from the crystalline quality: the evaporated samples are single c rystals whereas the sputtered samples are polycrystalline and not text ured. This difference in structure has no significant effect on the ma gnetoresistance, which is small for both growth techniques and is attr ibuted to the strong interfacial mixing observed in both cases. The cr ystalline quality has a stronger effect on the exchange coupling. Inde ed, its strength is more than a factor of 2 larger in the UHV samples than In the sputtered ones. Moreover, we observe that the shape of the room-temperature coupling oscillations obtained with the UHV samples is in good agreement with ab initio calculations. This indicates that the coupling is very homogeneous in those samples. Surprisingly the ag reement is still good at low Ru thicknesses where ferromagnetic bridge s are usually observed. This has been studied in more detail by temper ature-dependent magnetometry. It shows that the absence of ferromagnet ic bridges is due to the interfacial magnetization reduction (a conseq uence of the interfacial mixing), which prevents, at roam temperature only, the appearance of ferromagnetic bridges. [S0163-1829(98)03208-1] .