The magnetic and magnetotransport properties of several series of sandwiches consisting of two ferromagnetic layers (Ni, Co, Ni80Fe20) separated by a noble metal (Cu, Ag, Au) are described. In order to vary the relative orientation of the magnetizations of the two ferromagnets, one of them was constrained by exchange anisotropy (e.g., NiFe/Fe50Mn50). The ferromagnetic layers are magnetically soft and not coupled antiparallel, giving very large changes of resistance at low fields. At room temperature relative changes ΔR/R of 4.1% in 10 Oe for Si/Ta 50 A/NiFe 62 A/Cu 22 A/NiFe 40 A/FeMn 70 A/Ta 50 A and 8.7% in 20 Oe has been obtained for a structure based on Co/Cu/Co layers. The magnetoresistance versus the thickness of the ferromagnetic layer shows a broad peak near 80 A for Ni, Co and NiFe, demonstrating the importance of bulk rather than interfacial spin‐dependent scattering, in contrast to Fe/Cr multilayers. The magnetoresistance decreases exponentially with increasing interlayer (Cu and Au) thickness,...

Magnetotransport properties of magnetically soft spin‐valve structures (invited)

Spin waves in exchange-coupled epitaxial double-layers

We have used ferromagnetic resonance (FMR) at 33 GHz to study the properties of a number of evaporated thin Fe film systems. Values for effective anisotropy field HKeff , g value, and exchange constant A were derived. For Fe on glass, ‖HKeff ‖ was found to increase with increasing thickness. These changes were attributed to stress which decreased with film thickness. The presence of a Cu or a Ti underlayer did not seem to affect HKeff for films grown at room temperature. However, Fe/Ti/glass films made at higher substrate temperatures, Ts, did show an increase in ‖HKeff ‖. The appearance of a spin‐wave mode in the Fe films enables us to compute the exchange constant A for Fe, A=(2.12±0.14)×10−6 ergs cm−1. The coupling between two thin Fe films through an intervening Cu layer was investigated. A model predicting the number and position of the peaks in the spectrum as a function of coupling is presented. From experiment it was observed that the coupling remains almost constant through the 50–5‐nm Cu thickne...

FMR in evaporated single and multilayer thin Fe films

Brillouin light scattering from layered magnetic structures

The spinwave modes occurring in layered magnetic structures are discussed. Experimental examples obtained by means of light scattering are presented. Emphasis is put on coupled modes occurring in magnetic double layers, i.e. two ferromagnetic films, separated by a nonferromagnetic interlayer. The coupling can be via oscillating dipolar fields caused by the preccessing spins, or via the exchange interaction. It is shown, how the coupled modes can be used, to explore such interactions. These investigations have led to the discovery of the interlayer exchange interaction.

Light scattering from spin waves in thin films and layered magnetic structures

We have studied exchange coupling between ferromagnetic films across nonmagnetic intermediate layers by means of light scattering from spin waves and microwave absorption. The ferromagnetic films were Ni0.8Fe0.2 (permalloy) and Fe and we chose Au, Ag, Cu, V, Cr, Pd, Ge, Si, Mn, and Bi as nonmagnetic interlayer materials. As expected the effective interlayer exchange decreases when the interlayer thickness d0 increases. Minimum thickness d0 where the ferromagnetic films are exchange decoupled range between 10 and 40 A. We compare these results with the concentration dependence of the magnetic ordering temperature in alloys of Fe and Ni with other elements, taking this as a measure for the strength of the exchange. There is a good correspondence which indicates that the coupling effects in the layered structures and the alloys have the same origin which is presumably by RKKY interaction.

P. Swiatek

Papers

Exchange coupling of ferromagnetic films across nonmagnetic interlayers