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We derive spin-diffusion lengths at 4.2 K in sputtered Pd and Pt of lsfPd=25−5+10 nm and lsfPt=14±6 nm, interface specific resistances of sputtered Pd/Cu and Pt/Cu of 2ARPd/Cu=0.9±0.1 fΩ m2 and 2ARPt/Cu=1.5±0.1 fΩ m2, and the amount of spin-memory loss at the Pd/Cu and Pt/Cu interfaces as δPd/Cu=0.24−0.03+0.06 and δPt/Cu=0.9±0.1. We compare our values with those from metals in similar rows of the Periodic Table, Nb for Pt and W for Pd.

Measurements at 4.2 K. of the magnetoresistance of Co/AgMn, Co/CuMn, Co/AgPt, and (:o/CuPi muitilayers with the current perpendicular to the layer planes (CPP-MR) show effects of reduced spin diA'usion lengths due to alloying of the nonmagnetic metal with impurities that produce spin-spin (Mn) or spin-orbit (Pt) scattering. Combining the data with u theory by Valet and Fert gives the spin diA'usion lengths in the alloys.

We present magnetoresistance measurements aimed at answering several open questions in the understanding of giant magnetoresistance ͑GMR͒. Our measurements are performed on (F1/N/F2/N) multilayers in which N is a nonmagnetic metal ͑Cu or Cr͒, and F1 and F2 are various ferromagnetic metals or alloys. In current perpendicular to the plane ͑CPP͒ measurements on (F1/Cu/Co/Cu) multilayers, where F1 is Fe, Co, or Ni doped with impurities, we observe an inversion of the GMR for V or Cr impurities; this demonstrates, first the importance of the extrinsic effects in GMR and secondly the possibility of obtaining negative as well as positive values of the bulk spin asymmetry coefficient ␤. A compensation thickness with zero GMR is found when the bulk and interface spin asymmetry have opposite signs in the same layer. We interpret the sign of ␤ in models of electronic structure. Measurements on other series of multilayers allow us to show that the interface spin asymmetry coefficient ␥ can also be positive ͑interfaces with Cu͒ or negative ͑interfaces with Cr͒. Finally, the comparison between CPP and CIP data obtained on the same samples sheds light on the different role of the interface intrinsic potential in the two geometries. ͓S0163-1829͑99͒09133-X͔

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The series resistor and Valet-Fert models widely used to describe the current-perpendicular-to-plane ͑CPP͒ magnetoresistances of ferromagnetic/nonmagnetic ͑F/N͒ metal multilayers were recently claimed to be valid only for mean-free paths shorter than layer thicknesses; otherwise the mean-free path was claimed to be an important length scale in the CPP magnetoresistance ͑MR͒. This claim was based on observations of differences in the CPP MR's, after the samples were taken to above their saturation magnetic fields, of two different kinds of multilayers involving Co and Cu: interleaved ͓Co(6)/Cu(20)/Co(1)/Cu(20)͔ N and separated ͓Co(6)/Cu(20)͔ N ͓Co(1)/Cu(20)͔ N , with N repeats and thicknesses in nm. The maximum CPP MR's of separated samples were only about half as large as those for interleaved ones. In two short papers, we provided experimental evidence that mean-free paths are not important length scales in the CPP MR by showing that the differences in CPP MR's upon which the above claim was made did not change when the mean-free paths in the N and F layers were reduced from well above to well below their layer thicknesses. We ascribed part of the behaviors of interest to finite spin-memory loss ͑spin flipping͒ in the F and N metals, and proposed that the rest might be due to spin flips at F/N interfaces. In the present paper we ͑a͒ present further experimental evidence against mean-free-path effects, ͑b͒ provide details of the calculations we use to analyze the data, and ͑c͒ use measurements of magnetization and polarized neutron reflectivity to show that the differences in CPP MR are not due to spurious differences in magnetic structure between interleaved and separated multilayers, but only to the differences in the relative magnetic alignment of adjacent layers. Additional evidence for this last point is our observation that the CPP MR's of separated samples in their as-prepared states are as large as those of the equivalent interleaved samples after they are taken to above their saturation fields. We show that similar differences between interleaved and separated data appear also in the current-in-plane ͑CIP͒ MR's and when the Cu is replaced by Ag.

Polarized neutron reflectivity and scanning electron microscopy with polarization analysis are combined to determine the magnetic structure of Co(6 nm)͞Cu(6 nm) multilayers. These data resolve a controversy regarding the low-field state of giant-magnetoresistive (GMR) multilayers with weak coupling. As-prepared samples show a strong antiparallel correlation of in-plane ferromagnetic Co domains across the Cu. At the coercive field, the Co domains are uncorrelated. This irreversible transition explains the decrease in magnetoresistance from the as-prepared to the coercive state. For both states, the Co moments reside in domains with in-plane sizes of ഠ0.5 1.5 mm.[S0031-9007(99)08797-9]