Figures

Figure 1. RHEED pictures of Fe/Ag/Co_xFe_1-x/Ag sandwiches at various stages of growth. a) <110> and <100> azimuthal RHEED views of bcc Fe(001) grown on ZnSe. b) <100> and <110> azimuthal RHEED views of a representative fcc Ag(001) spacer layer grown on bcc Fe(001). c) <110> and <100> azimuthal RHEED views of the bcc Co47Fe53(001) grown on Ag (001). RHEED patterns from x = 0.71 and x = 0.30 Co_xFe_1-x alloy films grown on Ag(001) are similar. d) <110> and <100> azimuthal RHEED view of pure Co grown on Ag(001). While the complicated RHEED pattern does not exactly correspond to that of bcc Fe, the principal diffraction features are coincident. Ferromagnetic resonance and magnetization measurements on the Co film show that it has a cubic anisotropy.[Photos take too much storage and too long to load; email me and ask for a hardcopy if you want to see them!]

Figure 2: a) H||(100) magnetization curve for a Fe81Å/Ag84Å/Co111Å sandwich. The low-field reversal is due to the Fe film, and the high-field reversal is due to Co. Ferromagnetic resonance shows no interlayer coupling.

b) Magnetoresistance loop for the same sample in the same orientation. The resistance is enhanced in the field region Hc, Fe < |H| < Hc, Co where the moments of the two ferromagnetic layers are antiparallel. The solid line indicates the sweep from positive to negative fields, whereas the dashed line indicates the sweep from negative to positive fields.

Figure 3: a) H||(100) magnetization curve for a Fe76Å/Ag65Å/(Fe29Co71)84Å/Ag33Å sandwich. This orientation is the easy axis for the Fe film, which reverses in the square portion of the loop, but is the hard axis for the alloy film, which contributes the linear magnetization tail at higher fields.

b) Detail showing low-field behavior. Circles indicate the field region where the moments are 135 degrees apart, as sketched in the diagrams. The nearly horizontal parts of the loop correspond to the two moments being oriented 45 degrees apart for both directions of sweep (marked as in Fig. 2b)).

c) H||(100) magnetoresistance curve for the same sandwich. The resistance is maximum in the field range where the angle between the Fe and alloy moments is 135 degrees (as illustrated in Fig. 3b). Dashed and solid lines are as in part b).
Figure 4: a) H||(110) (hard axis) loop for a Fe131Å/Ag55Å/Fe124Å/Ag28Å sandwich. Both Fe films have a (100) easy axis.

b) H perpendicular to I||(110) magnetoresistance of the same sandwich. Note the second peak in the magnetoresistance, which does not correlate with any discontinuity in the magnetization curve. This second peak is believed to correspond to the reversal of a component of the magnetization which is orthogonal to the applied field, and thus not directly observable by the magnetometer. Dashed and solid lines are as in Fig. 2.

Figure 5: MRpeak and anisotropic magnetoresistance (AMR) vs. alloy composition. The AMR is approximately linear with alloy composition. The dashed curve through the MR data is a guide to the eye only.

Figure 6: a) Giant magnetoresistance coefficientG and field-induced change in resistance Dr and b) magnetic moment data vs. alloy composition. The magnetic moment data is from Ref. 30. G is the angle-independent, intrinsic measure of magnetoresistance magnitude in a ferromagnet/paramagnet/ferromagnet sandwich. The dashed lines in both these plots are guides to the eye, not fits.