Enhanced giant magneto-resistance in spin-valves sandwiched between insulating NiO

We have investigated the giant magnetoresistance of artificial structures containing metallic Co/Cu/Co and Ni80Fe20/Cu/Ni80Fe20 spin-valves confined within insulating antiferromagnetic NiO layers. The observed enhanced magnetoresistance as compared to conventional all-metal spin-valves is interpreted with a semiclassical approach in which specular reflections at the metal/insulator barrier are included

Short period oscillation of the interlayer exchange coupling in the ferromagnetic regime in Co/Cu/Co(100)

\u3cp\u3eA unique sample was prepared on a Cu(100) single crystal, consisting of three Co layers separated by two Cu layers in the form of wedges oriented perpendicular to each other: Cu(100)/80 Å Co/Cu wedge A/30 Å Co/Cu wedge B/30 Å Co/7 Å Cu/30 Å Au. Position-sensitive magneto-optical Kerr effect measurements along Cu wedge B, at a fixed position on Cu wedge A corresponding to maximum antiferromagnetic (AF) coupling, enabled us to investigate not only the AF but also the ferromagnetic (F) coupling between the two 30 Å Co layers as a function of the Cu thickness. The measurements confirmed both long and short period coupling oscillations in the AF regime, and revealed the predicted extension of the short period through the F regime.\u3c/p\u3

Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co

A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness has been observed. The Co thickness dependence displays two clear peaks consistent with the recently predicted oscillation period of 6.2 Å Co. Apart from the two peaks also several small peaks are visible on a scale of about 1 monolayer Co. Free-electron calculations indicate that these rapid variations in strength may result from slight differences between the slopes and starting points of the two Co wedges that were involved in the experiment. Journal of Applied Physics is copyrighted by The American Institute of Physics

Spatial resolution of domain copying in a magnetic domain expansion readout disk

In a magnetic amplifying magnetooptical system (MAMMOS) disk, the copying process of a magnetic domain from the recording layer into the readout layer is investigated by using a laser spot diameter of 0.66 µm. Interference between neighboring bits occurs when the spatial resolution of the copy process is larger than half the domain size. It is observed that a reduction of the readout power from 2.3 to 2.0 mW corresponds to a decrease of the copy window from 0.5 to 0.06 µm. As a result, at 2.0 mW packed magnetic domains with a width of only 0.11 µm have been resolved without interference by using domain expansio

Orientational dependence of the oscillatory exchange interaction in Co/Cu/Co

\u3cp\u3eA strong oscillatory exchange coupling has been discovered in epitaxial (111) and (110) Co/Cu/Co sandwiches with wedge-shaped Cu layers, deposited by molecular-beam epitaxy (MBE) on single-crystal substrates. This finding proves the intrinsic nature of the strong antiferromagnetic coupling in (111)-textured sputtered Co/Cu multilayers. Combined with recent results on (100) Co/Cu/Co MBE-grown samples, it becomes evident that the nature of the oscillations in Co/Cu/Co depends markedly on growth direction, agreeing with predictions invoking the topology of the Fermi surface of the interlayer Cu.\u3c/p\u3

Magnetic and transport behavior of Af-coupled layers with a limited number of repetitions

\u3cp\u3eWe investigated the magnetization behavior of [(Co/Pd)4-Ru]x samples with perpendicular anisotropy and a limited number of repetitions (x=1,..22). In these systems the Co/Pd multilayers behave as single magnetic entices. A detailed analysis and comparison of the magnetization curves observed by MOKE and VSM permits us to observe the magnetization reversal and hysteresis of the individual layers and to determine the antiferromagnetic coupling J between each pair of layers. A gradual increase in J is observed in all samples when going from the bottom layer to the top layer. Magnetoresistance curves show the same sharp transitions as the magnetization curves. A clear distinction can be made between an outer layer and an inner layer. These results will be compared with model calculations.\u3c/p\u3

Oscillatory interlayer exchange coupling with the Cu cap layer thickness in Co/Cu/Co/Cu(100)

\u3cp\u3eAn oscillatory dependence of the strength of the antiferromagnetic exchange coupling on the cap layer thickness has been observed in an epitaxial Co/Cu/Co/Cu(100) sample with a wedge-shaped Cu interlayer and cap layer. The result is consistent with a single long oscillation period stemming from the extremal spanning vector of the Cu (cap layer) Fermi surface along the X line. The absence of a short period oscillation is understood from the confinement of the corresponding electron states to the spacer. A quantitative comparison with Bruno's model is made.\u3c/p\u3

Orientational dependence of oscillatory exchange coupling

\u3cp\u3eThe role of the interlayer Fermi surface in driving oscillatory exchange coupling of ferromagnetic layers has been critically tested in a series of MBE-grown coherent epitaxial sandwiches prepared on single-crystal substrates. The wedge-shaped Cu (or Cu-based) interlayers have been modified in a number of different ways, achieving orientational, compositional and structural alteration of the Cu Fermi surface. Observed phenomena include multiperiodic coupling oscillations in both the ferromagnetically and antiferromagnetically coupled regions.\u3c/p\u3

Phase shifts in the oscillatory interlayer exchange coupling across Cu layers

The dependence of the phase of the oscillatory exchange coupling between ferromagnetic (FM) layers across fcc Cu on the composition of the ferromagnetic layer has been studied in several epitaxial samples. In the case of (001) systems, phases remain constant for the long period oscillation, but for the short period oscillation they vary monotonically with the d-electron occupation number of the FM layers, at a rate of about 1.5 Å/electron. In the case of (110) systems the variation is nonmonotonic. A framework is presented with which the above observations can be understood