Enhancement of perpendicular and parallel giant magnetoresistance with the number of bilayers in Fe/Cr superlattices

Abstract

We have correlated a detailed quantitative structural analysis by x-ray diffraction, transmission electron microscopy, and high spatial resolution electron energy-loss spectroscopy imaging, with the magnetization and anisotropic magnetotransport properties in sputtered Fe/Cr superlattices. To accomplish this, we developed a technique for magnetotransport measurements in metallic superlattices with the current perpendicular to the plane of the layers ͑CPP͒. Using microfabrication techniques, we have fabricated microstructured Fe/Cr pillars embedded in SiO 2 and interconnected with Nb electrodes. Because of the uniform current distribution in the Nb electrodes and the minimization of the superlattice-electrode contact resistance, the method allows a simple and independent measurement of the superlattice resistance and giant magnetoresistance ͑GMR͒. Structural and magnetic characterization of ͓Fe ͑3 nm͒/Cr ͑1.2 nm͔͒ N superlattices ͑where N is the number of repetitions͒ indicate that the roughness is correlated and increases cumulatively through the superlattice stack with no significant change in the antiferromagnetic coupling. Both the current in-plane and CPP GMR increase with N as the roughness increases.

Effects of epitaxial strain on the growth mechanism inYBa2Cu3O

“…Combining both techniques it is possible to accurately quantify the interfacial roughness in both the growth and lateral directions. 9 We have found a correlation between the release of epitaxial strain in YBCO layers, when a certain critical thickness is attained, and the appearance of roughness in the superlattices, which increases with layer thickness and confirms a 3D-like growth in relaxed samples. The films for this study were ͓YBCO n /PBCO 5 ͔ 1000 Å superlattices with nominal values for YBCO layer thickness n comprised between 1 and 12 unit cells up to a total thickness of 1000 Å.…”

“…first bilayer, ␣ϭ0.51 an exponent which accounts for the cumulative roughness evolution, and N the bilayer index. 9,16 No fluctuations were found in the height distribution of each bilayer in the ͓YBCO 2 /PBCO 5 ͔ 1000 Å superlattice within the lateral size of the images. Figure 4 shows the XRD spectra of a YBCO 1 /PBCO 5 sample ͑bottom͒ and a YBCO 8 /PBCO 5 superlattice ͑top͒, displaced vertically for clarity.…”

“…This method has been proposed recently and satisfactorily applied to analyze the interface roughness in Fe/Cr superlattices. 9 Histogram plots of the modulation length distributions are shown in Figs. 2͑a͒ and 2͑b͒, respectively, for the ͓YBCO 2 /PBCO 5 ͔ 1000 Å and ͓YBCO 8 /PBCO 5 ͔ 1000 Å superlattices of Fig.…”

Ab initio study of CPP transport in Fe/Cr/Fe trilayers: influence of transition metal impurities

“…The discovery of the giant magnetoresistance (GMR) in Fe/Cr multilayers by Baibich el al. [ I ] and the observation of the oscillating interlayer exchange coupling (IEC) two years earlier by Grtinberg and coworkers [2] was the starting point of many intense studies of the electronic transport in these systems [3][4][5][6]. Recently, some effort has been devoted to examine the IEC in Fe/Cr/Fe trilayers with Mn impurities in the Cr spacer [7].…”

Influence of surface roughness and deposition order on exchange bias in bilayer structures NiFe/IrMn

“…A major portion of publications shows that exchange bias shift decreases when roughness increases [1][2][3][4], though no significant correlations between H EB and roughness was found in some of the works [5,6]. An opposite effect, that is H EB increasing when roughness increased, was also demonstrated in other investigations, [1,3,7], for instance, in monocrystalline silicone AF (with compensated and uncompensated surface), covered with an F-layer.…”