P Belien

Giant magnetoresistance in Fe/Cr superlattices with very thin Fe layers

Carefully tailored Fe/Cr epitaxial superlattices with extremely thin Fe layers have been grown on MgO(100) by molecular beam epitaxy. The low‐angle x‐ray spectra reveal the presence of sharp interfaces down to an Fe layer thickness of a few monolayers. An [Fe(4.5 A)/Cr(12 A)]50 superlattice shows a 220% magnetoresistance at 1.5 K, and a saturation field of 110 kOe. A further decrease of the Fe layer thickness produces a drastic decrease in the magnetoresistance.

Interplay between interface properties and giant magnetoresistance in epitaxial Fe/Cr superlattices

Epitaxial Fe/Cr superlattices with negligible intralayer scattering have been grown on MgO(100) using MBE. The careful structural analysis of such superlattices prepared under different conditions reveals the details of the interfacial origin of the giant magnetoresistance (GMR). We find the highest GMR in samples with minimum intermixing but an enhanced density of steps at the interfaces. Such Fe/Cr superlattices display GMR amplitudes up to 220%.

On the Fe thickness dependence of the giant magnetoresistance in epitaxial Fe/Cr superlattices

Abstract We analysed the transport properties of Fe/Cr(100) superlattices as a function of the Fe thickness. We find two magnetic inactive atomic layers and interpret the magnetoresistance with the quasi-classical formalism based on the Boltzmann kinetic equation.

The superconducting proximity effect in Nb/Fe multilayers

Abstract We prepared Nb/Fe multilayers with varying Nb or Fe thickness by means of MBE. The x-ray diffraction patterns show good layering quality. Critical field measurements as a function of temperature and angle demonstrate that very thin Fe layers (≈ 12 A) decouple the Nb layers completely thus leading to 2D behaviour of the multilayers. The dependence of T c as a function of Nb thickness and the critical fields are well described by the theoretical model derived for the proximity effect in superconductor/ferromagnet multilayers.

Influence of different kinds of interface roughness on the giant magnetoresistance in Fe/Cr superlattices

Abstract We present a detailed study of the influence of the interface properties on the amplitude of the GMR in Fe/Cr superlattices, including changes of the coupling, a synchrotron X-ray diffraction analysis and a theoretical interpretation within the quasi-classical formalism. With increasing amplitude of the interface roughness we observe a reduction of the GMR.

Electric transport properties of epitaxial Fe and Cr films with very low intralayer scattering

The low-temperature transport properties of epitaxial Fe and Cr films grown on MgO(1 0 0) substrates by molecular beam epitaxy are characterised by extremely low intralayer resistivities, indicating a very small concentration of defects. This makes such films particularly suitable for studies of the influence of the interface scattering on the transport properties of Fe/Cr superlattices.

Analysis of the transport properties of epitaxial Fe and Cr films

Molecular beam epitaxy of Fe and Cr on single crystalline MgO(001) substrates produces films with very small defect concentrations. Accordingly, their low temperature transport properties are characterized by extremely low bulk resistivities. The temperature dependence of the resistivity of the Cr films shows anomalies due to magnetic ordering effects around the Neel temperature . We find values of K which is close to the bulk value. The anomalous Hall effect of the Fe films shows typical ferromagnetic behaviour. The spontaneous Hall coefficient is proportional to the square of the resistivity indicative of side jump scattering. Fe/Cr superlattices grown under similar conditions are particularly suitable to study the influence of interface scattering on the giant magnetoresistance amplitude.

Magnetoresistance and magnetization oscillations in Fe/Cr/Fe trilayers

The 2‐ML (monolayer) oscillation period has been observed in the magnetization as well as in the magnetoresistance of Fe/Cr/Fe trilayers. Kerr effect measurements were performed in order to verify the periodicity and determine the kind of the coupling between the Fe layers. The magnetoresistance loops show characteristic steps at magnetic field values at which the size of the magnetization changes.

GIANT MAGNETORESISTANCE IN FE/CR SUPERLATTICES WITH AND WITHOUT BULK SCATTERING

Abstract Giant magnetoresistance (GMR) observed in magnetic multilayers is due to spin-dependent electron scattering at interfaces and bulk defects. In order to separate these two possible contributions we studied Fe/Cr superlattices with and without bulk defects (respectively polycrystalline and epitaxial samples). The interface roughness was quantitatively analysed using X-ray diffraction and conversion electron Mosbauer spectroscopy. The magnitude of the GMR effect depends on both the vertical roughness amplitude η and the lateral correlation length ξ x and increases with increasing η / ξ x .

Structural analysis of Fe/Cr superlattices and their components

Structural analysis of metallic superlattices is essential for understanding their interesting transport properties like the giant magnetoresistance (GMR) effect. We present a detailed analysis of the superlattice which shows a record GMR value. The analysis is done by simulating its x-ray diffraction spectrum measured with a synchrotron x-ray source. The ingredients for this simulation are obtained from simulations of x-ray diffraction spectra of single Fe and Cr films. This way we reduce the number of free parameters resulting in reliable values for the interfaces roughness. We also show that x-ray diffraction spectra of systems with low contrast in electron density can be quantitatively analysed.