Ab Initio Study of Electric Transport and Interlayer Exchange Coupling in Fe-Si-Fe Systems (original) (raw)
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Interlayer exchange coupling and perpendicular electric transport in Fe/Si/Fe trilayers
Physical Review B, 2002
The interlayer exchange coupling and the perpendicular magnetoresistance of Fe/Si/Fe systems have been investigated within the fully relativistic screened Korringa-Kohn-Rostoker method and the Kubo-Greenwood equation considering interdiffusion effects, i.e., inhomogeneous Fe-Si alloy formation at the interfaces. It is shown that the experimentally observed strong antiferromagnetic interlayer exchange coupling is caused by the formation of Fe-Si alloys at the interface. Furthermore, our calculations give evidence that the small magnetoresistance, which has been observed experimentally in Fe/Si/Fe trilayers has a similar origin. The results presented here give no evidence for a direct connection between the magnetoresistance and interlayer exchange coupling in Fe/Si/Fe systems.
Magnetic properties, interlayer exchange coupling and electric transport in Fe/Cr/Fe trilayers
2002
Based on the fully relativistic spin-polarized screened Korringa±Kohn± Rostoker method and the Kubo±Greenwood equation as formulated for layered systems the interlayer exchange coupling (IEC) as well as the magnetoresistance (MR) for the current in-plane (CIP) geometry is calculated for Fe/Cr/ Fe trilayer systems. For the IEC not only short periods of 2 monolayers (ML) but also long periods of about 18 ML are found. For large Cr thicknesses the magnetic moments oscillate with a period of 8±9 ML for even numbers of Cr layers and 18 for odd. The calculated CIP MR and corresponding resistivities are in the range of available experimental data. It is found that the peaks in the CIP MR have little in common with the oscillation periods characterizing the IEC.
Theory of electric transport through Fe/V/Fe trilayers including the effect of impurities
physica status solidi (b), 2005
PACS 75.47.De, 75.70.Cn The influence of Al and Si impurity layers on the giant magnetoresistance (GMR) and the magnetic properties of Fe/V/Fe(110) trilayers is investigated. The calculations are performed by employing the spinpolarized Kubo-Greenwood approach and the screened Korringa-Kohn -Rostoker method for layered systems. All calculations are carried out with a fully-relativistic version. Therefore, we are able to consider also anisotropic magnetoresistance effects, which are common in Fe/V systems. We find that the AMR always makes a tiny contribution to the resistivity in alike multilayers so that the magnetoresistance is entirely due to the GMR. A reduction of the GMR due to the Al and Si impurities is observed for current in-plane (CIP) and perpendicular (CPP) geometry. However, in the case of CIP geometry the influence of the impurities decreases with increasing V layer thickness, whereas in the CPP case the difference alternates between 0 and 7%.
Exchange coupling of ferromagnetic films across metallic and semiconducting interlayers
Journal of Physics-condensed Matter, 2003
Recent results obtained in our laboratories on interlayer exchange coupling of Fe films across interlayers of iron silicides, Fe 1−x Si x with x = 0.5-1, are reviewed. Samples are prepared by molecular beam epitaxy and characterized by means of low-energy electron diffraction and cross-sectional transmission electron microscopy. Coupling across interlayers of iron silicide with x ≈ 0.5 is found to be oscillatory with a strength of the order of 1 mJ m −2 , and across well ordered Si interlayers (nominally x = 1) the coupling is exponentially decaying. In the latter case the maximum coupling turns out to be surprisingly strong (>6 mJ m −2 ), in particular considering the fact that the electrical resistivity is found to be large. Current-voltage curves for currents across the interlayers are characteristic of electron tunnelling. Soft-x-ray emission and near-edge x-ray absorption spectroscopy further support a semiconducting nature for the nominally pure Si interlayers.
Ab initio study of CPP transport in Fe/Cr/Fe trilayers: influence of transition metal impurities
MRS Proceedings, 2002
The transport properties of Fe(001)/Cr/Fe(001) trilayers are discussed with respect to the influence of transition metal impurities in form of layers. We are able to show that the periodicity of the giant magnetoresistance is directly influenced by the interlayer exchange coupling (IEC). Furthermore, it is observed that the behavior of the IEC strongly depends on whether an impurity overlayer of Mn or V is used. It turns out that the size of the GMR is only little effected by 3d-transition metal impurities, which is in agreement with the experimental findings. The electronic and magnetic properties of the trilayers have been investigated within the fully relativistic, spin-polarized SKKR method and the LDA. The transport properties of the Fe/Cr/Fe systems have been derived from the fully relativistic spin-polarized Kubo-Greenwood equation.
Very strong interlayer exchange coupling in epitaxial Fe/Fe 1− x Si x /Fe trilayers ( x=0.4–1.0
Journal of Magnetism and Magnetic Materials, 2002
Fe/Fe 1Àx Si x /Fe (x=0.4-1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear (J 1 ) and biquadratic (J 2 ) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J ¼ J 1 þ J 2 increases dramatically with increasing x and reaches values in excess of 6 mJ/m 2 . r
Magnetism and magnetotransport in Fe/V/X/Fe (X= Al,Si) heterostructures
2004
We investigate the electrical transport and the magnetic properties of Fe/V/Fe(110) trilayers depending on the thickness of the V layer and on the existence of impurity layers (Al, Si) on top of the V spacer. From experiments it is known that the induced magnetic moments of V rapidly decrease with increasing number of V layers. Here, we examine in how far the magnetic behavior of V influences the conductivity and resistivity of the trilayers. For thin V layers we observe a rapid increase of the conductivity, which seems to be related to a small jump in the total magnetic moment of V. Additional calculations are performed by replacing V through Fe_(3-x)V_xAl. The Heusler alloy is interesting for transport purposes because of its tunable magnetic properties. The screened Korringa-Kohn-Rostoker method is used to investigate the electronic and magnetic properties of the trilayers. In order to determine the conductivity and the magnetoresistance we make use of the Kubo-Greenwood formula. This work is funded by the Deutsche Forschungsgemeinschaft through the SFB 491.
Dependence of the interlayer exchange coupling on the constitution of the magnetic layers
Journal of Applied Physics, 1996
We describe the consequences on the interlayer exchange coupling by the addition of a small amount of Ag impurities within the Co layers of high crystalline quality Co/Cu/Co͑Ag͒ and Cu/ Ru/Co͑Ag͒ trilayers, while maintaining the integrity of the spacer layers. We discuss the consequent changes in the amplitude, period, and phase of the coupling in terms of the modification of interfacial spin-dependent potentials.
Physical Review B, 2005
Spin dependent interfacial resistance ͑R I ͒ is crucial for achieving high spin injection efficiency from a ferromagnetic ͑FM͒ metal into a semiconductor ͑SC͒. We present a self-consistent model of spin transport across interfacial resistances at the FM-SC junctions of a FM-SC-FM trilayer structure. The SC layer consists of a highly doped n ++ AlGaAsu GaAs 2DEG while the interfacial resistance at the FM-SC junction is modeled as delta potential ͑␦͒ barriers. The self-consistent scheme consists of a ballistic model of spindependent transmission across the ␦ barriers to evaluate R I , and a drift-diffusion model to obtain the spin-split ⌬ in the electrochemical potentials. The R I values of the two junctions were found to be asymmetric despite the symmetry of the trilayer structure. This asymmetry arises from the finite biasing voltage which causes a difference in electrochemical potentials and spin accumulation at the two interfaces. The effect of R I on the spin-injection efficiency and magnetoresistance is studied over a range of ␦-barrier heights. Significant spininjection efficiency ͑50% ͒ requires high ␦-barrier heights approaching 1 eV. Even higher barrier heights are required to obtain equivalent magnetoresistive effect.