Electric transport in Fe/ZnSe/Fe heterostructures (original) (raw)
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Perpendicular electric transport in Fe/X/Fe model heterostructures
Journal of Applied Physics, 2002
Based on the Kubo-Greenwood equation as formulated for layered systems, an approach is discussed that allows us to separate the resistance of the current leads from that of the region whose resistance we wish to calculate for current perpendicular to the plane of the layers. By applying this approach to Fe/Ge/Fe model structures related to the parent lattice of bcc Fe we find that at least nine layers of the magnetic electrodes should be considered as being part of the calculation in order to perform such a separation. With different structures in the Ge spacer, we find that the concentration of vacancies plays a crucial role for the existence of a sizeable magnetoresistance ͑MR͒, while the actual structure in the spacer seems to be of less importance. Depending on the type of structure and the number of spacer layers ͑in a typical regime of 6 -21 layers͒ the MR for ordered structure varies between 35% and 45%. Vacancy concentrations of more than 10%, however, wipe out the MR completely. Interdiffusion at the Fe/Ge interfaces produces very similar effects.
Magnetoresistance in Fe/ZnSe/Fe planar junctions
Journal of Magnetism and Magnetic Materials, 2001
We report on the magnetoresistance measurements in Fe/ZnSe/Fe planar junctions. Fe/ZnSe/Fe structures were successfully grown by molecular beam epitaxy and subsequently patterned using optical lithography. At low temperature, the tunneling of electrons from one Fe layer to the other through ZnSe gives arise a small tunneling magnetoresistance ((0.1%) associated with the relative alignment of magnetic moments in the two Fe layers. Also, a large positive magnetoresistance ('100%) with an almost quadratic "eld dependence was observed for "eld as high as 80 kOe.
Perpendicular transport in Fe/Ge model heterostructures
Physical Review B, 2001
Based on the Kubo-Greenwood equation as formulated for layered systems, an approach is discussed that allows us to separate the resistance of the current leads from that of the region whose resistance we wish to calculate for current perpendicular to the plane of the layers. By applying this approach to Fe/Ge/Fe model structures related to the parent lattice of bcc Fe we find that at least nine layers of the magnetic electrodes should be considered as being part of the calculation in order to perform such a separation. With different structures in the Ge spacer, we find that the concentration of vacancies plays a crucial role for the existence of a sizeable magnetoresistance ͑MR͒, while the actual structure in the spacer seems to be of less importance. Depending on the type of structure and the number of spacer layers ͑in a typical regime of 6-21 layers͒ the MR for ordered structure varies between 35% and 45%. Vacancy concentrations of more than 10%, however, wipe out the MR completely. Interdiffusion at the Fe/Ge interfaces produces very similar effects.
Fe/ZnSe/Fe junctions: Interplay between interface structure and tunneling magnetoresistance
Physica B: Condensed Matter, 2009
We investigate the electronic structure of Fe/ZnSe/Fe magnetic tunnel junctions for which interdiffusion and reconstruction at the interfaces are considered. Taking into account the ab initio potential profile throughout the different layers of the structure, we discuss about its implications on the tunnel conductance. Our results show that interface reconstruction drives changes in the electronic structure which, in turn, produce an increase of the kinetic energy of the conduction electrons, independently of their spin orientation. We suggest that this reconstruction underlies the low tunnel magnetoresistance (TMR), as it is observed in transport measurements when compared with the theoretical value estimated for sharp interfaces.
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%.
Magnetic moments and anisotropies in ultrathin epitaxial Fe films on ZnSe(001)
Journal of Applied Physics, 2000
The morphology, atomic magnetic moments, and in-plane magnetic anisotropies of ultrathin bcc Fe͑001͒ films deposited by molecular beam epitaxy on ZnSe epilayers grown on GaAs͑001͒ single crystal are reported. The growth mode and structure have been determined in situ by means of reflection high energy electron diffraction and Auger electron spectroscopy. The magnetic properties were characterized ex situ by an alternating gradient magnetometer, superconducting quantum interference device ͑SQUID͒ magnetometry, and conversion electron Mössbauer spectroscopy ͑CEMS͒. The Fe growth is epitaxial and occurs by three dimensional nucleation at the beginning. The coalescence of the islands is observed around 7 monolayers ͑ML͒. In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe monolayers. Determination of the in-plane anisotropy constants as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy, which leads to a continuous evolution from a pure uniaxial anisotropy with easy axis along ͓110͔ direction for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML.
Magnetic properties of Fe/ZnSe/Fe trilayers
Physica B: Condensed Matter, 2002
The magnetic properties of Fe/Zn/Fe trilayers have been studied by ferromagnetic resonance and magnetization measurements. These measurements have been used to investigate the magnetic anisotropy of the iron layers and the magnetic coupling across the semiconductor spacer. The angular dependence of the resonance spectra has been measured in-plane and out-of-plane in order to deduce magnetic anisotropy constants of the samples. Experimental data were fitted by using an energy-density expression that includes bulk cubic anisotropy, growth-induced uniaxial inplane anisotropy and perpendicular-surface anisotropy terms. A small ferromagnetic coupling is observed in the trilayers with spacer thickness up to 50 ( A: r
Materials
In ferromagnetic semiconductors, the coupling of magnetic ordering with semiconductor character accelerates the quantum computing. The structural stability, Curie temperature (Tc), spin polarization, half magnetic ferromagnetism and transport properties of ZnX2Se4 (X = Ti, V, Cr) chalcogenides for spintronic and thermoelectric applications are studied here by density functional theory (DFT). The highest value of Tc is perceived for ZnCr2Se4. The band structures in both spin channels confirmed half metallic ferromagnetic behavior, which is approved by integer magnetic moments (2, 3, 4) μB of Ti, V and Cr based spinels. The HM behavior is further measured by computing crystal field energy ΔEcrystal, exchange energies Δx(d), Δx (pd) and exchange constants (Noα and Noβ). The thermoelectric properties are addressed in terms of electrical conductivity, thermal conductivity, Seebeck coefficient and power factor in within a temperature range 0–400 K. The positive Seebeck coefficient shows p...
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.
Journal of Applied Physics, 2013
Structural, electronic, and magnetic properties of Fe/CaS (001) interfaces and Fe/CaS/Fe (001) heterostructures have been studied by means of a self-consistent Green's function technique for surface and interfaces implemented within the tight-binding linear muffin-tin orbital formalism. Spin dependent transport properties of the Fe/CaS/Fe (001) tunnel junctions with thin and intermediate barriers, in the current-perpendicular-to-plane geometry, have been determined by means of Kubo-Landauer approach implemented within the tight-binding linear muffin-tin orbital formalism. A small charge rearrangement is evidenced at the Fe/CaS (001) interfaces. The iron interfacial magnetic moments are enhanced over the bulk value. A small exchange coupling with the sign depending on the Fe/CaS (001) interface geometric structure and the strength decaying exponentially with the barrier is evidenced. Interfacial charge transfer, interface iron magnetic moments, and tunneling currents are sensitive to the interfacial structure. Interface resonant states have a decisive role in the tunneling process and the main contribution to the current in the ferromagnetic state of the junction is given by the minority-spin electrons. V C 2013 American Institute of Physics.