Perpendicular transport in Fe/Ge model 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.
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%.
Theory of tunneling magnetoresistance for epitaxial systems
IEEE Transactions on Magnetics, 2005
The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes through an epitaxial crystalline barrier can be calculated from first principles. These calculations show that the wave function symmetry can be exploited to achieve very high tunneling magnetoresistance. For the Fe(100) MgO(100) Fe(100) system, the calculated conductance is much higher and its decrease with MgO thickness is much slower than has been estimated using a simple free electron-barrier model.
Magnetoresistance measurements on Fe/Si and Fe/Ge multilayer thin films
Journal of Magnetism and Magnetic Materials, 2005
The magnetoresistance and magnetization of multilayer Fe/Si and Fe/Ge films on GaAs were measured simultaneously as a function of magnetic field along the in-plane ½1 1 0 and ½11 0 directions of the Fe. The field induced changes in the magnetoresistance and magnetization for each film are discussed in terms of the exchange coupling between the iron layers, and the thickness of the semiconductor spacer layer. The data show that there is exchange coupling across Ge spacer layers for layer thickness less than 1.2 nm.
Current-perpendicular-to-plane magnetoresistance in epitaxial Co2MnSi∕Cr∕Co2MnSi trilayers
Applied Physics Letters, 2006
Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of the multilayer thin film using a full-Heusler Co2MnSi (CMS) phase as ferromagnetic electrodes has been investigated. A multilayer of Cr buffer (10nm)∕CMS (50nm)∕Cr spacer (3nm)∕CMS (10nm)∕Cr cap (3nm) was grown on a MgO(100) substrate. The 50nm thick CMS layer which was deposited on the Cr buffer at 573K was epitaxially grown and had an L21 structure. The resistance change-area product (ΔRA) at room temperature was 19mΩμm2, which is one order of magnitude larger than those in previously reported trilayer systems, resulting in the MR ratio of 2.4%. A possible origin of the enhanced ΔRA is considered to be the large spin polarization in a high-quality L21 CMS film.
Current-perpendicular and current-parallel giant magnetoresistances in Co/Ag multilayers
Physical Review B, 1995
We report results of measurements of the perpendicular [current perpendicular to the layer planes (CPP)] and parallel [current in the layer planes (CIP)] magnetoresistances (MRs) of Co/Ag multilayers having Co and Ag thicknesses tc, and tAs ranging from 1.5 to 60 nm. (1) We find the variations of the CPPand CIP-MRs with tAg and tc, to be qualitatively similar to each other, suggesting that the parameters determining both may also be similar. (2) In accord with predictions that CPP-MR)CIP-MR, we find their ratio m=CPP-MR/CIP-MR to range from about 3 to at least 6. (3) We analyze current perpendicular to the layer plane (CPP) specific resistances, Ar, , of Co/Ag multilayers having a wide range of Co and Ag thicknesses tc, and tAg in terms of a two-current, series resistor model based upon the assumption that the spin-diffusion lengths in the Co and Ag are much longer than t«and tAg, respectively. We show first that a six parameter fit gives rather good agreement with four data sets, with the three parameters that can be separately checked agreeing within experimental uncertainties with independent measurements of the same quantities. We then examine the ability of these fits to predict the behavior of additional sets of data. Here we find some agreements and some disagreements. Possible reasons for the disagreements are examined.
First Principles Modeling of Tunnel Magnetoresistance of Fe/MgO/Fe Trilayers
Physical Review Letters, 2006
We report ab initio calculations of nonequilibrium quantum transport properties of Fe=MgO=Fe trilayer structures. The zero bias tunnel magnetoresistance is found to be several thousand percent, and it is reduced to about 1000% when the Fe=MgO interface is oxidized. The tunnel magnetoresistance for devices without oxidization reduces monotonically to zero with a voltage scale of about 0.5-1 V, consistent with experimental observations. We present an understanding of the nonequilibrium transport by investigating microscopic details of the scattering states and the Bloch bands of the Fe leads.
Journal of Physics: Condensed Matter, 2007
The ab initio full-potential linearized augmented plane-wave method explicitly designed for the slab geometry was employed to elucidate the physical origin of the layer potentials for the trilayers nFe/3Cr/nFe(001), where n is the number of Fe monolayers. The thickness of the transition-metal ferromagnet has been ranged from n = 1 up to n = 8 while the spacer thickness was fixed to 3 monolayers. The calculated potentials were inserted in the Fuchs-Sondheimer formalism in order to calculate the giant magnetoresistance (GMR) ratio. The predicted GMR ratio was compared with the experiment and the oscillatory behavior of the GMR as a function of the ferromagnetic layer thickness was discussed in the context of the layer potentials. The reported results confirm that the interface monolayers play a dominant role in the intrinsic GMR.