R. Loloee

Perpendicular-current exchange-biased spin-valve evidence for a short spin-diffusion lenght in permalloy

Abstract We present the first measurements of giant magnetoresistance with current perpendicular to the layer planes (CPP-MR) of an exchange-biased spin-valve (EBSV) - a controllable spin-switch. Interpreted with the theory of Valet and Fert, data on EBSVs of permalloy (Py) with Cu yield an unexpectedly short spin-diffusion length in Py − l sf Py =5.5± nm. Such a short length has implications for the interpretation of Johnsons data on a Py/Au/Py spin-switch.

Spin-memory loss at 4.2 K in sputtered Pd and Pt and at Pd/Cu and Pt/Cu interfaces

We derive spin-diffusion lengths at 4.2 K in sputtered Pd and Pt of lsfPd=25−5+10 nm and lsfPt=14±6 nm, interface specific resistances of sputtered Pd/Cu and Pt/Cu of 2ARPd/Cu=0.9±0.1 fΩ m2 and 2ARPt/Cu=1.5±0.1 fΩ m2, and the amount of spin-memory loss at the Pd/Cu and Pt/Cu interfaces as δPd/Cu=0.24−0.03+0.06 and δPt/Cu=0.9±0.1. We compare our values with those from metals in similar rows of the Periodic Table, Nb for Pt and W for Pd.

Giant magnetoresistance with current perpendicular to the layer planes of Ag/Co and AgSn/Co multilayers (invited)

A two‐channel model of electronic conduction is shown to provide a satisfactory description of the magnetoresistances of Ag/Co and AgSn/Co multilayers with the current flowing perpendicular to the layer planes. A combination of data for as‐prepared samples at magnetic field H=0 (for which the magnetization M≊0), and for the same samples in the ferromagnetically ordered state, is used to extract ‘‘best’’ spin‐orientation‐dependent parameters of αCo=2.9(+0.5,−0.3) and αCo/Ag=12(+5,−2) from Ag/Co data and αCo=2.4(+1,−0.7) and αCo/AgSn=11(+7,−4) from AgSn/Co data.

Perpendicular-current transport in exchange-biased spin-valves

We have measured giant magnetoresistance (GMR) with current perpendicular to the layer planes (CPP-MR) in exchange-biased (EB) spin-valves-a controllable spin-switch. We will present CPP data on EB-spin valves of Permalloy (Py) and Cu, and explain how the data are analyzed. Interpreted with the theory of Valet and Fert, the data yield an unexpectedly short value for the length over which electrons lose spin-memory in Py, the spin-diffusion length, l/sub sf//sup Py/=5.5/spl plusmn/1 nm. We will show that the CPP parameters derived with the aid of single EB-spin-valves predict rather well the CPP-MRs of double EB spin-valves.

Magnetic multilayers: oscillatory interlayer exchange and giant magnetoresistance

Abstract We illustrate our presentation and discussion of the interlayer exchange and magnetoresistance properties in magnetic multilayers with experimental data on Fe/Cr, Co/Cu and Fe/Cu.

Controlled Normal and Inverse Current-Induced Magnetization Switching and Magnetoresistance in Magnetic Nanopillars

Combining pairs of ferromagnetic metals with different signs of scattering anisotropies, let us independently invert the magnetoresistance and the direction of current-driven switching in ferromagnetic/non-magnetic/ferromagnetic metal nanopillars. We show all four combinations of normal and inverse behaviors, at both room temperature and 4.2K. In all cases studied, the direction of switching is set by the net scattering anisotropy of the fixed (polarizing) ferromagnet. We provide simple arguments for what we see.

Epitaxial (100) iridium on A-plane sapphire: A system for wafer-scale diamond heteroepitaxy

Large-scale heteroepitaxial growth of diamond depends critically on the development of a suitable lattice-matched buffer layer and substrate system. Epitaxial (100) iridium films have been grown on terraced, vicinal a-plane (1120) α-Al2O3 (sapphire) by electron-beam evaporation. The epitaxial relationship, Ir(100)//Al2O3(1120) with Ir[011]//Al2O3[1100], was determined by x-ray diffraction and electron backscattering diffraction analysis. For a 300-nm thickness of Ir, a (200) rocking curve yielded a linewidth of 0.21°, and the film exhibited a macrostepped surface with low pinhole density. This Ir/sapphire system provides a basis for large-area growth of (100) heteroepitaxial diamond.

Giant magnetoresistance in Ag/Co and Cu/Co multilayers with very thin Co layers

Abstract The magnetoresistances (MR) of Ag/Co multilayers with fairly thick Co layers ( t Co ⩾1.5 nm) and relatively thin Ag layers ( t Ag ⩽3 nm) have been found to be much smaller than those for the sister Cu/Co series. Recently, however, Araki et al. reported very large MRs in Ag/Co multilayers with very thin Co layers ( t Co =0.6 nm) and sufficiently thin Ag layers. In this paper we provide additional data that expand and generally confirm Arakis observations, but lead us to propose that our Ag/Co samples with very thin layers are intermediate between multilayers and granular, with the smaller MRs for large t Co and the larger MR values for small t Co being due to a change in continuity of the Co layers. Comparative results are also presented for Cu/Co multilayers.

Inverse CPP-GMR in (A/Cu/Co/Cu) multilayers (A=NiCr, FeCr, FeV) and discussion of the spin asymmetry induced by impurities

We present CPP-GMR experiments on a series of multilayers of the type (A/Cu/Co/Cu)×N where A is a layer of NiCr, FeCr, or FeV alloys with concentrations of Cr or V between 2.5 and 30 at. %. The inverse GMR effects we observe can be accounted for by the opposite scattering spin asymmetries in Co (positive spin asymmetry) and A (negative spin asymmetry). As the spin asymmetry in A is positive for interface scattering and negative for bulk scattering, the inverse GMR is observed only for thicknesses greater than one at which interface and bulk scattering compensate. We determine the magnitude and sign of the spin asymmetry coefficients, and we notice the agreement with previous data on dilute alloys and with theoretical calculations.

Giant magnetoresistance of current-perpendicular exchange-biased spin-valves of Co/Cu

We present the first measurements of the specific resistance change, A/spl Delta/R, with increasing Co layer thickness, t/sub Co/, of current-perpendicular (CPP) exchange biased spin-valves (EBSVs) of Co and Cu. A/spl Delta/R grows about as predicted for a long spin diffusion length in Co until about t/sub Co/=20 nm, after which it grows more slowly than predicted. Possible reasons for this deviation from prediction are considered, including a short spin diffusion length in Co.