Influence of the FM/AFM interface morphology on the exchange coupling in epitaxial Co(001)/fct-Mn(001)

The Co thickness dependence of the exchange interaction between ferromagnetic (FM) fct-Co(001) and antiferromagnetic (AFM) fct-Mn(001) thin layers, epitaxially grown on Cu(001) single crystals, was studied. In the pseudomorphic Co growth regime, oscillations of the coercivity (HC) and the exchange bias (HE) with a Co at. monolayer period are obsd. These oscillations are explained by a biquadratic exchange interaction component at the FM/AFM interface which, in this thickness range, is modulated by the layer-by-layer growth mode of Co on Cu(001). [on SciFinder (R)

Electric-field gradients in thin face-centered-tetragonal Co films observed by nuclear magnetic resonance

Thin tetragonally strained fcc-Co films grown epitaxially on Cu(001) single crystals have been investigated by 59Co nuclear magnetic resonance (NMR). The ultrahigh structural quality and the homogeneity of the strain result in the direct NMR observation of electric-field gradients, which is unique in thin films. The structural quality and the homogeneity and size of the strain are analyzed by means of the very small NMR linewidths, the hyperfine field anisotropies, and the uniform electric-field gradients. A quantitative agreement with the observed strain is found. The strain, and thus the tetragonal distortion, in the films is found to be surprisingly stable, showing less than 10% strain relief for 80 ML Co films

Monolayer resolved oscillating hyperfine fields in epitaxial face-centered-tetragonal Co(001) films

Ultrahigh-quality thin fct-Co films grown on Cu(001) were studied by 59Co NMR. The influence of the spin-dependent electron scattering at the interfaces is obsd. for at least four Co at. layers from the interface with monolayer resoln. An oscillatory effect on the Co hyperfine field with a period of several monolayers is measured, corresponding to the oscillating conduction electron polarization. The observation is exclusively possible in this system due to its very narrow resonance lines, corresponding to a virtually perfect Co structure. [on SciFinder (R)

Formation of nonmagnetic c-Fe_{1-x}Si in antiferromagnetically coupled epitaxial Fe/Si/Fe

Low-energy electron diffraction, Auger electron spectroscopy, and conversion electron Mössbauer spectroscopy have been applied to study antiferromagnetically exchange-coupled epitaxial Fe/Si/Fe(100). It is shown that a bcc-like (100) structure is maintained throughout the layers after a recrystallization of the spacer layer by Fe/Si interdiffusion. Direct experimental evidence is presented that c-Fe1-xSi (

Apparent spin polarization decay in Cu-dusted Co/Al203/Co tunnel junctions

Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with ¿˜0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond ˜5 ML it becomes vanishingly small

Sign reversal of spin polarization in Co/Ru/Al2O3/Co magnetic tunnel junctions

Utilizing ultrathin Ru interfacial layers in Co/Al2O3/Co tunnel junctions, we demonstrate that not only does the tunnel magnetoresistance decrease strongly as the Ru thickness increases as found for Cu or Cr interlayers, in contrast, even the sign of the apparent tunneling spin polarization may be changed. Further, the magnitude and sign of the apparent polarization is strongly dependent on applied voltage. The results are explained by a strong density-of-states modification at the (interdiffused) Co/Ru interface, consistent with theoretical calculations and experiments on Co/Ru metallic multilayers and Co-Ru alloys

Asymmetric Pt/Co/Pt-stack induced sign-control of current-induced magnetic domain-wall creep

We report experimentally obtained magnetic domain wall (DW) velocities of current-assisted field-driven DW creep in perpendicularly magnetized Pt/Co/Pt. We have intentionally introduced an asymmetry in the stacks by using different thicknesses of the two Pt layers sandwiching the Co layer. Thereby, it is tested whether conflicting current-induced domain wall motion (CI-DWM) results may be intrinsically related to the basic layout and growth. We sketch a scenario which could be at the basis of contradicting reports in literature where the direction of CI-DWM conflicts with spin-torque-transfer theory, allowing the sign of the current-induced effect on DW motion to be tuned

Exchange interaction studies using epitaxially stabilized expanded fct-Mn(0 0 1)

It is demonstrated exptl. that expanded face centered tetragonal (e-fct) Mn, which is characterized by an axial ratio c/a > 1, can be stabilized by epitaxial growth on ferromagnetic (FM) fct Co(0 0 1) films. At room temp. this new metastable Mn phase is antiferromagnetically (AFM) ordered for thicknesses above the 2.5 monolayer, as inferred from AFM/FM magnetic exchange interaction studies. This crit. thickness does not depend on the magnetization direction of the FM layer. Even though for out-of-plane magnetized FM layers the coercivities are distinctly enhanced by the exchange interaction, no exchange bias can be detected. On the other hand, both coercivity enhancement and exchange biasing is obsd. for the in-plane magnetized FM/e-fct Mn bilayer. These results provide exptl. evidence that the AFM spin structure of e-fct Mn at the AFM/FM interface is confined to the film plane

NMR spectroscopy on Heusler thin films : a review

Heusler compounds exhibit different electronic ground states and functionalities, making them attractive materials for studies of their fundamental properties and for their technological exploitation. The high spin polarization, predicted in particular for Co2-based Heusler compounds, renders them prime candidates for electrode materials in spintronic devices such as giant magnetoresistance (GMR) elements or magnetic tunnel junctions and requires their implementation in thin film stacks. The growth of high quality Heusler films, however, demands their careful characterization. Typical issues in Heusler thin films are, besides the type and degree of structural order, the control of the film composition and the conservation of smooth interfaces between different layers in the film, e.g., between the Heusler layer and the tunneling barrier, while at the same time enabling high structural order. This review illustrates how nuclear magnetic resonance spectroscopy contributes to those issues by discussing recent examples of nuclear magnetic resonance studies of Heusler thin films

Nuclear magnetic resonance studies of materials for spintronic applications

Since its discovery in liqs. and also in solid matter in 1946, NMR (NMR) has been widely established as a std. tool for structural anal. of a wide range of materials. This review outlines recent NMR studies on materials considered to be useful in spintronic applications. Spintronics is a new research field which combines the use of both the charge and the spin of an electron as information carriers, which promises distinct advantages over conventional electronics which makes use only of the charge of electrons. A successful application of materials in spintronic devices requires a detailed knowledge of the interplay between the structure and the magnetic and electronic properties on an at. scale. NMR probes the local environments of the active nuclei. This local character of NMR arises from local contributions to the hyperfine field, namely, the transferred field which depends on the nearest neighbor atoms and their magnetic moments. This enables NMR to study the structural properties of bulk samples as well as of thin films of spin polarized materials. Moreover, NMR spectroscopy also provides an indirect tool to measure the d. of states of spin polarized materials via a measurement of the temp. dependence of the spin-lattice relaxation time. This review starts with an introduction into the basic concepts of NMR followed by a description of the important aspects of a pulsed NMR expt. Thereafter, information obtained by an NMR expt. is addressed. In the subsequent main part, selected recent NMR studies (published roughly after the year 2000) of materials for spintronic applications are presented including NMR studies of, for example, Co thin films, Heusler compds., double perovskites and pyrites