Effects In Magnetic Multilayers Research Articles

Microstructure of spin-valve mr sandwiches

Giant magnetoresistance ( GMR ) effects in magnetic multilayers with spin-valve structures are under intensive investigation. The GMR effects in spin-valve structures originate from the change in the orientation of magnetization in the successive ferromagnetic layers. Of the various types of spin-valve multilayered structures reported, spin-valve sandwiches, in which one of the two ferromagnetic layers separated by a nonferromagnetic metal layer is constrained through exchange coupling to an adjacent antiferromagnetic layer, are most promising for applications in read heads for high density magnetic recording. This is due to their large MR and high sensitivity in low magnetic fields. Study of the correlation between magnetic/magnetotransport properties and the microstructure of spin-valve sandwiches is crucial for a better understanding of the mechanism of the spin-valve effects and for future MR heads design. Here, we present the results of transmission electron microscopy (TEM) studies of the microstructure of a Ni81Fe19(47Å)\Cu(18Å)\Ni81Fe19(53Å)\FeMn(186Å) spin-valve sandwich.

Polar magneto-optics in simple ultrathin-magnetic-film structures.

For a better understanding of optical interactions in magnetic layered structures we establish general expressions of both polar Kerr and Faraday first-order magneto-optical (MO) effects. The approach presented here enables the MO response of an arbitrary magnetic layer system to be analytically expressed with an accuracy practically equal (less than ${10}^{\mathrm{\ensuremath{-}}4}$ deg) to that of the full matrix calculations usually employed for modeling MO effects in magnetic multilayers. The formulas for any particular structure are obtained from general MO expressions by introducing associated reflection and transmission coefficients. This procedure is justified here in the simple case of an ultrathin magnetic film sandwiched between two nonmagnetic layers. These accurate expressions are further simplified for ultrathin magnetic films and the limitations of this approximation discussed. The simplified formulas are then used to analyze MO polar Kerr and Faraday data in well-defined Au (5 nm)/Co/Au (25 nm) structures, grown on float glass substrates. The Co layer thicknesses are chosen in the range 0.4--2.0 nm to preserve a perpendicular magnetic anisotropy. The simplified expressions, as well as the numerical modeling of the trends in MO spectra with a variation of the overlayer or buffer layer thicknesses, show that the shape of the polar Kerr effect spectrum is mainly dependent upon the optical properties of the Au buffer layer whereas the observed MO amplitudes are reduced consistently with the absorption of the Au overlayer.

Extraordinary Hall effect in magnetic multilayers.

The extraordinary Hall resistivity of magnetic multilayers is derived by using the Kubo formalism. It is found that the commonly used scaling relation between the extraordinary Hall resistivity and the ordinary resistivity is not valid. Hall voltages in the plane of the layers and perpendicular to the plane of the layers are quite different, just as the ordinary resistivities are different for these two geometries. Recent experimental results are discussed within this formulation.

Semiclassical theory of perpendicular transport and giant magnetoresistance in disordered metallic multilayers.

The effect of disordered interfaces and bulk impurities on perpendicular transport in metallic multilayers is considered in an effective-mass semiclassical approximation. The transmission matrix is obtained by diagrammatic perturbation theory in terms of the effective-mass and conduction-band profiles at the interface. In the weak-scattering limit specular and diffuse scattering give equally important contributions to the conductance. Predictions for the transport properties of interfaces with low concentrations of strongly scattering defects should be accessible to verification by experiments. The transition from fully ballistic (Sharvin) to diffuse transport (Drude) is described analytically both in two- and three-dimensional systems, where the former case is of relevance for transport in the two-dimensional electron gas in semiconductor heterostructures. The theory is applied to the spin-valve effect in magnetic multilayers. The magnetoconductance is described by a simple formula in terms of the mean free path for the majority- and minority-spin electrons.

Perpendicular transport through rough interfaces in the metallic regime

Perpendicular transport through an interface in the metallic regime is considered. The semi-classical theory presented is based on the Landauer-Büttiker formalism taking into account an effective mass mismatch at the interface and a non-zero average of random scattering potentials. The transmission probability for a given mode is found in terms of the effective mass and the conduction band bottom to the left and to the right of the interface, the Fermi energy, the self-energy of the electron, and the transverse wave vector of the electron. The diffuse and specular contributions to the interface roughness scattering are shown to be equally important in the weak scattering limit. Predictions for the transport properties of interfaces with a low concentration of strongly scattering defects should be accessible to verification by experiments. The theory is applied to the spin-valve effect in magnetic multilayers.

Biquadratic Effects in Magnetic Multilayers with Low-Field Giant MR

Biquadratic Effects in Magnetic Multilayers with Low-Field Giant MR

Anomalous Hall effect in magnetic multilayers

We have studied the field dependence of the Hall resistivity in Fe/Cr multilayer films at 4.2 K. The observed anomalous Hall resistivity is composed of both negative skew-scattering and positive side-jump components. The conduction electron scattering responsible for the giant magnetoresistance is accompanied by large left-right asymmetry.

Control of interlayer magnetic coupling and magnetoresistance in magnetic multilayers by insertion of very thin magnetic layer

Changes in magnetoresistive characteristics and in magnetization hysteresis curves with the insertion of very thin magnetic layers at interfaces between Cu spacer layers and magnetic layers are studied in Cu/Co, Cu/NiFe, and Cu/Co/Cu/NiFe multilayers. It was found that the interlayer magnetic coupling is strongly affected by covering the surfaces of magnetic layers with another type of magnetic layer a few angstroms thick. The possibility of controlling the magnetoresistance effect in magnetic multilayers using this phenomenon is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>