Magnetic multilayers

We have investigated the relationship between the magnetism and the magnetoresistance effect in the Co/Au, Ag multilayer films with layers produced in the atomic level by pulse electrodeposition method. The magnetoresistance effect is dependent on both the thickness of Co ferromagnetic layer and Ag,Au non-magnetic layers. The magnetization of these films shows the minimum value against the Ag and Au layer thickness. The Ag and Au layer thickness showing the maximum of MR ratio is not of necessary in
agreement with the Ag and Au layer thickness showing the minimum of magnetization. Antiparallel alignment of magnetic spin is a necessary but not sufficient condition in order to generate the GMR of multilayer films. For the Co/Au multilayer films, the Au layer thickness showing the minimum of the magnetization shifts to higher side of the Au layer thickness.

The magnetotransport properties of Ni 81 Fe 19 /W 90 Ti 10 multilayers are investigated. The effect of the thicknesses of the magnetic (Ni 81 Fe 19 ) and non magnetic (WTi) layers on the magnetoresistance (MR) are theoretically discussed in the framework of the Johnson-Camley semiclassical approach based on the Boltzmann transport equation. A comparison between the calculated and measured MR ratios is obtained. The observed MR ratio oscillates for WTi layer thickness with an average period of 10 Å. A weak MR(t NiFe ) ratio for a fixed t WTi is obtained and it presents a maxima peak of the MR with a value of 0.8% located at t NiFe = 50Å. In addition, electronic and magnetic properties of multilayers are investigated by self consistent ab initio calculations based on Korringa-Kohn-Rostocker (KKR). Spin polarized within the framework of the Coherent Potential Approximation (CPA) is considered for calculations.

The interface properties of Fe/MgO/Fe multilayer stack were investigated by using X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The magnetic
multilayers were deposited by electron beam evaporation method, which exhibits the attributes of
perpendicular magnetic anisotropy (PMA). XAS analysis shows that Fe-layer forms a Fe-O-rich
interface region with MgO-layer and a sum-rule analysis of the XMCD estimates the average
magnetic moment of 2.3160.1 lB per Fe-atom. XAS and XMCD studies indicate the formation
of a heterostructure (Fe/FeO/Fe2O3) on the interface. A phase transition in Fe-O stoichiometry
at interface is also observed at low temperature (90 K), which may be useful in magnetic storage
technology.

A full characterization of phase separation and the competition between phases is necessary for a comprehensive understanding of strongly-correlated electron materials (SCEM), such as under-doped high temperature superconductors 1,2 , complex oxide heterojunctions 3 , antiferromagnetic 4 and ferromagnetic 5 spinels, multiferroics 6,7 , rareearth ferroelectric manganites 8 , and mixed-valence manganites where phase competition is the dominant underlying mechanism governing the insulator-metal (IM) transition and the associated colossal magnetoresistance (CMR) effect 9-11 . Thin films of SCEMs are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to in-plane conduction paths. Accordingly, the correlated interactions in the out-of-plane (perpendicular) direction cannot be measured but only inferred. We address this shortcoming and show here an experimental technique in which the SCEM under study, in our case a 600 Å-thick (La 1-y Pr y ) 0.67 Ca 0.33 MnO 3 (LPCMO) film, serves as the base electrode in a metal-insulator-metal (MIM) trilayer capacitor structure. This unconventional arrangement allows for simultaneous determination of colossal magnetoresistance (CMR) associated with dc transport parallel to the film substrate and colossal magnetocapacitance (CMC) associated with ac transport in the Page 2 of 32 perpendicular direction. We distinguish two distinct strain-related direction-dependent insulator-metal (IM) transitions and use Cole-Cole plots to establish a heretofore unobserved collapse of the dielectric response onto a universal scale-invariant power-law dependence over a large range of frequency, temperature and magnetic field. The resulting phase diagram defines an extended region where the competing interaction of the coexisting ferromagnetic metal (FMM) and charge-ordered insulator (COI) phases 10-15 has the same behavior over a wide range of temporal and spatial scales. At low frequency, corresponding to long length scales, the volume of the phase diagram collapses to a point defining the zero-field IM percolation transition in the perpendicular direction.

We have studied the structure,the surface morphology, the magnetic domains and the magnetization of
ferromagnetic BaFeO3
-δ (BFO) thin films deposited on single-crystal MgO(001) substrate.The BFO film is
ferromagnetic-insulating at room temperature and shows a growth of self organized symmetric square-
shaped structures of various length-scales on the surface. The film, after oxygen annealing,shows several
pronounced modifications: (i)in addition to square structures, the pyramid-shaped structures also
manifest on the surface,(ii)the lattice parameter decreases indicating a change in the structure ,(iii) the
magnetization isotherms show magnetic anisotropy with a five-fold increase in magnetic coercivity and
two-fold increase in magnetic moment, and (iv) a larger growth of the magnetic domains. These results
demonstrate a strong influence of oxygen annealing on structural and magnetic properties of BFO films.
Our results suggest that the structural and the magnetic properties are strongly correlated in BFO films,
albeit with unaltered insulating state.

The effect of the AlOx barrier thickness on magnetic and morphological properties of Ta/Co/(AlOx)/Alq3/Si hybrid structures was systematically studied by means of atomic force microscopy, superconducting quantum interference device magnetometry, and nuclear magnetic resonance (NMR). All used techniques pointed out that the barrier thickness of 2 nm is required to obtain a magnetically good cobalt layer on top of Alq3.

Reduced spin transfer torque switching current density with non-collinear polarizer layer magnetization in magnetic multilayer systems Appl. Phys. Lett. 100, 252413 A study on exchange coupled structures of Fe/NiO and NiO/Fe interfaced with n-and p-silicon substrates J. Appl. Phys. 111, 123909 (2012) Origin of magneto-optic enhancement in CoPt alloys and Co/Pt multilayers Appl.

The micromagnetic continuum theory has been applied to perfect soft/hard multilayers characterized by antiferromagnetic interface coupling. The soft and hard phases have uniaxial anisotropy with a common direction, along which the external field is applied. The model assumes a nonuniform rotation of the magnetization, and it also considers an interface coupling that is reduced with respect to the strong-limit case. It is found that the deviation of the magnetization from the saturated antiparallel state can occur at two distinct nucleation fields, which mainly involve only one of the two phases. Moreover, in the case of a reduced interface coupling, the saturated parallel state becomes accessible and thus the nucleation from this state is taken into account. The critical equations have been deduced, allowing us to identify the conditions for which the nucleation regime changes from reversible to irreversible as a function of the intrinsic and extrinsic parameters. The results of the model, applied to a typical soft/hard system with planar anisotropy, have been summarized in suitable phase diagrams, as a function of the layer thicknesses and of the strength of the interface coupling. The analysis, supported by additional static and dynamic micromagnetic simulations, shows the occurrence of a rich variety of magnetization curves. As a secondary result we have found that, in the parallel nucleation process, the influence of the interface coupling extends inside the two phases to distances appreciably larger than the corresponding Bloch wall widths.

We discuss the basic assumptions underlying the stationary phase approximation to the interlayer exchange coupling between magnetic materials across nonmagnetic spacers. We show that, for temperatures and spacer thicknesses of interest, it cannot be applied to systems such as Fe/Ag/Fe and Fe/Au/Fe ͑001͒ trilayers. Such inadequacy results from particular confinement effects caused by the Fe layers in the Ag and Au extremal Fermi-surface ''neck'' states. This is of special relevance to the interpretation of experimental data.

The angular dependence of hysteresis loops of exchange-spring (ES) bilayers constituted by a Fe layer as the soft phase and a hard layer of L1 0 Fe 53 Pt 47 is presented. FePt thin films of nominal thickness 10 nm have been prepared by RF sputtering on MgO (1 0 0) substrates in order to achieve the epitaxial growth with the c-axis perpendicular to the film plane. The Fe soft layers have been deposited at RT with various thicknesses (from 2 to 10 nm). The angular dependence of the bilayers' magnetic properties is studied by SQUID magnetometry varying the angle between the easy axis of the hard phase and the direction of the applied field from 0 to p/2. The magnetic behavior at different angles is analyzed by a one-dimensional micromagnetic model specifically extended to the case of perpendicular magnetic anisotropy (PMA).

A full characterization of phase separation and the competition between phases is necessary for a comprehensive understanding of strongly correlated electron materials, such as under-doped high-temperature superconductors 1,2 , complex oxide heterojunctions 3 , spinels 4,5 , multiferroics 6,7 , rare-earth ferroelectric manganites 8 and mixed-valence manganites in which phase competition is the dominant mechanism governing the insulator-metal (IM) transition and the associated colossal magnetoresistance effect 9-11 . Thin films of strongly correlated electron materials are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to inplane conduction paths. We present an experimental study of anisotropic transport in phase-separated manganite thin films by using an unconventional arrangement of contact electrodes that enables the simultaneous determination of colossal magnetoresistance associated with d.c. transport parallel to the film substrate and colossal magnetocapacitance associated with a.c. transport in the perpendicular direction. We distinguish two distinct direction-dependent IM transitions and find a dielectric response that collapses onto a scale-invariant dependence over a large range of frequency, temperature and magnetic field.

The angular dependence of hysteresis loops of exchange-spring (ES) bilayers constituted by a Fe layer as the soft phase and a hard layer of L1 0 Fe 53 Pt 47 is presented. FePt thin films of nominal thickness 10 nm have been prepared by RF sputtering on MgO (1 0 0) substrates in order to achieve the epitaxial growth with the c-axis perpendicular to the film plane. The Fe soft layers have been deposited at RT with various thicknesses (from 2 to 10 nm). The angular dependence of the bilayers' magnetic properties is studied by SQUID magnetometry varying the angle between the easy axis of the hard phase and the direction of the applied field from 0 to p/2. The magnetic behavior at different angles is analyzed by a one-dimensional micromagnetic model specifically extended to the case of perpendicular magnetic anisotropy (PMA).

The exchange coupling between Fe layers separated by BCC Cu is calculated for Fe/Cu/Fe (001) trilayers. It is shown that the coupling is basically regulated by three extrema of the bulk BCC Cu Fermi surface. The contributions from those extrema are all of the same order of magnitude, but that associated with the "belly" at the Γ-point dominates. The calculated temperature dependence of the coupling varies considerably with spacer layer thickness. Individually, the amplitudes of these extrema contribution decrease with temperature, each according to a different rate. Such an effect may cause an actual increase of coupling with temperature for some Cu thicknesses. PACS:75.50.Fr., 75.30.Et., 75.50.Rr.

The angular dependence of hysteresis loops of exchange-spring (ES) bilayers constituted by a Fe layer as the soft phase and a hard layer of L10 Fe53Pt47 is presented. FePt thin films of nominal thickness 10nm have been prepared by RF sputtering on MgO (100) substrates in order to achieve the epitaxial growth with the c-axis perpendicular to the film plane.

The Anderson localization of light in one-dimensional disordered photonic superlattices is theoretically studied. The system is considered to be made of alternating dispersive and nondispersive layers of different randomthickness. Dispersive slabs of the heterostructure are characterized by Drude-like frequency-dependent electric permittivities and magnetic permeabilities. Numerical results for the localization length are obtained via an analytical model, only valid in the case of weak disorder, and also through its general definition involving the transmissivity of the multilayered system. Anomalous λ4- and  λ-4-dependencies of the localization length in positive-negative disordered photonic superlattices are obtained, in certain cases, in the long and short wavelength limits, respectively.

PACS: 78.67.Pt; 42.25.-p; 46.65.+g; 72.15.Rn

The dispersive part of the refractive index, 1− δ, of vanadium is determined by measuring the angular dependence of the Bragg peak at the V L2, 3 edge energy region using a Fe/V superlattice. This X-ray scattering technique provides access to the direct determination of the dispersive part of the refractive index across an absorption resonance and to the change of values from below unity to above unity.

A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully fabricated using different curing processes, forming a platform for integrated optical devices. The dual layer BCB polymer could potentially solve the high index contrast issue associated with existing glass-polymer structure, which require sub-micron precision when producing single-mode waveguides. Although the two BCB layers display similar physical properties, they have significantly different optical and chemical characteristics. The different curing processes for the undercladding and core layers led to these differences. Single mode waveguides fabricated via photolithography were also demonstrated with an average propagation loss of 2 dB/cm.