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Different models have been used to evaluate the interfacial Dzyaloshinskii–Moriya interaction (DMI) from the asymmetric bubble expansion method using magneto-optics. Here, we investigate the most promising candidates over a range of different magnetic multilayers with perpendicular anisotropy. Models based on the standard creep hypothesis are not able to reproduce the domain wall (DW) velocity profile when the DW roughness is high. Our results demonstrate that the DW roughness and the interface roughness of the sample layers are correlated. Furthermore, we give guidance on how to obtain reliable results for the DMI value with this popular method. A comparison of the results with Brillouin light scattering (BLS) measurements on the same samples shows that the BLS approach often results in higher measured values of DMI. [ABSTRACT FROM AUTHOR]

A method for detecting dc spin current propagation through an epitaxial antiferromagnetic (AFM) NiO layer is presented. Spin current is generated by spin pumping from an adjoining ferromagnetic (FM) layer and detected in a non-magnetic metallic layer by the inverse spin Hall effect. Comparison is made with a YIG/Pt bilayer, where only the Pt layer is electrically conducting, but for which spin Hall magnetoresistance makes an additional contribution to the measured signal. The signal obtained from the multilayered stack containing the AFM NiO layer is found to contain additional contributions due to anisotropic magnetoresistance. By exciting the sample with out-of-plane rf magnetic field and making measurements with a static field applied at different orientations within the plane of the sample, a signal associated with the dc spin current may be identified. [ABSTRACT FROM AUTHOR]

We demonstrate a Josephson junction with a weak link containing two ferromagnets with perpendicular magnetic anisotropy and independent switching fields in which the critical current can be set by the mutual orientation of the two layers. Such pseudospin-valve Josephson junctions are a candidate cryogenic memory in an all superconducting computational scheme. Here, we use Pt/Co/Pt/CoB/Pt as the weak link of the junction with d Co = 0.6 nm , d CoB = 0.3 nm , and d Pt = 5 nm and obtain a 60% change in the critical current for the two magnetization configurations of the pseudospin-valve. Ferromagnets with perpendicular magnetic anisotropy have advantages over magnetization in-plane systems, which have been exclusively considered at this point, as, in principle, the magnetization and magnetic switching of layers in the junction should not affect the in-plane magnetic flux. [ABSTRACT FROM AUTHOR]

Broadband ferromagnetic resonance responses for metallic single-layer and bilayer magnetic films with total thicknesses smaller than the microwave magnetic skin depth have been studied. Two different types of microwave stripline transducers were used to excite and detect magnetization precession: a coplanar waveguide and a microstrip line both with characteristic width larger than the free propagation path for traveling spin waves along the film. Both transducers show efficient excitation of higher-order standing spin wave modes across the film thickness in samples 30-91 nm thick. The ratio of amplitudes of the first standing spin wave to the fundamental resonant mode is independent of frequency for single-layer permalloy films. In contrast, we find a strong variation in the amplitudes with frequency for cobalt-Permalloy bilayers and the ratio is strongly dependent on the ordering of layers with respect to a stripline transducer. Most importantly, cavity ferromagnetic resonance measurements on the same samples show considerably weaker amplitudes for the standing spin waves. All experimental data are consistent with expected effects of eddy currents in films with thicknesses below the microwave magnetic skin depth. Finally, conditions for observing eddy current effects in different types of experiments are critically examined. [ABSTRACT FROM AUTHOR]

We report the thermal chemical vapor deposition of vertically-aligned multiwalled carbon nanotube forests directly onto electrically conductive cobalt disilicide (CoSi2) support using Fe as catalyst. We find that CoSi2 support layer is able to prevent the agglomeration of the catalyst and favor vertically-aligned growth better than a SiO2 support and comparable to an Al2O3 support. This is an unusual behavior for a conductive support. This is because CoSi2 has a lower surface energy than most metals or metallic compounds. This has great benefits in the application of CoSi2 as support for CNTs as horizontal and vertical interconnects. [ABSTRACT FROM AUTHOR]

The surface morphology, crystal structure, and in-plane magnetic anisotropy of sputter deposited Co70Fe30 films on GaAs(110) epilayer substrates have been investigated. The surface morphology of thin Co70Fe30 films appears to closely follow that of the underlying GaAs(110) substrate. The study of the crystal structure by x-ray diffraction shows that no crystallographic orientation other than Co70Fe30(110) is present in our films, although we cannot unambiguously deconvolute characteristic reflections of Co70Fe30(110) from those of GaAs(110) due to the very small lattice mismatch. High-resolution transmission electron microscopy shows that the crystal structure of the Co70Fe30 film is coherently matched to the GaAs(110) substrate. The magnetic anisotropies in both 35 and 1100 Å thick films are consistent with those of similar epitaxial films, and demonstrate that a strong bcc (110) texture is propagated throughout the entire film thickness. The cubic and uniaxial anisotropy constants extracted by fitting with the Stoner–Wohlfarth model are consistent with those of molecular beam epitaxy grown bcc CoxFe(100-x)/GaAs(110). This work shows that sputter deposition may be used to produce structurally coherent bcc-Co70Fe30/GaAs(110) contacts suitable for spin-injection applications. [ABSTRACT FROM AUTHOR]

We have developed magnetic nanostructures which comprise two thin film Ni81Fe19 pads of differing coercive field connected by a nanoscale constriction. In the region of field between the two coercive fields, a domain wall nucleates in the constriction and the resistivity associated with this wall is determined by comparing electrical measurements with micron scale magneto-optic measurements. There is an excellent correspondence between the field region where the wall nucleates and the change in magnetoresistance, which is dominated by anisotropic magnetoresistance. Shape optimization of the pads gives a larger field range over which the domain wall is stable. [ABSTRACT FROM AUTHOR]

Self-assembled arrays of nanospheres have been used to pattern a Co/Pt multilayer into nanopillars. On top of this has been deposited a Co/Ru multilayer, which is antiferromagnetically coupled. The nanopillars introduce a known structural and magnetic lateral modulation into the multilayer. Soft x-ray magnetic scattering was used to observe the interference patterned from the patterned substrate. This has allowed us to show how the magnetic roughness correlates with the structural roughness and obtain selective magnetometry of the various magnetic elements. [ABSTRACT FROM AUTHOR]

Epitaxial Fe48Rh52 thin films of nominal thickness 500 Å were grown on MgO (001) substrates via molecular beam epitaxy and capped with 20 Å of either Au or MgO. The presence of the anticipated magnetostructural phase transition from antiferromagnetism to ferromagnetism at ∼350 K was confirmed by superconducting quantum interference device and magneto-optic Kerr effect magnetometry. X-ray magnetic circular dichroism (XMCD) experiments were carried out at the L2,3 edges; measurements were done in both total electron yield (TEY) mode and indirect transmission mode. At room temperature, the indirect transmission XMCD data show no detectable dichroism, consistent with bulk antiferromagnetic behavior. However, room-temperature TEY data originating from the films’ surface reveal an appreciable dichroic signal indicating the presence of ferromagnetism. This near-surface/interfacial magnetism may be modified by choice of capping layer; the MgO-capped sample exhibited a considerably smaller ferromagnetic XMCD signal. The results have potential impact on the application of FeRh thin films as temperature-variable pinning layers in exchanged-biased systems. [ABSTRACT FROM AUTHOR]

In order to optimize their magnetic properties, Fe/Au multilayers were treated by pregrowth and postgrowth ion-beam bombardments. The ferromagnetic resonance linewidth was used as our main figure of merit. The pregrowth treatment of the MgO substrate using a 60 eV atomic oxygen beam resulted in a reduction of the inhomogeneous linewidth broadening in comparison with a sample grown on an untreated substrate. This homogeneity increase is linked to the removal of substrate carbon contamination by the chemically active oxygen. It correlates with the reduced interface roughness. The postgrowth sample irradiation using 30 keV He+ ions also reduces the inhomogeneous broadening in the linewidth. Fe and Au have a miscibility gap, but the demixing is kinetically quenched at room temperature. Ion collisions locally minimize the interface energy by providing the energy necessary for localized demixing, resulting in a smoothing effect. Combined, the pregrowth and the postgrowth irradiations lead to the lowest observed linewidth. [ABSTRACT FROM AUTHOR]

The in-plane magnetic properties of Co0.7Fe0.3 films sputtered onto Al0.1Ga0.9As and Al0.1Ga0.9As/GaAs epilayers are consistent with a strongly oriented bcc crystal structure with clean metal-semiconductor interfaces. However, the interface induced uniaxial magnetic anisotropy is oriented along one of the in-plane <100>, rather than <110>, as is the case in molecular beam epitaxy—grown films. Resonant x-ray measurements show interfacial magnetic disorder in films on Al0.1Ga0.9As, which accounts for the difference in magnetic anisotropy behavior between samples on Al0.1Ga0.9As and Al0.1Ga0.9As/GaAs epilayer substrates, and which may have significant consequences for the spin-injection efficiency across such interfaces. [ABSTRACT FROM AUTHOR]

Tapered coplanar waveguides with integrated photoconductors were designed, fabricated, and measured, with pulsed transmission results comparing well with High Frequency Structure Simulator simulations which predict increased confinement and electric field concentration in the tapered region. Devices made with titanium/gold metallisation were used to demonstrate transmission and confinement, while the magnetoresistive properties of devices with cobalt/copper multilayers were used to demonstrate the field concentration. In the latter case, a mathematical framework was developed to understand the relationship between tapering effects and the picosecond magnetoresistance response. [ABSTRACT FROM AUTHOR]

Tunneling magnetoresistance spectroscopy measurements have been performed on spin-valve magnetic tunnel junctions where the free magnetic electrode is a Cu38Ni62 alloy with a Curie temperature of around 240 K. These measurements allow us to follow the temperature dependence of the energy of the bottom of a minority-spin band close to the Fermi energy, which is partly responsible for the tunneling conductance. The temperature dependence of the tunneling spin polarization of the CuNi electrode has also been extracted using the Julliere formula. We show that the tunneling spin polarization as a function of temperature can be related to the temperature-dependent magnetization using an extension of the commonly applied Stearns model that incorporates the motion of the band close to the Fermi level. This model reproduces the nonlinear relation between tunneling spin polarization and magnetization obtained for Cu38Ni62. [ABSTRACT FROM AUTHOR]

We have performed in situ transport measurements on CoFeB/AlO/Co spin-valve magnetic tunnel junctions during annealing up to 200 °C. For optimally oxidized junctions we observe a marked decrease in the parallel state junction resistance, which occurs at around 150 °C and continues throughout the anneal process until the temperature is reduced back below 150 °C. Spectroscopic measurements reveal a stronger bias dependence due to enhanced magnon-assisted tunneling, and show that features relating to weak fcc texture in the cobalt upper electrode fade after annealing at 200 °C. We attribute this to a possible amorphization of the cobalt electrode in close proximity to the barrier interface. [ABSTRACT FROM AUTHOR]

The postdeposition annealing of magnetic tunnel junctions has become standard practice in junction fabrication to improve barrier properties. We have performed tunneling measurements at elevated temperatures during the annealing process on plasma-oxidized, MgO barrier, magnetic tunnel junctions. The data were interpreted in terms of the Hartman model which accounts for an asymmetric barrier profile. The results could not be interpreted solely by the temperature smearing of the Fermi distribution and so the electrode/barrier/electrode structure had been altered during the annealing. While the barrier height at one interface improved, the other was degraded. Our experiments lead us to believe that this is due to the diffusion of Mn to the barrier/pinned electrode interface. We show that through transport and tunneling magnetoresistance measurements it is possible to monitor physical processes such as material migration during the annealing process. [ABSTRACT FROM AUTHOR]

Fe3O4 /GaAs hybrid structures have been studied using reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), x-ray magnetic circular dichroism (XMCD), and low-temperature vibrating-sample magnetometry (VSM). The samples were prepared by oxidizing epitaxial Fe thin films in a partial pressure of 5×10-5 mbar of oxygen at 500 K for 180 s. Clear RHEED patterns were observed, suggesting the epitaxial growth of Fe oxides with a cubic structure. The XPS spectra show that the oxides were Fe3O4 rather than γ-Fe2O3, as there were no shake-up satellites between the two Fe 2p peaks. This was further confirmed by the XMCD measurements, which show ferromagnetic coupling between the Fe cations, with no evidence of intermixing at the interface. The VSM measurements show that the films have a magnetic uniaxial anisotropy and a "quick" saturation property, with the easy axes along the [011] direction. This detailed study offers further insight into the structure, interface, and magnetic properties of this hybrid Fe3O4 /GaAs(100) structure as a promising system for spintronic application. [ABSTRACT FROM AUTHOR]

Ultrafast demagnetization has been studied in Si/Pt(160 Å)/[Co25Ni75(x)/Pt(8 Å)]20 (x=3, 4.5, and 6 Å) multilayers with perpendicular anisotropy by magneto-optical pump-probe measurements in the polar geometry. Time-resolved measurements made in the saturated state showed that maximum demagnetization was achieved within 300 fs. Hysteresis loops were measured at a time delay of 1.3 ps for temperatures from 20 to 300 °C. The Curie temperature was found to increase from 150 to 250 °C with increasing Co25Ni75 thickness. By comparing the loops obtained with and without pump excitation, the increase in electron temperature due to the pump was estimated to be about 60 K. [ABSTRACT FROM AUTHOR]

Femtosecond optical pump-probe experiments were performed upon a Ni(720 Å)/Si(100) sample in the polar geometry with the pump beam close to normal incidence. A signal due to the ultrafast demagnetization effect was observed when the pump pulse was linearly polarized. When the pump was elliptically polarized, additional peaks were observed at zero time delay, resulting from the specular inverse Faraday effect (SIFE) and the specular optical Kerr effect (SOKE). By comparing measurements made with different pump helicities, the SIFE and SOKE peaks and the demagnetization signal were found to superpose in a linear fashion. From the dependence of the peak height upon the pump polarization, values of χxxyy=(1-3i)×10-10 rad cm3 erg-1 and χxyyx=(-9+2i)×10-12 rad cm3 erg-1 were deduced for the nonvanishing components of the local cubic susceptibility tensor. For applied fields less than the saturation value, the sudden reduction of the thin film demagnetizing field leads to an imbalance of the torques acting upon the magnetization, causing it to precess. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron scattering mechanisms within metallic multilayers are affected by both structural and magnetic disorders. Off-specular x-ray scattering has long been used to probe the structural interfaces, and it is only recently that it has been applied to the study of magnetic disorder. We compare the resonant magnetic x-ray scattering with off-specular neutron studies from magnetron-sputtered Co/Cu and Co/Ru multilayers grown at the second antiferromagnetic coupling peak. Both techniques yield similar results for the Cu system, and a simple domain model can be applied to extract the magnetic interface morphological parameters. For the Cu system, the in-plane correlation length is field dependent and is 880 ± 20 Å after saturation along the hard axis, but increases to 7000 ± 100 Å after saturation along the orthogonal easy axis. Both systems show strong out-of-plane correlations in both the structural and magnetic disorders. In all cases, the out-of-plane correlation length for the structural interfaces is 200-250 Å, but the ratio of the magnetic to structural correlations length is dependent on the magnitude of the exchange coupling and ranges from 0.4 to 1.4. [ABSTRACT FROM AUTHOR]

We have measured the magnetic domain patterns in Co/Pd multilayers of varying thickness using magnetic force microscopy in the presence of an external magnetic field applied perpendicular to the multilayers. We find that the domain patterns evolution is in qualitative agreement with existing theories for single layer thin films. Our results are in reasonable agreement with a theoretical model of domains appropriate to multilayer films. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The role of the density of states in the giant magnetoresistance (GMR) of ferromagnet 1 (FM1)/nonmagnetic (NM=Cu)/ferromagnet 1 (FM1) sandwiches has been investigated by inserting a thin layer of the second ferromagnetic material (FM2=Co) at the FM1/Cu interfaces. As the thickness of the inserted layer increases, the GMR increases to a value seen for purely Co/Cu/Co sandwiches. By using differing FM1 materials [e.g., Py (permalloy (Ni[sub 80]Fe[sub 20]), Ni, Fe] we observe the exponential increase in GMR as more Co is inserted to be dependent on the FM1 material behind it. This is explained by realizing that although the GMR is dominated by the scattering caused by defects like those at the FM2 material/Cu interface, the nature of the scattering depends on the density of states of the FM1 material. This result is discussed in terms of advanced theories on the origin of the GMR in magnetic multilayers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have measured the field dependence of the magnetoresistance MR(H) in the CPP mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co (10 Å)/Cu/Co (60 Å)/Cu][sub N] and [Co (10 Å)/Cu][sub N] [Co (60 Å)/Cu][sub N], with the Cu layers always being 200 Å. The series resistor model predicts that in the CPP mode, MR(H) is independent of the ordering of the layers. Nevertheless, the MR(H) curves measured were found to be completely different for the two cases. We suggest that the reason for this difference is that the electron mean free path is long enough that the potential that scatters the electrons is due to pairs of neighboring magnetic layers, which differ for the two types of magnetic multilayers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Conventional spin valves consist of two magnetic layers, one of which is pinned by exchange bias to act as a reference magnetic layer in giant magnetoresistance measurements. Antiparallel biased spin valves feature a Co/Ru/Co trilayer in place of this pinned layer, where the Co layers are strongly antiferromagnetically coupled. This leads to hugely enhanced pinning since an applied field will exert opposite torques on the Co layer moments. Spin valves are typically deposited in a magnetic field to define magnetic anisotropies, and the development of magnetic structure in the pinned AF couple is not trivial under these conditions. The resultant moment of the AF couple is found to slowly rotate as the final Co layer is deposited. This results in canted pinning once the exchange bias layer is added. There appears to be some magnetic friction as the Co layers rotate during growth. The rotation means that the pinning direction can take any angle with respect to the growth field, leading to positive or negative (or even orthogonal) exchange bias. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The observed magnetotransport properties of magnetically coupled multilayers depends not only on the nature of the magnetic coupling but also the magnetic domain correlations and disorder. Neutron scattering gives access to the magnetic coupling through the specular reflectivity and the domain correlations through the diffuse scattering. Sputtered multilayers of Co/Cu and Co/Ru have been investigated as a function of the applied magnetic field. A simple domain model relates the observed scattering to the domain correlation length and the magnetic disorder. In both systems highly vertically correlated magnetic domains are observed with in-plane correlation lengths, at remanence, of 1.5 and 7 μm for the Cu and Ru systems, respectively. In both systems the Co domains order antiferromagnetically across the nonmagnetic spacer. The remanent vertically correlated state is recovered after saturating the sample. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present measurements on hybrid ferromagnetic/semiconductor devices. Single, submicron ferromagnetic structures have been fabricated directly onto the surface of a semiconductor, which incorporates a near-surface two-dimensional electron gas (2DEG). The induced Hall resistance and magnetoresistance of the 2DEG are used to measure the magnetic properties of the stripes directly. The relative merits of these two techniques are compared using a device geometry in which both types of measurement can be made simultaneously. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Charge transfer at metallo-molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc-C60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo-carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp3 orbitals are annealed into sp2-π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz-π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices. [ABSTRACT FROM AUTHOR]

We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80 nm, with the Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics. [ABSTRACT FROM AUTHOR]

Studies the spin-dependent scattering in the nonmagnetic layers of annealed cobalt and copper multilayers. Problems in the measurement of the buried interfaces in a multilayer; Preparation of the sample; Discussion on the results of the study.

Deals with a study which developed a method for changing the magnitude of giant magnetoresistance in magnetic multilayers through the deposition of chromium and gold impurities. Experimental details; Results; Information on magnetization studies.

Reports on the observation of a giant magnetothermopower (GMT), giant magnetoresistance (GMR) and on magnetization measurements in cobalt/copper superlattices grown by molecular beam epitaxy. Value of the GMT at room temperature; Association of the maximum values of both the GMT and GMR with saturation fields and remnant magnitizations; Relationship between the magnetoresistance and the magnetothermopower.

Deals with a study wherein cobalt nuclear magnetic resonance studies of the effect of annealing molecular beam epitaxy on grown cobalt and copper multilayers have been undertaken. Methods; Results; Discussion.

The magnetic properties of exchange biased systems deposited on top of fullerene-based materials have been studied. An enhanced exchange bias field has been observed for Si/SiO2/C60/Co/Cu/Co/IrMn/Ta and Si/SiO2/FeC60/Co/Cu/Co/IrMn/Ta in comparison to a typical structure of Si/SiO2/Ta/Co/Cu/Co/IrMn/Ta. Here the magnetic properties of the devices are changed significantly with an organic underlayer or seed layer. The magnetic ordering is well maintained, and C60 seeding results in an exchange bias of (19.5 \pm 0.5) mT, some 7 mT higher than that of Ta seeded spin valves (12.5 \pm 0.5 mT). A combination of MOKE (magneto-optical Kerr effect), X-ray diffraction and Raman spectroscopy have been used to characterize the materials and further understand the interactions between the Co and fullerene-based materials. [ABSTRACT FROM AUTHOR]