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Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, their wave-like nature allows for novel computing paradigms. Conventional methods to detect spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser. In this Article we demonstrate magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700 nm using a diffraction-limited laser spot with a size of 10 $\mu$m in 20 nm thick Py strips. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing wavevector-selective spin-wave detection. This should open up new avenues towards the integration of the burgeoning fields of photonics and magnonics, and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research., Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, their wave-like nature allows for novel computing paradigms. Conventional methods to detect spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser. In this Article we demonstrate magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700 nm using a diffraction-limited laser spot with a size of 10 μm in 20 nm thick Py strips. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing wavevector-selective spin-wave detection. This should open up new avenues towards the integration of the burgeoning fields of photonics and magnonics, and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research.

We report an experimental study which focuses on the magneto-optic interaction between light and perpendicularlymagnetized ferromagnetic thin-film multilayers. In this study, samples containing multiple Co/Pt interfaces are measured via the polar Magneto-Optic Kerr Effect (MOKE).Thanks to a sample set with a continuous Co thickness variation, and single and double Co layered samples, interface and bulk contributions to the magneto-optic activity areseparately determined. Kerr rotation and ellipticity signals are recorded as a function of the Co thickness. The results are analyzed via a transfer matrix method that accounts for the standard optical and magneto-optic effects in multilayered thin-films. Bulk magneto-optic contribution of Co (QCo;bulk) that is in accordance with literature is consistently determined despite the use of thin-films. Interfacial Co (QCo;int:) and magnetized Pt (QPt) contributions are presented in terms of two models. Interface phenomena of the large spin-orbit coupling between Co and Pt and the proximity induced magnetization in Pt layer are represented in the models. The strength of interfacial magneto-optic activity is interpreted as an indicator of the relative interface quality among the samples.

A magnetic-field-dependent resistance change of eight orders of magnitude is observed in boron-doped Si-SiO2-Al structures. In order to identify the elementary mechanisms governing this phenomenon, the thickness of the oxidic layer, which is used as an interface energy barrier, has been varied by changing the exposure time to an oxygen plasma. Next, the chemical composition has been monitored by in situ x-ray photoelectron spectroscopy measurements. From current-voltage measurements, we observe that at low temperatures, an ultrathin SiO2 layer provides the kinetic energy to trigger an autocatalytic process of impact ionization. A magnetic field suppresses the onset of impact ionization to higher electric fields, resulting in a large magnetoresistance.

Fine-crystalline diamond particles are grown on standard Si atomic force microscopy tips, using hot filament-assisted chemical vapor deposition. To optimize the conditions for diamond deposition, first a series of experiments is carried out using silicon substrates covered by point-topped pyramids as obtained by wet chemical etching. The apexes and the edges of the silicon pyramids provide favorable sites for diamond nucleation and growth. The investigation of the deposited polycrystallites is done by means of optical microscopy, scanning electron microscopy and micro-Raman spectroscopy. The resulting diamond-terminated tips are tested in ultra high vacuum using contact-mode atomic force microscope on a stepped surface of sapphire showing high stability, sharpness, and hardness.

Recently it has been observed that the magnetoresistance (MR) of plasma oxidized exchange biased Co/Al2O3/Co tunnel junctions can have a strongly asymmetric bias voltage (Vbias) dependence. In this article we report on the dependence of this phenomenon on barrier oxidation time tox. For junctions based on 1.5 nm Al, tox was varied from 20 to 120 s. For tox = 20 s, for which the MR is approximately 20% at Vbias = 0, and for tox = 90 s symmetric MR(Vbias) curves are found, with the MR decreasing monotonically with |Vbias|. A strong asymmetric bias voltage dependence was observed for intermediate oxidation times, which correspond to essentially full oxidation of the Al layer, but almost no formation of stoichiometric CoO at the bottom electrode. Samples with tox = 60 s show even an asymmetric double peak in MR(Vbias). Due to its strength, it has an important consequence for device applications: for a series of junctions with variable tox the maximum signal voltage (at a fixed current) is not necessarily obtained for junctions which have the largest MR ratio at Vbias = 0. ©2001 American Institute of Physics.

Due to their very thin tunnel barrier layer, magnetic tunnel junctions show dielectric breakdown at voltages of the order of 1 V. At the moment of breakdown, a highly conductive short is formed in the barrier and is visible as a hot spot. The breakdown effect is investigated by means of voltage ramp experiments on a series of nominally identical Co/Al2O3/Co tunnel junctions. The results are described in terms of a voltage dependent breakdown probability, and are further analyzed within the framework of a general model for the breakdown probability in dielectric materials, within which it is assumed that at any time the breakdown probability is independent of the (possibly time-dependent) voltage that has been previously applied. The experimental data can be described by several specific forms of the voltage breakdown probability function. A comparison with the models commonly used for describing thin film SiO2 breakdown is given, as well as suggestions for future experiments.

We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni 80 Fe 20 /Fe 50 Mn 50 bilayers grown on Cu~110! single-crystal substrates. An enhancement of the exchange bias field, H eb , up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [110] to [001].

Time-resolved magnetization modulation spectroscopy (TIMMS) is proposed as a new probe of the ultrafast spin dynamics in a wide range of magnetic media. This pump–probe technique offers a high magnetic sensitivity by imposing a high frequency modulation to the circular polarization of the pump beam. The resulting modulated magnetization is reflected in an oscillating magneto-optical signal, and is picked up using a lock-in scheme. Experimental details are discussed and a theoretical modeling of the detected signals in a TIMMS experiment is presented. We applied TIMMS to the spin dynamics of CdTe/CdMnTe quantum well structures at room temperature. A spin scattering time of 10–15 ps is found, almost independent of the photon energy, whereas additional time scales (

We present x-ray diffraction (XRD) investigations of the structure of nominally lattice-matched GaInAs/InP multiple quantum well (MQW) structures grown by chemical beam epitaxy (CBE). To obtain information about the individual MQW layers and the interface structure we make use of the x-ray interference effect between two layers of equal lattice constant but different layer thickness separated by ultrathin strained (interfacial) layers. This effect predicted by the dynamical diffraction theory provides a powerful tool to quantitatively investigate ultrathin single quantum well structures and monolayer thin interfaces as well as MQW structures. For a given switching sequence during CBE growth, we determine the interface structure of GaInAs/InP MQW structures within the limits given by XRD theory. Additionally we found that an As gradient from the GaInAs quantum well layers into the InP barrier layers is present. The influence of the substrate off-orientation, the growth rate, and the group V flux in the InP barriers on the total amount of strain incorporated into the InP layers is shown. The obtained results indicate that the mechanism of As incorporation into InP layers is similar to the mechanism observed for the As incorporation into (qua)ternary GaxIn1-xAsyP1-y layers.

The frequency dependence of the magnetic permeability as well as of the electrical impedance have been investigated for soft-magnetic granular FeHfO thin films. The impedance measurements indicate that capacitive effects resulting from the inhomogeneous structure of the layers are of no importance for the roll off of the permeability of the present films. The frequency behavior at various FeHfO thicknesses shows that eddy current effects start to play a role above thicknesses of 10 μm. Below this thickness ferromagnetic resonance dominates the roll off.

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction.

The switching field interval, ¿Hs, of Ni–Fe–Co-based thin films and spin-valve layered structures, sputter-deposited on a Ta-buffer layer, was studied. The switching field interval is the field range in which the magnetization reversal of a ferromagnetic layer takes place. In thin films, ¿Hs is determined by the uniaxial anisotropy, induced by growth in a magnetic field. This anisotropy increases with the ferromagnetic layer thickness and saturates at a thickness of 10–25 nm. It also depends on the alloy composition as well as on the choice of the adjacent layers. In exchange-biased spin valves, an additional contribution to ¿Hs was observed, which increases monotonically with increasing interlayer coupling. We explain this in terms of the effect on the magnetization reversal of the sensitive layer due to a simultaneous small, but temporary, magnetization rotation in the exchange-biased layer and lateral variations of the interlayer coupling. In addition, the effect of biquadratic coupling on ¿Hs is discussed. Finally, the thermal stability of ¿Hs is investigated.

In recent years, it was discovered that the current through an organic semiconductor, sandwiched between two non-magnetic electrodes, can be changed significantly by applying a small magnetic field. This surprisingly large magnetoresistance effect, often dubbed as organic magnetoresistance (OMAR), has puzzled the young field of organic spintronics during the last decade. Here, we present a detailed study on the voltage and temperature dependence of OMAR, aiming to unravel the lineshapes of the magnetic field effects and thereby gain a deeper fundamental understanding of the underlying microscopic mechanism. Using a full quantitative analysis of the lineshapes, we are able to extract all linewidth parameters and the voltage and temperature dependencies are explained with a recently proposed trion mechanism. Moreover, explicit microscopic simulations show a qualitative agreement to the experimental results. (C) 2013 AIP Publishing LLC.

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)]

Point contact Andreev reflection measurements show a correlation between measured spin polarization and the interface scattering parameter Z extracted from fits of the modified Blonder–Tinkham–Klapwijk model to the conductance–voltage curves of superconductor/ferromagnet point contacts. We present a simple spin–flip scattering model which identifies Z2 as the effective scattering parameter and explains the observed exponential decay of the spin polarization.

The oxidation process of Co/AlOx/Co magnetic tunnel junctions has been investigated by photoconductance, in addition to traditional transport measurements. The shape of the photoconductance curves is explained within the framework of a simple qualitative model, assuming an oxidation time dependent imbalance of the incident forward and reverse hot electron fluxes, as well as inelastic scattering processes in the oxide. Due to the large sensitivity of the technique, the presence of unoxidized Al beneath the barrier layer can be monitored very accurately. The disappearance of a negative contribution to the photocurrent indicates the complete oxidation of the barrier layer, which coincides with the maximum magnetoresistance. From a Fowler analysis, the barrier height is determined as a function of oxidation time. The observed disagreement of the effective barrier heights determined by this technique and those found by Simmons fits demonstrates the added value of photoconductance studies.

Real-time in situ optical measurements were performed during the oxidation of ultrathin Al layers with a view to study oxidation kinetics and provide process control. The optical technique combines high temporal and spatial resolution with submonolayer sensitivity. In situ x-ray photoelectron spectroscopy measurements on the same samples are in good agreement, confirming the accuracy and sensitivity of the technique. For all thicknesses studied, the initial oxidation is extremely rapid, with quasilogarithmic behavior over the whole time scale. This technique could be utilized to study a wide variety of in situ reactive processes.

Theoretical studies of the temperature dependence of the tunneling magnetoresistance ratio (TMR) are presented. A successful elastic tunneling model has been extended to handle temperature dependence. It treats Fermi smearing and applies Stoner-like behavior to the exchange split band structure in the electrodes to calculate TMR(T). As expected, the effects of Fermi smearing are small, but small changes in the magnetic band structure produce large changes in TMR. For a Co/I/Co junction produced by LeClair et al. [Phys. Rev. Lett. 84, 2933 (2000)], calculations using bulk magnetization predicted 33% of the experimental loss of TMR from 0 to 300 K with only a 1.5% change in magnetization. A mere 3.2% change in magnetization produced 100% of the observed drop in TMR. These results imply larger than imagined intrinsic temperature dependence for TMR. ©2001 American Institute of Physics.

We have studied the biquadratic exchange coupling in epitaxially grown Fe/Si/Fe. The temperature and thickness dependence of the biquadratic coupling strength were determined unambiguously by fitting the easy- and hard-axis magneto-optical Kerr effect loops. The origin of the biquadratic coupling can be fully understood in terms of Slonczewski's loose spins mechanism.

An optical polarization modulation technique was adapted to provide a simple, fast, and flexible method for studying the kinetics and growth characteristics of thin oxide layers, using Al2O3 as an example. The optical technique allows precise determination of the amount of remaining metallic Al as a function of the initial Al thickness, while scanning a laser spot across the wedge. Optical data suggest that the oxide growth rate for the ultrathin layers may be dependent on the specific microstructure. In situ x-ray photoelectron spectroscopy performed on homogenous samples confirmed the interpretation of the optical results. ©2000 American Institute of Physics.

Recent studies show that the magnetic properties of epitaxial thin films of magnetite (Fe3O4) deviate strongly from bulk behavior: it is difficult to saturate thin films, ultrathin films may become super paramagnetic, their saturation magnetization drops to zero, and the local magnetic moments are oriented out of plane in zero field. The possible relationship between this anomalous behavior and the occurrence of anti-phase boundaries (APBs) is discussed. Transmission electron microscopy images confirm that APBs are present in our Fe3O4 films grown by molecular beam epitaxy on MgO(100). Only APBs with out-of-plane shift vectors are visible. The much higher APB density found in sputtered films suggests that preparation conditions are important. To explain the deviating saturation and the superparamagnetic behavior of thin Fe3O4 films at the same time, the magnetic coupling over the APB must be dramatically reduced due to spin disorder along the boundaries.

The magnetic behavior and structure of Fe3O4/MgO multilayers have been investigated with Mossbauer spectroscopy in field, magnetization measurements, and scanning tunneling microscopy. It is shown that detailed structural knowledge of the size of the structural domains and the width of the antiphase boundaries are indispensable in understanding the magnetization behavior of the films and the contradictory results reported in the literature.

In this paper we report the soft magnetic properties of thin films of sputtered MnZn ferrite deposited on thermally oxidized Si substrates. A high deposition temperature, 600¿°C, together with the addition of water vapor to the sputtering gas was found to improve the initial ac permeability, µ. The highest value obtained was approximately 30. For MnZn-ferrite films with much larger grain sizes, as obtained by deposition on a polycrystalline Zn-ferrite substrate, a µ of 100 was obtained. The results are discussed in terms of the so-called nonmagnetic grain boundary model.

An analysis of the complete dielectric tensor of bulk magnetite, Fe3O4, and of Fe3O4 substituted with a variable degree of Mg2+ or Al3+ allowed the assignment of the main magneto‐optical (MO) transitions in Fe3O4 between 0.5 and 4.0 eV. This assignment is consistent with our reinterpretation of the MgFe2O4 and Li0.5Fe2.5O4 MO‐Kerr spectra. An analysis of the stoichiometry of a thin Fe3O4 layer is made, based on the Kerr spectrum, which is compared to an analysis based on the Verwey transition. The Kerr spectrum is also used to compare wavelengths for MO‐Kerr effect studies of wedge‐shaped samples.

A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness has been observed. The Co thickness dependence displays two clear peaks consistent with the recently predicted oscillation period of 6.2 Å Co. Apart from the two peaks also several small peaks are visible on a scale of about 1 monolayer Co. Free-electron calculations indicate that these rapid variations in strength may result from slight differences between the slopes and starting points of the two Co wedges that were involved in the experiment. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Thin films of Co and Co/Cu/Co trilayers with wedged Cu interlayers were grown epitaxially on Cu buffer layers on hydrogen passivated Si(001) wafers. We find that single Co layers have a well-defined four-fold anisotropy but with smaller in-plane anisotropies than observed in Co grown on Cu crystals. Ruderman–Kittel–Kasuya–Yosida (RKKY) interlayer coupling is observed in one Co/Cu/Co sample which is the smoothest of the films as measured by atomic force microscopy. Some of the films also form a dot-like structure on the surface. Intermixing at elevated temperatures between the Cu buffer and Si limits the ability to form flat surfaces to promote RKKY coupling.

We report on a novel approach to establish switchable pinning of magnetic domain walls in a nanowire with perpendicular magnetic anisotropy by a single in-plane magnetized single-domain nanomagnet positioned on top of the wire. Devices were prepared by depositing a permalloy nanomagnet on top of a nanowire formed from a Co/Ni multilayer with their long axes parallel, separated by a nonmagnetic layer. We show by electrical measurements that the domain wall pinning strength depends critically on the state of the bistable nanomagnet and can differ by more than 10 mT. We also performed micromagnetic calculations that show that the difference in pinning strength is caused by the interaction of the forced Neel wall with the nanomagnet's magnetostatic field.

We investigated the electronic and vibrational properties of magnetite at temperatures from 300 K down to 10 K and for pressures up to 10 GPa by far-infrared reflectivity measurements. The Verwey transition is manifested by a drastic decrease of the overall reflectance and the splitting of the phonon modes as well as the activation of additional phonon modes. In the whole studied pressure range the down-shift of the overall reflectance spectrum saturates and the maximum number of phonon modes is reached at a critical temperature, which sets a lower bound for the Verwey transition temperature T$_{\mathrm{v}}$. Based on these optical results a pressure-temperature phase diagram for magnetite is proposed., Comment: 5 pages, 4 figures; accepted for publication in J. Appl. Phys

In order to explain a number of recent experimental observations of laser-induced femtosecond demagnetization in the large fluence limit, we discuss the consequences of a recently proposed nonlocal approach. A microscopic description of spin flip scattering is implemented in an effective three temperature model, including electronic heat diffusion. Effects of finite film thickness on the demagnetization transients are discussed. Our results show a clear saturation of the ultrafast demagnetization, in excellent agreement with experimental observations.

We report on the change in the structural and magnetic properties of magnetically soft ternary Co80-xFexB20 alloys as a function of composition, thickness, and annealing temperature. Compositions high in cobalt show a significant change in coercivity after annealing. This is explained using the random anisotropy model by relating the magnetic exchange length to the grain size of the crystallites. The presented results are a systematic study explaining trends seen in the transition from soft to hard magnetic behavior, providing insight into why the soft CoFeB alloys have been so successful recently in spintronic devices.

The influence of current pulses on the domain structure of a 2 µm wide wire composed of a soft out-of-plane magnetized magnetic material is studied by high spatial resolution nonintrusive magnetic imaging. The injection of current pulses (1012 A/m2) leads to stable magnetic states composed of two domains with opposite magnetization direction separated by a domain wall parallel to the wire. The direction of the magnetization in the domains is reversed back and forth by applying successive current pulses with opposite polarity. The formation and control of the domain states by the current is attributed to the effect of the Oersted field, which is calculated to be large enough to induce the switching.

Recent spin echo nuclear magnetic resonance (NMR) revealed that the half-metallic Co2Mn1-xFexSi Heusler alloys exhibit the L21 structure with random distribution of Mn and Fe on the 4b Wyckoff position. This random distribution is most prominent in the third coordination shell of the 55Mn nuclei, as this shell is the first magnetically active shell, leading to a line splitting in the 55Mn NMR spectra. A comparison, as presented in this paper, of all 55Mn NMR satellite lines shows that the resonance frequencies corresponding to the same number of Fe atoms in the third shell of 55Mn shift to slightly different resonance frequencies with increasing overall Fe content x. This shift is related to the constructive contribution of higher shells to the hyperfine field. These higher shells affect also the satellite linewidth, leading to a parabolic behavior with increasing Fe concentration x. This parabolic behavior is modified by the frequency spacing related to the replacement of Mn by Fe.

A sign change of the organic magnetoresistance effect is observed as a function of temperature. There is a large difference in the IV behavior when the sign of the magnetoresistance (MR) is positive compared to when the sign of the MR is negative, pointing to the possibility that the sign change of the MR is due to a change in the charge transport mechanism. The positive and negative MRs show different characteristic field widths B0 in the MR versus magnetic field curves. Also, the traces with positive MR show a clear temperature dependence of B0 while no systematic dependence on temperature is seen in the traces with negative MR. This behavior can be qualitatively explained by the recently proposed bipolaron model.

We have studied the dependence of the electron in-plane g factor and spin decoherence time on the built-in elec. field (Ei) at the position of a single layer of self-assembled (In, Ga)As/GaAs quantum dots (QDs). Control of Ei is achieved by inducing screening charges in a p-i-n GaAs matrix with a continuous wave (cw) laser. Using a time-resolved pump-probe technique to measure the spin dynamics via the magneto-optical Kerr effect, we observe a large hole spin decoherence time of 440 ps. Measurements as function of the cw laser power and, thus, of Ei show that the electron spin decay time in the QDs depends strongly on Ei and decreases from 310 to 110 ps with increasing Ei. We attribute this effect to increasing tunneling rates of electrons out of the QDs at high Ei. We observe a slight increase of the electron g factor from 0.40 +- 0.03 to 0.46 +- 0.04 with increasing Ei, which might be a result of a changing wavefunction as a result of a different confinement potential due to Ei.

The response of a ferromagnet/antiferromagnet exchange coupled bilayer to femtosecond laser heating is studied by means of pump-probe time-resolved magneto-optical Kerr effect (TR-MOKE) in the polar geometry on a Co (10nm)∕IrMn (0–15nm wedge) sample. When an external field is applied in the film plane, perpendicular to the exchange bias direction, a damped precessional motion of the ferromagnetic spins can be triggered by laser excitation. We observe that the exchange bias field HEB,dyn, extracted from the TR data, systematically differs from the value HEB,st, obtained by static MOKE loop measurements, for thin (

We investigated the efficiency and formation mechanism of ammonia generation in recombining plasmas generated from mixtures of N2 and H2 under various plasma conditions. In contrast to the Haber-Bosch process, in which the molecules are dissociated on a catalytic surface, under these plasma conditions the precursor molecules, N2 and H2, are already dissociated in the gas phase. Surfaces are thus exposed to large fluxes of atomic N and H radicals. The ammonia production turns out to be strongly dependent on the fluxes of atomic N and H radicals to the surface. By optimizing the atomic N and H fluxes to the surface using an atomic nitrogen and hydrogen source ammonia can be formed efficiently, i.e., more than 10% of the total background pressure is measured to be ammonia. The results obtained show a strong similarity with results reported in literature, which were explained by the production of ammonia at the surface by stepwise addition reactions between adsorbed nitrogen and hydrogen containing radicals at the surface and incoming N and H containing radicals. Furthermore, our results indicate that the ammonia production is independent of wall material. The high fluxes of N and H radicals in our experiments result in a passivated surface, and the actual chemistry, leading to the formation of ammonia, takes place in an additional layer on top of this passivated surface.

In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1 eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface.

We examine the role of Mn diffusion in the thermal stability of tunneling spin polarization P by directly measuring P of Al/AlOx/Co/FeMn and Al/AlOx/Co90Fe10/FeMn junctions using superconducting tunneling spectroscopy (STS). We confirm Mn diffusion in our junctions using x-ray photoelectron spectroscopy after an ultrahigh vacuum 500 °C anneal. Surprisingly, and in contrast to the current belief, no drop in P is observed using STS. Therefore, though Mn diffuses significantly, it cannot be solely responsible for the drop in tunneling magnetoresistance observed after postdeposition anneals above 300 °C. ©2005 American Institute of Physics

A systematic study has been conducted on the dependence of the magnetoresistance (MR) ratio on the barrier thickness in TaOx-based magnetic tunnel junctions. The relatively low MR ratio (

A method for back-tracing magnetic field pulses in pump-probe-type magnetization dynamics measurements is presented. Solving vectorially the Landau–Lifshitz–Gilbert equation for our field-induced measurement geometry yields field pulse profiles fulfilling the theoretical expectations on a 100 ps timescale. Applying the method to our earlier, all-optical-type pump-probe measurements, the claim that the optical pulse triggers an ultrafast anisotropy field pulse gets a direct proof: we derive a pulse consisting of a delta-peak type, full width at half maximum

At the boundary of a ferromagnetic material, the local change in the surroundings of the atomic magnetic moments induces an additional magnetic anisotropy. The dipole-dipole interaction, responsible for the form-dependent demagnetizing field inside the ferromagnet, differs for magnetic moments at the boundary and magnetic moments inside the bulk material. By calculation it is shown that the demagnetization factor for an ultrathin ferromagnetic film is thickness dependent. However, the anisotropy resulting from the dipole-dipole interaction can be interpreted as a surface and a volume anisotropy which depend on the crystalline structure and orientation of the film, but are independent of the thickness of the film.

A Mössbauer study of Fe3-xAlxO4 and Fe3-xGaxO4 has been undertaken. Measurements at low temperatures in magnetic fields enabled us to better separate the Fe(A) and Fe(B) subspectra and to determine the cation distribution on tetrahedral and octahedral sites. Whereas Al up to x=1.4 shows a strong preference for B sites, giving rise to a normalization of the spinel structure with Fe2+ located mainly in tetrahedral sites, Ga distributes over both A and B places without tendency towards normalization at least below x¿1.2.

Zero‐field muon spin relaxation (μSR) experiments have been performed on the spin glass Fe1.75Ti1.25O5. Above the spin‐glass temperature of 44 K a distinct exponential μSR rate (λ) is observed, while below T g a square‐root exponential decay occurs, indicating fast spin fluctuations. Near 8 K, a maximum in λ is indicative of transverse spin ordering. The low λ values and the sharp λ peak at T g are very promising for the study of spin freezing models like the Vogel–Fulcher law or the power law.