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Presents information on a study which observed grazing incidence nuclear multilayer diffraction of synchroton radiation from a periodic stack of alternating iron 56 and 57 layers. Methodology of the study; Results and discussion on the study; Conclusions.

Investigates the hysteresis properties of ultrathin ferromagnetic films. Characteristics of the film at low temperature; Discussion on the role of roughness in the hysteresis properties of ferromagnetic ultrathin films; Model of wall motion which provides an explanation of the overall observations.

Provides information on a study which measured the magnetic properties of nickel/gold multilayer films prepared by magnetron sputtering on glass substrates. Experiment; Results and discussion; Conclusion.

Time-resolved x-ray magnetic circular dichroism was used to investigate ferromagnetically coupled CoFe/Ru/NiFe bilayers. The magnetization dynamics was driven by a continuous wave excitation. The precessional motion of the individual layers was detected separately by tuning the x-ray photon energy to the L3 absorption edge of either Ni or Co. Using two different waveguide stack geometries in-phase and antiphase excitation could be selected showing its effect in the measured precessional signal of the individual layers. In exchange-coupled bilayer two precessional modes were observed for each layer. The relative phase angles of the magnetic response between the two layers were found to be 8° and 133°, for the two modes revealed their quasiacoustic and quasioptic character. [ABSTRACT FROM AUTHOR]

The magnetization dynamics of each layer of interlayer exchange coupled Ni81Fe19/Ru(t)/Co90Fe10 films was investigated by time resolved x-ray magnetic circular dichroism (TR-XMCD) after pulsed excitation. The coupling was changed from ferromagnetic to antiferromagnetic by variation of the Ru thickness t. The precessional motion of the individual layers was detected separately by measuring the XMCD signal at the L3 absorption edge of either nickel or cobalt. From the observation of two frequency components in the precession of both layers in samples with negligible interlayer exchange coupling, the presence of a different coupling mechanism was concluded. Using two different sample geometries, the influence of antiphase and in-phase excitation on the triggered dynamics was studied. [ABSTRACT FROM AUTHOR]

Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR), as well as quasistatic methods such as a magneto-optic Kerr effect magnetometer and a vibrating sample magnetometer, have been used for complementary studies of interlayer exchange coupled Si/Ta/NiFe(30 nm)/Ru(t)/NiFe(30 nm)/Ta films of variable Ru thickness t. The coupling constants were determined from the measured magnetization curves by fitting them to simulated ones. The dynamics measurements revealed two spin wave modes, which could be identified as optical and acoustical ones. The optical mode changes significantly with the coupling, whereas the slight change of the acoustical mode is due to different relative orientations of the layer magnetizations. Numerical simulations helped to identify optical and acoustical modes. The intensity of these two modes changes with the bias field and coupling. Using VNA-FMR the optical mode could be observed up to higher bias fields than with the PIMM at small excitation angles. While varying the pulse field up to 150 Oe using the PIMM, the intensity ratio of optical and acoustical modes changed and additional modes occurred. [ABSTRACT FROM AUTHOR]

Spin-wave theory predicts reduced thermal spin-wave excitations due to a magnetic anisotropy. Recent results show that a strong uniaxial in-plane anisotropy in ultrathin Fe/GaAs(001) films indeed stabilizes the ferromagnetic order versus thermal spin excitations [Kipferl et al., J. Appl. Phys. 97, 10B313 (2005)]. In order to study whether a fourth-order in-plane anisotropy has a similar effect epitaxial Fe70Co30/Au(001) samples with zero magnetocrystalline anisotropy were studied and compared to results for Fe/Au(001). The temperature dependence of the spontaneous magnetization MS for T<0.5Tc can be well described by the Bloch [Z. Phys. 61, 206 (1930)] T3/2 law in the entire thickness range. However, for each thickness B is reduced in Fe70Co30/Au(001) compared to Fe/Au(001) films despite the reduced anisotropy. This means that the effect of a weak in-plane anisotropy is overcompensated by the enhanced exchange interaction. [ABSTRACT FROM AUTHOR]

Epitaxial Fe(001) films with thicknesses less than 20 monolayers were grown on epitaxial Au(001) surfaces by molecular beam epitaxy. All films have a fourfold anisotropy and a negligible uniaxial component. In contrast, the magnetic behavior of Fe films on GaAs(001) is governed by a superposition of a dominating uniaxial and a fourfold anisotropy component. The temperature dependence of the spontaneous magnetization MS for T<0.5TC can be well described by Bloch's T3/2 law for both systems. With decreasing film thickness the spin wave parameter B increases significantly compared to the bulk in both cases. However, for the same thickness B is reduced in Fe/GaAss001d compared to Fe/Au(001) films. This is attributed to the presence of the strong uniaxial anisotropy in Fe/GaAs(001) which apparently stabilizes the ferromagnetic order against thermal excitations. [ABSTRACT FROM AUTHOR]

A pulsed inductive microwave magnetometer (PIMM) is used to examine magnetization dynamics. The thin film sample is brought into close proximity to the coplanar waveguide, which allows for simple changing of samples. The angle between the easy axis (e.a.) and field direction can easily be varied by rotation of the sample on the waveguide. The magnetization dynamics, i.e., precessional frequency, decay time, and precessional amplitude, are determined with respect to this angle or the bias field for epitaxial Fe1-xCox films with different anisotropies. The two precessional motions of a magnetic double layer (FeCo/Au/Ni80Fe20) where resolved with the PIMM, which is promising for future investigations on exchange coupled layers. [ABSTRACT FROM AUTHOR]

Dot arrays with dots of well-defined circular shape have been patterned from epitaxial Fe films on GaAs(001). Magnetization reversal and temperature dependence of the spontaneous magnetization were studied by superconducting quantum interference device magnetometry, an alternating gradient magnetometer and the magneto-optical Kerr effect. It was observed that Bloch T3/2 law is valid for all dot diameters. The spin wave parameter B increases with a decrease in dot diameter by a factor of 4, which reduces the magnetization at room temperature by about 25% compared to its value at 10 K for the smallest dots. From this observation it is concluded that additional excitation modes are present in the spin system. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thermal spin excitations in confined ferromagnetic structures become increasingly important, e.g., because they reduce tunnel magnetoresistance in highly integrated magnetic memories and the stability of stored information. Here, the effect of lateral confinement on the temperature dependence of magnetization in ultrathin films was studied. Epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy. Patterning into dot arrays with several million dots of well defined circular shape was accomplished by electron beam lithography, lift-off, and ion beam etching. The magnetic properties of the samples were investigated by superconducting quantum interference device magnetometry between 10 and 350 K. All films-in addition to the fourfold magnetocrystalline anisotropy-have an in-plane uniaxial magnetic anisotropy with the easy axis along [110], which is fully conserved during patterning. The temperature dependence of the spontaneous magnetization for T<0.5T[SUBC] can be well described by Bloch's law, M[SUBS](T) = M(0)(1 - BT[SUP3/2]), for all samples. For a dot diameter of 500 nm the spin wave parameter B is significantly increased compared to the extended 14 ML film, which in turn shows about twice the bulk value of B[SUBFe] = 5 &times 10[SUP-6] K[SUP-3/2]. The enhancement of spin wave excitations with decreasing film thickness and lateral dimension is discussed in comparison to existing theories and model simulations. [ABSTRACT FROM AUTHOR]

Couplers in general serve for galvanically isolated signal transmission between sensitive equipment. Standard opto-couplers are generally limited to a bandwidth of 25 MHz. However, with ever-increasing data transfer rates the need for couplers with much higher bandwidth is steadily growing. For this purpose magneto-couplers are very promising because their bandwidth is expected to be limited only by the Larmor precession of the magnetic moments with frequencies in the range of 1-10 GHz. In magneto-couplers the signal to be transmitted is converted into a current through a micro-coil. The resulting magnetic field is detected by a giant magnetoresistance (GMR) sensor element separated by an isolation layer. In the present case this element is a Wheatstone bridge consisting of four spin valves. The voltage across the bridge resulting from the magnetization change of the soft layers due to the field pulses is detected with a 1 GHz storage oscilloscope. Present experiments indicate a bandwidth larger than 500 MHz. After proper termination of the signal paths and applying a dc-bias field the rise time of the input signal of less than 1 ns is not increased by the coupler. Furthermore we show that the driving pulse may be completely reproduced in shape by applying external dc-bias fields. It will also be discussed how capacitive and inductive crosstalk between the coil and the spin valves and nonideal termination of the signal paths affect the achievable bandwidth. [ABSTRACT FROM AUTHOR]

The magnetocrystalline anisotropy of epitaxially grown bcc-Fe(001) films on GaAs(001) shows a transition from a fourfold intrinsic anisotropy in thick films to an uniaxial one in ultrathin films (<3 nm) and hence can be tuned by varying the film thickness. Here we investigate the consequence of such an anisotropy tuning for the magnetization configurations of nanomagnets. The thickness was varied between 2.5 and 30 nm in steps of 2.5 nm. Disks with diameters between 200 nm and 2 μm were patterned with electron beam lithography and ion beam etching. The remanent and ac-demagnetized states as well as the switching behavior were examined by magnetic force microscopy. In addition, we employed micromagnetic simulations to compare with the measured results. [ABSTRACT FROM AUTHOR]

Undulation instabilities of magnetic domains have been observed in nanostructured strips of a ferromagnetic Fe/Gd multilayer. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, was used for imaging. Below a critical magnetic field, sinus-like modulations of the magnetic domains could be observed. At a higher rate of field induced strain rectangular patterns occur. They seem to be characteristic for the reduced lateral width of the magnetic system and are in contrast to chevron patterns observed in extended systems. The domain morphologies found in different magnetic fields H, and in nanowires of various widths L[sub z], have been summarized in a H-L[sub z] "phase" diagram. An analogy with theoretical predictions for extended systems could be found. [ABSTRACT FROM AUTHOR]

In order to prepare submicron sized particles with strong magnetocrystalline anisotropies high quality epitaxial bcc-Fe films were grown on GaAs(110) and GaAs(001) by molecular beam epitaxy. Whereas Fe(ll0) on GaAs(ll0) is a model system with uniaxial in-plane anisotropy, Fe(001) on GaAs(001) has a strong fourfold anisotropy for films thicker than ∼5 nm. Various shapes like circular, square, or rectangular elements with sizes from 200 nm up to 6/µm were fabricated by electron beam lithography and ion beam etching. The remanent states after saturation along different directions or ac demagnetization along the easy axis were examined by using magnetic force microscopy. The experimental results clearly reflect the interplay of the different magnetocrystalline and shape anisotropies depending on the different magnetic histories. [ABSTRACT FROM AUTHOR]

It was shown previously that ultrathin Fe films epitaxially grown on GaAs(001) exhibit a strong in-plane uniaxial magnetic anisotropy which turns out to be a pure interface contribution with an anisotropy constant K[sub U, sup S], expressed as an energy per unit area, which is constant in a wide thickness range. However, for films thinner than ∼10 monolayers (ML), K[sub U, sup S] decreases with decreasing thickness when measured at 300 K. In order to eliminate effects of thermal excitations, Fe(001) films grown on GaAs(001) by molecular beam epitaxy were investigated by superconducting quantum interference device magnetometry at low temperature. The extrapolated room temperature values and the ground state data both indicate that K[sub U, sup S] vanishes at t = 2.5 ML. This is the thickness at which the onset of ferromagnetism takes place, i.e., where the Curie temperature T[sub C] becomes nonzero. This might be interpreted as a verification of the Mermin-Wagner theorem in the sense that long-range ferromagnetic order is stabilized by the magnetic anisotropy. It is discussed whether the onset of ferromagnetism is indeed triggered by the appearance of magnetic anisotropy or if there is a common origin of both phenomena. Finally, it is found that the uniaxial anisotropy does not vanish at T[sub C], but persists up to temperatures of ∼1.5 T[sub C]. This means that K[sub U, sup S] does not scale with a certain power of the spontaneous magnetization. The disparity between the persistence of the anisotropy above T[sub C] and its disappearance below the critical thickness of 2.5 ML is discussed. [ABSTRACT FROM AUTHOR]

The in-plane magnetic anisotropy of Fe films epitaxially grown on GaAs(001), in addition to a thickness-dependent four-fold contribution has a uniaxial component originating from the Fe/GaAs interface. This has been observed in several previous investigations. The orientation of the uniaxial easy axis (e.a.), however, was found to be along the [110] direction in most studies, but also an e.a. parallel to [-110] was reported in a few cases. It has been suggested that different reconstructions of the GaAs surface prior to Fe deposition could be responsible for this discrepancy. In the present contribution, it is shown that in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature the uniaxial anisotropy always has its easy axis along [110] with practically the same magnitude. In particular, the surface reconstruction of the GaAs substrate either (4×2) or (2×6) — has no effect on the resulting uniaxial magnetic anisotropy. This [together with recent results related to the phase transition of Fe/GaAs(001)] suggests that the same atomic configuration is formed at the Fe/GaAs(001) interface in both cases connected with the segregation of a certain amount of As (and Ga) to the surface. [ABSTRACT FROM AUTHOR]

Epitaxial Fe[sub 1-χ]Co[sub χ] alloy films with χ=0.22 and χ=0.33 were grown on GaAs(001) by molecular-beam epitaxy in a thickness range of 3 to 80 monolayers (ML). The magnetic properties were investigated by magneto-optic Kerr effect. Ferromagnetic order at room temperature was observed for thicknesses above 4 ML. The in-plane magnetic anisotropy of all films is a superposition of a uniaxial component with the easy axis along [110], which is not discussed here, and a four-fold contribution. The effective uniaxial and four-fold anisotropy constants, K[sup eff, sub U] and K[sup eff, sub 1], were determined by fits to the hard axis magnetization loops. K[sup eff, sub 1] contains an interface and a volume term which lead to a linear variation of K[sup eff, sub 1] with the inverse film thickness. It turns out that the surface and volume anisotropy constants are of opposite sign for all alloy compositions causing a sign reversal at a critical thickness, t[sub crit]. This critical thickness seems to be a universal value, which is caused by a general proportionality between the volume and the interface anisotropy constants with the same negative constant of proportionality for Fe[sub 1-χ]Co[sub χ]/GaAs(O01), Fe/Au(001), and Fe/Ag(001). This behavior of the four-fold anisotropy constants is consistently explained within Néel's pair energy model for a body-centered-cubic ferromagnet. [ABSTRACT FROM AUTHOR]

Ultrathin Fe films were epitaxially grown at room temperature on GaAs(001) with either predominant (4x2) or (2x6) surface reconstruction. At nominal Fe coverages of t[sub Fe]>=2.8 monolayers (ML), a ferromagnetic state is observed below a certain critical temperature, T[sub C]. Surprisingly, the magnetic phase transition at T[sub C] appears even sharper than for Fe films on metallic single-crystal substrates, which were believed to be an excellent representation of two-dimensional (2D) ferromagnets. This may be due to the extremely short lateral length scale of film inhomogeneities. The critical exponent β=0.26 is close to the value expected for 2D XY systems of finite size. For t[sub Fe]=3.6 ML, T[sub C] is close to room temperature. T[sub C] decreases steeply with decreasing Fe coverage, with an average slope of 270 K/ML. From a power law extrapolation, T[sub C] seems to vanish at t[sub Fe]=2.5 ML. The onset of ferromagnetism at t[sub Fe]=2.5 ML is interpreted as! a percolation phenomenon during the coalescence process of Fe islands. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Epitaxial Fe films in a thickness range from 4 to 64 monolayers (ML) were grown by molecular beam epitaxy on GaAs(110) at room temperature. The growth was characterized by reflection high energy electron diffraction. The magnetic in-plane anisotropy was investigated by alternating gradient magnetometry in a temperature range from 150 to 295 K. For a 64 ML thick Fe(110) film the [001] axis is the easy axis, the [-110] the intermediate axis, and the hard axis is between [-110] and [-111]. For Fe films with a thickness below 24.2±1.2 ML the [-110] becomes an easy axis at room temperature. A 24 ML Fe film shows a reorientation of the easy axis with decreasing temperature: Above the critical temperature of (251±3) K [-110] is the easy axis, for lower temperatures it becomes an intermediate axis. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic transmission x-ray microscopy is a novel technique to image element specifically magnetic domain structures. A lateral resolution down to 25 nm is provided by the Fresnel zone plates used as optical elements in soft x-ray microscopy. The magnetic contrast is given by x-ray magnetic circular dichroism, i.e., large magnetic contributions up to 25% to the absorption cross section of circularly polarized x rays that occur in the vicinity of, e.g., the Fe L[sub 3,2] edges (706 and 719 eV) and depend on the relative orientation of the projection of the magnetization of the sample onto the photon propagation direction. Thus, both in-plane and out-of-plane contributions to the magnetization are accessible. Here we present images of the magnetic domain structure of a (3 nm Cr/50 nm Fe/6 nm Cr) thin film system with a preferentially in-plane magnetization recorded at the Fe L edges. The samples have been prepared by thermal evaporation onto a 100 nm thin Si[sub 3]N[sub 4! ] membrane and were mounted under a tilt of 30° with respect to the transmission direction of the photons in the full-field microscope. Corresponding images taken under a tilt of 0° ruled out out-of-plane contributions. Images recorded in applied varying external magnetic fields allowed to study the switching behavior. These trial results have a large impact on further investigations of nanostructured magnetic systems, e.g., spintronic devices and magnetic sensors with magnetic soft x-ray microscopy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)x75 multilayered FeGd system has been prepared on a 30 nm thin Si[sub 3]N[sub 4] membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record t! he images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electric transport through magnetic tunnel junctions (MTJs) has been studied at various temperatures to gain understanding of the transport mechanisms in such devices. Between 15 and 400 K, MTJs with Al[sub 2]O[sub 3] barriers have been tested at low voltage (barrier height: 2.0-2.1 eV, barrier width: 1.5 nm). For the soft-magnetic electrode a sputtered 1 nm Co/6 nm Fe double layer was used. The hard-magnetic electrode is realized with a 1.5 nm Co/1.0 nm Cu/1.0 nm Co system. Antiferromagnetic coupling between the two Co layers leads to a high saturation field. The 1.5 nm Co layer is used as the second electrode of the MTJ. The conductance increases with growing temperature while the tunnel magnetoresistance (TMR) shows a slight decrease. For interpretation of the results, the temperature dependence of direct tunneling, of the hopping conductance via trapped states, and of the interface magnetization have to be taken into consideration. The dominant factor for the TMR is! proportional to 1-BT[sup 3/2] and follows the temperature dependence of the interface magnetization. The experimental data allow us to separate transport mechanisms and characterize the junction quality. At room temperature the spin-independent hopping conductance of our junctions is calculated to be less than 10% of the total conductance. Concerning the magnetic properties, a ferromagnetic orange-peel coupling corresponding to a field of about 4 Oe (0.3 kA/m) was found at 15 K, which decays exponentially with increasing temperature to less than 0.6 Oe (0.05 kA/m) at 300 K. The coercive field of the soft layer also shows an exponential decay. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Epitaxial Fe[sub 34]Co[sub 66] films in a thickness range from 3 to 100 monolayers (MLs) were grown by molecular beam epitaxy on GaAs(001) at room temperature. The growth was characterized by reflection high energy electron diffraction and x-ray diffraction. The magnetic properties were investigated by alternating gradient magnetometry magneto-optic Kerr effect, and superconducting quantum interference device magnetometry. The films show a strong interface-induced uniaxial in-plane anisotropy with the easy axis along [110]. In addition, the fourfold anisotropy coefficient changes sign around 6 ML i.e., the easy axis of the fourfold anisotropy switches from <110> to <100> with decreasing thickness. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The morphology, atomic magnetic moments, and in-plane magnetic anisotropies of ultrathin bcc Fe(001) films deposited by molecular beam epitaxy on ZnSe epilayers grown on GaAs(001) single crystal are reported. The growth mode and structure have been determined in situ by means of reflection high energy electron diffraction and Auger electron spectroscopy. The magnetic properties were characterized ex situ by an alternating gradient magnetometer, superconducting quantum interference device (SQUID) magnetometry, and conversion electron Mo¨ssbauer spectroscopy (CEMS). The Fe growth is epitaxial and occurs by three dimensional nucleation at the beginning. The coalescence of the islands is observed around 7 monolayers (ML). In agreement with SQUID results, CEMS measurements indicate no reduction of the Fe magnetic moment compared to the bulk value even for the first Fe monolayers. Determination of the in-plane anisotropy constants as function of the Fe thickness shows a strong interface-induced uniaxial in-plane magnetic anisotropy, which leads to a continuous evolution from a pure uniaxial anisotropy with easy axis along [110] direction for thickness below 10 ML to the pure bulk cubic Fe anisotropy above 40 ML. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A multilayered FeGd system sputtered on a Si[sub 3]N[sub 4]-membrane was used to demonstrate that magnetic transmission x-ray microscopy enables the imaging of the domain structure with high resolution in a quantitative way and in varying external magnetic fields. The field-dependent evolution of sub-100 nm out-of-plane magnetized domains, i.e., the transition from stripe into bubble domains, could be observed in detail. It has been shown that critical fields like the bubble collapse field can be described by a wall energy model. Contrary to the assumption of the theory, the magnetization does not remain perpendicular to the film plane in all cases. This is only true inside the bubbles. In the stripe domains the magnetic moments rotate. Their angle could be measured as a function of the external applied field. Internal stray fields can cause a rotation of moments leading to a contrast at the edges of stripe domains. The results indicate that the magnetization reversal in 3d/4f multilayers is not only determined by wall motions and is therefore more complex than previously assumed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In order to study sub-100-nm domains in magnetic multilayers a combination of three high-resolution imaging techniques has been applied to the same samples for the first time: magnetic force microscopy (MFM), Lorentz microscopy with a transmission electron microscope, and magnetic transmission x-ray microscopy (MTXM). The samples—atomically stacked [Fe(001)/Au(001)][sub n] multilayers with an approximate L1[sub 0]-lattice—were prepared by molecular beam epitaxy (MBE) on a GaAs(001) substrate which was then locally removed by laser-induced wet etching to create a window that is transparent for 200 keV electrons and soft x-rays. Magnetization curves with perpendicular and in-plane applied field indicate a spontaneous perpendicular magnetization with an equilibrium domain pattern in small fields and reversible wall motion. About 60 nm wide domains could be observed with MFM and MTXM, respectively. Lorentz images did not show any in-plane magnetic contrast, but the domain pattern appeared when the sample was tilted. This indicates that the magnetization is indeed strictly perpendicular. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High quality epitaxial Fe films were grown on GaAs(001) by molecular beam epitaxy and magnetron sputtering. Two-dimensional arrays of circular dots with 200 nm diameter and 500 nm period were made by interferometric lithography and ion beam etching. Large area patterning (about 1 cm2) allows integral magnetic measurements with an alternating gradient magnetometer. The magnetic behavior of thick patterned films is dominated by the demagnetizing field. Ultrathin continuous films and dot arrays of these show a strong uniaxial in-plane magnetic anisotropy with the easy axis in [110] direction which is fully conserved during the patterning process. This means that two stable remanent single domain states exist in ultrathin Fe(001) sub-μm dots on GaAs(001) because (i) the magnetostatic energy is not important due to the small aspect ratio, and (ii) the Fe/GaAs(001) interface creates a strong uniaxial in-plane magnetic anisotropy. Nanomagnets with these properties seem very attractive for high density memory elements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that determined reversal processes in terbium/iron multilayer films. Information on the form of hysteresis; Remanence measurements; Evaluation of fluctuation fields and activation volumes for the series of films.

Investigates the magnetic microstructure of an amorphous GdFe system with a pronounced perpendicular magnetic anisotropy. Measurement of the size distributions and correlations lengths in the nanometer range of magnetic precipitates in granular systems; Information on the electronic structure of the system; Examination of magnetic scattering curves obtained; Experimental procedures used; Results of the study.

The spin accumulation in a n-GaAs channel produced by spin extraction into a (Ga,Mn)As contact is measured by cross-sectional imaging of the spin polarization in GaAs. The spin polarization is observed in a 1 μm thick n-GaAs channel with the maximum polarization near the contact edge opposite to the maximum current density. The one-dimensional model of electron drift and spin diffusion, frequently used, cannot explain this observation. It also leads to incorrect spin lifetimes from Hanle curves with a strong bias and distance dependence. Numerical simulations based on a two-dimensional drift-diffusion model, however, reproduce the observed spin distribution quite well and lead to realistic spin lifetimes. [ABSTRACT FROM AUTHOR]

Recent discoveries of phenomena that relate electronic transport in solids to the spin angular momentum of the electrons are the fundamentals of spin electronics (spintronics). The first proposed conceptual spintronic device, the spin field-effect transistor—which has not yet been successfully implemented—requires the creation and detection of spin-polarized currents in a semiconductor. Whereas electrical spin injection from a ferromagnetic metal into GaAs has been achieved recently, the detection techniques used up to now have drawbacks like the requirement of large magnetic fields or limited information about the spin polarization in the semiconductor. Here we introduce a method that, by observation across a cleaved edge, enables us to directly visualize fully remanent electrical spin injection into bulk GaAs from a ferromagnetic contact, to image the spin-density distribution in the semiconductor in a cross-sectional view and to separate the effects of spin diffusion and electron drift. [ABSTRACT FROM AUTHOR]

X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution down to 25 nm were used to image out-of-plane magnetized (4 ÅFe / 4 ÅGd)×75 systems. Magnetic domains could be studied in arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nmCr / 50 nmFe / 6 nmCr film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II. [ABSTRACT FROM AUTHOR]

Introduces a scheme for ultrafast generation of local magnetic fields in hybrid ferromagnetic semiconductor structures. Procedures involved; Optical pumping of a Schottky-barrier diode; Advantages and drawbacks of the method.

We investigate submicron ferromagnetic PdNi thin-film strips intended as contact electrodes for carbon nanotube-based spintronic devices. The magnetic anisotropy and micromagnetic structure are measured as function of temperature. Contrary to the expectation from shape anisotropy, magnetic hysteresis measurements of Pd0.3Ni0.7 on arrays containing strips of various width point towards a magnetically easy axis in the sample plane, but transversal to the strip direction. Anisotropic magnetoresistance measured on individual Pd0.3Ni0.7 contact strips and magnetic force microscopy images substantiate that conclusion. [ABSTRACT FROM AUTHOR]

The authors investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions. The tunneling magnetoresistance (TMR) effect was probed for different types of Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is increased and is observable at room temperature. If an epitaxial Fe/GaAs(001) interface is involved, the tunnel junction exhibits a bias dependent inversion of the TMR effect. This is a first experimental signature for band structure effects at an Fe/GaAs interface and is relevant for spin injection experiments. [ABSTRACT FROM AUTHOR]

Spin injection from Fe(001) and (Ga,Mn)As(001) into n-GaAs(001) was investigated using a method which provides two-dimensional cross-sectional images of the spin polarization in GaAs. While the distribution of the spin polarization below the injecting contact is nearly uniform for (Ga,Mn)As, a strong confinement near the contact edge is observed for Fe and FeCo. The spin polarization in GaAs changes sign when the injected current is reversed. Multiple sign reversals as a function of bias voltage as reported previously for Fe injectors are not observed with (Ga,Mn)As and Fe contacts grown on clean n++-GaAs in agreement with earlier results for an epitaxial FeCo injector. [ABSTRACT FROM AUTHOR]

The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb[sub 25](Fe[sub 75]Co[sub 25])[sub 75] layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]