Search

Fe/MgO/Fe single-crystalline magnetotunneling structures were epitaxially grown on GaAs(001). An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. Such Fe/Cr/Fe/MgO/Fe/GaAs(001) structures exhibit in-plane anisotropy, which ensures a discrete switching behavior of magnetization simplifying the shape of the hysteresis loop. The field dependence of magnetization was measured along the [110] and [100] crystallographic directions of GaAs(001) substrate and modeled by minimizing the total magnetic energy of the system. A peculiar magneto-optical behavior (similar to a reversed hysteresis loop) is explained by magneto-optical phase angles, which are determined mainly by the optical properties of the semiconducting GaAs substrate. [ABSTRACT FROM AUTHOR]

We have performed magnetic domain imaging with spatial, temporal, and layer resolution using x-ray photoelectron emission microscopy. The element selectivity of x-ray magnetic circular dichroism allows the magnetization dynamics of the different magnetic layers in spin-valve-like FeNi/Cu/Co trilayers to be studied separately, using the time structure of synchrotron radiation. The unique possibilities of this technique have been used to study the influence of the intrinsic magnetic properties of the different layers on the magnetization dynamics and the interlayer magnetic coupling. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Fe/Cr/Fe trilayers were epitaxially grown on atomically flat GaAs(001). For the thickness of Cr spacer layer corresponding to antiferromagnetic coupling, “reversed” minor hysteresis loops were measured with longitudinal magneto-optical Kerr effect (MOKE), i.e., a negative “magnetization” signal was detected when the thicker bottom Fe layer was saturated along the applied field. This behavior is interpreted by depth variations of the MOKE sensitivity. Magnetization reversal shows that both antiferromagnetic switching and spin–flop transition fields depend on the ratio of both Fe film thicknesses. The shape of the MOKE loops becomes more complex with further deposition of MgO and Fe layers on the top of the Fe/Cr/F/GaAs(001) stack. Superconducting quantum interference device measurements confirm the interpretation of the MOKE loops and demonstrate homogeneity and sharpness of the interfaces in the structures. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Tetragonal distortion in Fe0.5Co0.5 alloy films grown epitaxially on Rh(001) substrates results in an easy magnetization axis perpendicular to the film plane up to the thickness of 17 ML. The distortion is supported by a Rh-overlayer; thus the strong perpendicular anisotropy can be kept when another Fe0.5Co0.5 film is grown on top of the Rh/Fe0.5Co0.5/Rh(001) structure. Depending on the thickness of the Rh spacer, the top and bottom Fe0.5Co0.5 films are either ferro- or antiferromagnetically coupled. The net magnetization of the antiferromagnetically coupled Fe0.5Co0.5/Rh/Fe0.5Co0.5 bilayer switches at the field which depends on the difference between magnetizations of both the Fe0.5Co0.5 layers. The final covering of the Fe0.5Co0.5/Rh/Fe0.5Co0.5/Rh(001) structure with Rh increases the switching field. The effect is explained by a locally enhanced magnetization in the Rh/Fe1-xCox interfaces. [ABSTRACT FROM AUTHOR]

Fe/MgO/Fe/Cr/Fe tunneling structures were epitaxially grown directly on GaAs(001) without buffer layer. Interdiffusion in the Fe/GaAs interface was investigated using conversion electron Mössbauer spectroscopy. An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. For transport measurements, optical lithography and ion etching were applied to reduce the junction area. A tunneling magnetoresistance of 10%–12% at room temperature was found. [ABSTRACT FROM AUTHOR]

Magnetization as a function of temperature calculated with Monte Carlo techniques is compared to experimental results of Fe stripes grown on vicinal Cu(111) surfaces. The stripes are step decorations grown with molecular beam epitaxy (MBE), are 1-2 monolayers thick, and display perpendicular magnetization. The atomic parameters are determined from fully relativistic electronic structure calculations. The moments are found to be 2.57&micron;[sub B], with some variation due to film thickness, and uniaxial anisotropy of 40 &micron;Ry/atom for Fe atoms facing vacuum. The Heisenberg model extended to include crystalline anisotropy as well as dipole-dipole interactions is considered for two different values of the exchange constant: J=20 and 2 meV. Under a large applied field (4000 G), the calculated saturation magnetization falls slowly from 507 emu/cm[sup 3] with an increase in temperature until it falls rapidly around 600 K, after which a more modest falloff with an increase in temperature is observed. For larger d the rapid change occurs for higher temperatures. The importance of disorder in the height and width of the stripes is investigated by generating stripe geometries with a model that incorporates nucleation and growth of Fe particles at step edges under the constraint of constant deposition from MBE. The primary effect of disorder in the stripes is to reduce the saturated magnetization at lower temperatures. [ABSTRACT FROM AUTHOR]

We present static measurements of the domain structure and dynamic results on domain wall motion and local susceptibility obtained by spin-polarized scanning tunneling microscopy. The topography and the magnetic structure of the sample are recorded simultaneously with down to 10 nm resolution. With this technique, domain wall movement on Co(0001) is studied in situ. In some cases, the magnetization of the sample is locally influenced by the stray field of the tip. Measuring higher harmonics in the tunneling current allows one to quantify this influence and measure magnetic susceptibilities on similar scales. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on Fe films grown on Au-buffered Si(001) showing perpendicular magnetization at ambient temperatures. The in-plane magnetization in ultra-thin Fe films grown at 150 K reorients irreversibly out-of-plane as a result of annealing close to room temperature. A Au cap layer which is expected to segregate to the top of the Fe film may be responsible for this behaviour. This hypothesis is based on the observation of an in-plane to out-of-plane reorientation of magnetization upon the growth of an ultra-thin Au cap layer on a slightly thicker Fe film. The origin of such a strong out-of-plane anisotropy of Fe induced by Au is discussed. [ABSTRACT FROM AUTHOR]

The article focuses on the X-ray magnetic circular dichroism (XMCD) imaging with the use of photoelectron emission microscopy (PEEM) in layer-resolved magnetic domain. It discusses magnetization vector of every domain and its imaging, and the images in layer-resolved magnetic domain imaging. It mentions that XMCD-PEEM imaging for layer-resolved magnetic domain is a good tool for research on magnetic interlayer coupling.

The scenario of the magnetization reorientation in second-order perpendicular anisotropy approximation is theoretically studied by means of Monte-Carlo simulations. The microstructure is investigated as a function of the difference between first-order anisotropy and demagnetizing energy K[sub eff]=K[sub 1]-E[sub D] and the second-order anisotropy K[sub 2]. An influence of the second-order perpendicular anisotropy on the spin reorientation transition is found when K[sub eff] vanishes. The broadening and coalescing of domain walls found earlier for K[sub 2]=0 is prevented by positive K[sub 2]. The domain wall width and energy are determined by K[sub 2]. For K[sub 2]>0 the transition via a canted vortex-like structure is found which yields the smooth, continuous connection between the vertical domain structure and the vortex structure with in-plane magnetization. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on magnetic and magnetotransport properties of single-crystalline Co2 MnSi films grown by using conventional pulsed laser deposition (PLD) method on moderately heated semiconductor GaAs(001) substrates. The films exhibit the expected high Curie temperature and a strong in-plane uniaxial magnetic anisotropy with the easy axis of magnetization along the [1-10] direction. A saturation magnetization of 950 emu/cm³ was measured at 5 K. The temperature dependence of the resistivity shows metallic behavior down to low temperatures. At 5 K, a rather large negative magnetoresistance (MR) of 1.26% has also been observed. [ABSTRACT FROM AUTHOR]

The magnetization reversal dynamics of an Fe20Ni80/Cu/Co spin valve is investigated on the nanosecond time scale by magnetic microscopy with time and layer resolution. It is found that the speed by which micron-sized magnetic domains in the magnetically soft Fe20Ni80 layer are expanded by external field pulses exhibits a dependence on the change in domain-wall length, and on the coupling to the local magnetization direction of the Co layer. [ABSTRACT FROM AUTHOR]

Selective adsorption of Fe deposited on the organic molecule 3,4,9,10-perylene-tetracarboxylic-3, 4,9,10-dianhydride (PTCDA) is used to prepare a self assembled magnetic nanostripe structure on a vicinal Ag surface. Scanning tunneling microscopy reveals that after PTCDA deposition on the Ag(10 8 7) surface a grating-like domain pattern is formed. It consists of alternating stripes of molecule-covered facets and uncovered (111) terraces. Fe adsorption takes place selectively on the molecule-covered stripes forming disk-shaped super-paramagnetic islands with a polar easy magnetization axis. [ABSTRACT FROM AUTHOR]

Magnetization configuration in Fe/Rh/Fe0.5Co0.5/Rh(001) can be non-orthogonal due to competition between the anisotropy and the exchange coupling. Soft x-ray resonant magnetic reflectivity allows us to probe the magnetic profile along the growth axis with in-plane and perpendicular magnetization components. By using different modes of acquisition, we show that it is possible to determine separately the magnetic profile of both magnetization components. Measurements at the Co L3-edge enable us to investigate the magnetism of the alloy layer independently from the layer of Fe. [ABSTRACT FROM AUTHOR]

We present a spin-polarized scanning tunneling microscope (Sp–STM) for imaging the magnetic in-plane component of magnetic surfaces. Magnetic in-plane sensitivity is obtained by using a ferromagnetic ring as a Sp–STM tip. By periodically switching the magnetization of the ring, the spin-dependent tunneling current between the ring and a spin-polarized sample is measured. The topography and the spin polarization can be imaged at the same time. We resolved the 180° domain wall of Fe whiskers and antiferromagnetic coupled Mn layers on Fe(001). © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a technique for the measurement of film stress, magnetization, and magnetoelastic coupling. Properties of optical deflection; Measurement of magnetic moments; Description of the novel magnetoelastic coupling behavior.

The magnetism of sesquilayer bcc iron films on W(110) is investigated. Coercivity data and theoretical calculations indicate that the freezing of the magnetization at low temperatures reflects exchange-dominated domain-wall pinning rather than superparamagnetic spin-glass behaviour. [ABSTRACT FROM PUBLISHER]

The expansion of magnetic domains in thin films with perpendicular anisotropy is investigated. To determine the domain-wall-velocity as a function of the applied magnetic field a selfconsistent magnetic-viscosity approach is used. The main predictions of the theory are a linear behaviour in the moderately strong fields, a quasi-exponential behaviour for fields close to the propagation field, and a negative velocity for very small and negative fields. The predictions of the theory are compatible with domain-wall investigations on Au/Co/Au sandwiches. [ABSTRACT FROM PUBLISHER]

Studies the influence of adsorbates on surface magnetization and Stoner excitations of nickel. Spectroscopic technique used in the study.

An optical 2-beam surface stress measurement and magneto-optical Kerr-effect has been combined with a liquid helium cooled cryostat. Sample temperatures down to 30 K and magnetic fields up to 0.7 T are achieved under UHV conditions. Low temperatures are exploited to obtain the first experimental data on the surface stress change induced by the adsorption of the noble gas Xe on Pt(111). High magnetic fields and low temperatures are used to characterize the magnetic properties of Co monolayers in longitudinal and polar Kerr geometries. The effective magnetic anisotropy is extracted from hard axis magnetization loops. [ABSTRACT FROM AUTHOR]

Abstract: Numerical micromagnetic simulations are performed to study the magnetic configurations of ultrathin films with spatially varying magnetic anisotropy. Investigating infinitely long stripes with alternating in-plane/out-of-plane uniaxial anisotropy we find states of uniform, canted and alternating magnetization as function of the width of the stripes. A simple analytical model is given to describe the canting by means of a fourth order anisotropy term that is caused solely by the microstructure. Furthermore, the system is described macroscopically by averaging the magnetization of the various states. In this framework the spin reorientation transition between states of uniform magnetization is studied as a function of the stripes density. We find that the rotation of the average magnetization takes place always continuously and is sharper for a higher density of stripes. [Copyright &y& Elsevier]

The continuum theory of micromagnetism is used to study ultrathin films with magnetic anisotropy varying laterally on the nanometer scale. A series of infinitely long stripes with alternating in- and out-of-plane uniaxial anisotropy is considered as a model for patterned ferromagnetic films. The analytical solution based on an effective anisotropy description of the dipolar energy is given as a function of the material parameters (exchange and anisotropy constants) and the width of the stripes. States of uniform and non-uniform magnetization are obtained. For film of finite thickness the exact value of the dipolar energy is calculated numerically and the numerical solution is compared with the analytical one. We find that the correction to the dipolar energy is negligible for nickel, while for cobalt and iron it has to be considered as a function of the anisotropies, the width of the stripes and the thickness of the film. [Copyright &y& Elsevier]

The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated by means of a scanning electron microscope with polarization analysis. In particular, the influence of a magnetic field on the domain structure has been studied. Here, we concentrate on squares of different size (3–30 μm) and variable thickness, although triangles and bars with aspect ratios up to 1:30 have been studied, too. In the as-grown state the microstructures with an edge length larger than 3 μm exhibit a multidomain structure, while the smaller ones are always single domain. After saturating the structures by a strong field, the magnetization can be switched homogeneously by either ±90° or 180° independent of size and shape. The microstructures remain in a single-domain state. Roughly 20% of the ultrathin particles show a two-step 180°-switching via a 90°-state. An analytical model is developed yielding coercivities of the right order of magnitude. The two-step reversal process can be explained in the framework of this model. [Copyright &y& Elsevier]

We investigate the depth dependence of the canted magnetization in a bcc Fe ultrathin film grown on a vicinal Ag substrate. This study is performed for different Fe thicknesses, in the vicinity of the spin reorientation transition, by soft x-ray resonant magnetic reflectivity (SXRMR). Above 5.5 monolayers, the high spatial resolution of SXRMR allows us to describe a gradient of the canted magnetization. The tilt angle is larger near the Ag interface and decreases towards the surface. This noncollinearity is ascribed to a different balance of various anisotropies across the layer thickness. Below that value, a large increase of the tilt angle is observed and ascribed to the spin reorientation transition. Unlike the previous situation, the tilt angle is found to be homogeneous throughout the film. This can be related either to the out-of-plane spin reorientation associated to a reduced number of monolayers or to the q-space limitation of the SXRMR technique at the Fe L3 edge. [ABSTRACT FROM AUTHOR]

Using soft-x-ray magnetic resonant reflectivity measurements, we have studied the layer-resolved temperature dependence of the magnetic structure in a six-monolayer-thick fcc-Fe film grown on Cu(OOl) by pulsed laser deposition. Temperature-dependent reflectivity curves were fitted on the basis of the Heisenberg Hamiltonian involving only a small number of temperature-independent interlayer and intralayer exchange interaction parameters. Our study supports the model of the formation of the blocks of layers with robust magnetic structure whereas the interblock interactions are relatively weak. The temperature-dependent magnetization profile derived on the basis of the exchange interaction parameters reveals a strong inhomogeneity within the film, which is in agreement with the recent theoretical prediction. [ABSTRACT FROM AUTHOR]

We investigate the magnetization reversal of individual Co islands on Cu(111) in the size range of N = 700 to 18 000 atoms by spin-polarized scanning tunneling microscopy at 8 K. The switching field Hsw changes with island size in a nonmonotonic manner: it increases with island size and reaches a maximum value of 2.4 T at N = 5500 atoms, and it decreases for larger islands. We extract the energy barrier for magnetization reversal as a function of island size. The maximum Hsw, corresponds to an energy barrier of 1 eV. Our results elucidate a crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation with increasing size at around 7500 atoms. [ABSTRACT FROM AUTHOR]

Abstract: So-called split hysteresis loops have been measured for ultrathin ferromagnetic films grown on stepped surfaces. Since the shape of the loops is sensitive to the direction in which the magnetic field is applied with respect to the steps, the sample orientation against the field is particularly important. We performed systematic magneto-optical Kerr effect studies for 15 and 58ML of Fe grown on Au(1,1,13). In view of the complex magnetic anisotropy of such systems we discuss representative hysteresis loops taken at sample orientations misaligned from the field (and laser beam) direction. In particular, the presence of a so-called low field component to the hysteresis loops is discussed and its reversed polarity is explained. [Copyright &y& Elsevier]

Abstract: A contribution originating from the Co/Pd and Fe/Pd interfaces to the magneto-optical Kerr effect (MOKE) rotation is analyzed for Co and/or Fe films grown on a Pd-buffer-monolayer on Cu(001). A clear increase of the MOKE signal in comparison to the Co(Fe) films grown directly on Cu(001) is detected. An interpretation is supported by similar observations for Co films grown on Pd(110) and Pd(001). In particular, the sign reversal of the Kerr loops with increasing thickness of the Co(Fe) films is discussed. Magneto-optical effects are separated from the real magnetization and its dependence on the film thickness. [Copyright &y& Elsevier]

Single-crystalline (Fe/Cr/Fe)AFM/Cr/Fe structures were epitaxially grown on atomically flat GaAs(0 0 1). Choosing the same thickness of the antiferromagnetically (AFM) coupled Fe layers in the bottom (Fe/Cr/Fe)AFM structure, their net magnetization is balanced to zero, in particular up to a spin–flop transition when the field is applied along the [1 1 0] direction. For the Cr thicknesses at which the top Fe layer is weakly magnetically coupled to the bottom (Fe/Cr/Fe)AFM structure, at low fields, the magneto-optical Kerr effect and/or SQUID signal from the sample corresponds to the top Fe layer only. An influence of the Cr spin structure on the magnetization reversal in the Fe layer is reported. In particular, a strong increase of coercivity (by a factor of 12) is found at low temperatures. A 90° coupling is detected which affects the minor loops measured along the [−1 1 0] and [1 0 0] directions. [Copyright &y& Elsevier]

We report on the out-of-plane magnetization in Fe/Ni and Fe/Au bilayers grown on GaAs(0 0 1). For Ni thicknesses of several monolayers, the magnetization of the Fe/Ni bilayer increases linearly with the Fe film thickness, which is typically observed when Fe grows in the BCC-structure. For thicknesses up to 8 ML, Ni is nonmagnetic such as in the Fe/Ni/GaAs(0 0 1) structure. This could be due diffusion of Ga. Up to thickness of 2 ML the Fe overlayer is magnetized out-of-plane, however at low temperatures only. The nature of the out-of-plane spin orientation is discussed, also in view of the crystallographic structure of the Fe/Ni bilayer and by comparison with the Fe/Au bilayer grown on GaAs(0 0 1). [Copyright &y& Elsevier]

By using a photoemission electron microscope in combination with X-ray magnetic circular dichroism, the domain configuration in a single crystalline Co film exchange coupled to an Fe50Mn50 film is obtained. The effect of the ferromagnetic/antiferromagnetic interaction is observed to be different in Co domains with different magnetization direction, establishing the fact that the exchange bias is locally set by the magnetization of the ferromagnetic layer, without external field. [Copyright &y& Elsevier]

The evolution of the domain structure with the thickness of bcc Fe films deposited on the Ag(116) vicinal surface is studied by spin-polarized low-energy electron microscopy. We show that a spin reorientation transition proceeds via two mechanisms: continuous rotation of magnetization within the vertical plane perpendicular to the steps and discontinuous reorientation of the in-plane component of magnetization, leading to splitting of the domains. In contrast to previously investigated systems with stripe domains, we reveal that in the case of a vicinal ferromagnetic surface, the domain width increases while changing the orientation of the magnetization from a canted out-of-plane state into an in-plane state. A theoretical model developed in this work successfully describes the domain structure behavior observed in our experiments and can be equally applied to other ferromagnetic films grown on vicinal surfaces. [ABSTRACT FROM AUTHOR]