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Focused ion beam (FIB) irradiation was applied to an ultrathin Pt/Co/Pt film to create micrometer-sized, square-shaped regions with perpendicular orientation of magnetization embedded in an in-plane magnetized environment. The FIB parameters like ion fluence and scanning direction are used to control the magnetic properties of the irradiated areas. We have studied the magnetic and magnetooptical properties in the irradiated areas as a function of ion fluence by means of component selective magnetooptical Kerr microscopy that measures separately pure polar and pure longitudinal components of magnetization. Two fluence ranges that induce perpendicular magnetization components were observed. In the higher fluence range, four regions with independently inclined out-of-plane magnetization, depending on FIB fast scan direction, and an unexpected magnetic domain structure were distinguished inside the squares irradiated by FIB.

Magneto-optical microscopy, prominently represented by Kerr microscopy, is the most versatile in-lab imaging technique for magnetic microstructure analysis on any kind of magnetic material being microscopically ordered in magnetic domains. Domains can be studied on a wide range of lateral scales reaching from centimetres down to 200 nanometres, under static conditions as well as under dynamic magnetic field excitation ranging between quasistatic and beyond the microwave regime, at temperatures between 4 K and 800 K, and in applied fields exceeding the Tesla range in arbitrary directions. The surface magnetisation vector field of soft magnetic materials can be quantitatively measured, and the magnetic layers in superlattices may be imaged separately. By plotting the image intensity as a function of magnetic field, local magnetisation curves are obtained that can be interpreted straightforwardly as the underlying magnetisation process is imaged simultaneously. In this chapter the physical and technical basics of magneto-optical microscopy are reviewed together with examples that demonstrate the benefits of the technique.

We report on the direct observation of spin wave and elastic wave emission from magnetic domain walls in ferromagnetic thin films. Driven by alternating homogeneous magnetic fields the magnetic domain walls act as coherent magnetisation wave sources. Directional and low damped elastic waves below and above the ferromagnetic resonance are excited. The wave vector of the magnetoelastically induced acoustic waves is tuned by varying the excitation frequency. The occurrence of elastic wave emission is proved by a combination of micromagnetic and mechanical finite element simulations. Domain wall emitted magnetostatic surface spin waves occur at higher frequencies, which characteristics are confirmed by micromagnetic simulations. The distinct modes of magnetisation wave excitation from micromagnetic objects are a general physical phenomenon relevant for dynamic magnetisation processes in structured magnetic films. Magnetic domain walls can act as reconfigurable antennas for spin wave and elastic wave generation. The wave orientation can be controlled separately via the domain wall orientation for elastic waves and via magnetization orientation for magnetostatic surface spin waves.

We report on a component-selective and vectorial magneto-optical imaging setup for the visualization of magnetization processes with picosecond temporal resolution. The stable imaging setup is suitable for the investigation of high excitation frequency magnetization dynamics, including domain wall motion, precession of magnetization, and spin-waves. The orthogonally aligned in-plane and out-of-plane components of magnetization are separated by untangling the superpositioned longitudinal and polar magneto-optical effects. Combining images obtained with varying plane and angle of incidence of illumination allow for the quantitative and time-dependent extraction of the spatial magnetization response. The capabilities of the setup are demonstrated with the phase-locked imaging of spin precession and spin-waves in a structured Co 40 Fe 40 B 20 thin film at the precessional frequency of the magnetic microstructure at 1.9 GHz.

Fabrication of a multistrip magnetic/nonmagnetic structure in a thin sandwiched Ni layer [Si(5 nm)/Ni(10 nm)/Si] by a focused ion beam (FIB) irradiation has been attempted. A control experiment was initially performed by irradiation with a standard 30 keV Ga ion beam at various fluences. Analyses were carried out by Rutherford backscattering spectrometry, X-ray reflectivity, magnetooptical Kerr effect (MOKE) measurements and MOKE microscopy. With increasing ion fluence, the coercivity as well as Kerr rotation decreases. A threshold ion fluence has been identified, where ferromagnetism of the Ni layer is lost at room temperature and due to Si incorporation into the Ni layer, a Ni0.68Si0.32 alloy layer is formed. This fluence was used in FIB irradiation of parallel 50 nm wide stripes, leaving 1 micrometer wide unirradiated stripes in between. MOKE microscopy on this FIB-patterned sample has revealed interacting magnetic domains across several stripes. Considering shape anisotropy effects, which would favor an alignment of magnetization parallel to the stripe axis, the opposite behavior is observed. Magneto-elastic effects introducing a stress-induced anisotropy component oriented perpendicular to the stripe axis are the most plausible explanation for the observed behavior., 12 pages, 12 figures (Figure numbers up to 7)

Highlights X-ray irradiation of amorphous stripes allows to stabilize a transverse 180o wall. An inhomogeneous resonance can be excited with a 180° phase-shift across the wall. That phase-shift can be exploited into the design of magnonic devices. We report on the induction, through X-ray irradiation, of local anisotropy modifications in amorphous Fe80B20 stripes prepared by laser lithography from 15 nm thick films deposited by pulsed laser ablation. Those anisotropy modifications, taking place in a zone having a dimension of 15 μm around the X-ray beam (2 µm width) incidence area center point, lead to an effective transverse-to-the-stripe long axis local magnetic easy axis that can be exploited to stably localize a 180° domain wall, in remanence after saturation with a transverse-to the stripe easy axis dc field. Upon stabilizing that wall it is possible to excite spatially inhomogeneous ferromagnetic resonances nearby the irradiated region (IR). The time dependencies of the magnetization precession at both sides of the IR exhibit a uniform phase shift of 180° over distances of the order of 20 μm from the stabilized domain wall. This work has been developed with funds corresponding to project MAT2016-80394-R financed by the Spanish Research Agency (AEI). We also acknowledge the Spanish Ministerio de Ciencia e Innovaci ' on and Consejo Superior de Investigaciones Cientificas for financial support and for provision of synchrotron radiation at beamline BM25-SpLine (ESRF). This research used resources of the Advanced Light Source, a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. FC and JMG would like to dedicate this work to the memory of Dr. Dominique Givord with gratitude for the many things they were able to learn from him Peerreview

Magnetic properties of highly magnetostrictive amorphous glass-coated microwires are strongly correlated to the presence of a glass coating that introduces a spatially inhomogeneous stress field distribution. We investigate the influence of mechanical stresses on the inclination of magnetic domain walls in magnetic microwires. Magneto-optical Kerr effect imaging is used to compare the tilted orientation of the domain wall shape in as-cast and annealed microwires. Angular dependencies of magnetization loops measured by alternating gradient field magnetometry reveal that the change of domain wall tilting with annealing is related to the decrease of magnetic anisotropy with axial orientation. Finally, micromagnetic simulations are used to show that sufficiently high uniaxial magnetic anisotropy gives rise to the presence of observed charged domain walls with tilted orientation.

We report the structural properties of thin magnetic Permalloy films treated by two different methods: broad beam Ga+ ion implantation at an energy of 30 keV as well as annealing at different temperatures under ultrahigh vacuum. Transmission electron microscopy imaging and X-ray diffraction measurements have demonstrated that both ion implantation and annealing (above 300 °C) lead to further material crystallization and crystallite growth. Whereas annealing (above 400 °C) leads to a strain-free state with an almost constant lattice parameter and to a further enhancement of the initial (111) texture, ion beam implantation boosts the growth of small, arbitrarily oriented crystallites and leads to an linear increase in the lattice parameter, introducing microstrain into the sample. The observed decrease in the saturation magnetization for the implanted samples is mainly attributed to the presence of the non-magnetic Ga atoms incorporated in the Permalloy film itself. The increase in the saturation magnetization for the samples annealed at temperatures above 500 °C is explained by an arising dewetting effect since no ordered Ni3Fe phase was detected with anomalous X-ray diffraction.

The microscopic processes underlying magnetostriction in ferrites were studied for the case of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ single crystals by high-resolution in situ x-ray diffraction and complementary magnetic microscopy techniques. The data support the reports of Yang and Ren [Phys. Rev. B 77, 014407 (2008)] that magnetostriction in these materials originates from the switching of crystallographic domains, similar to ferroelastic or ferroelectric domain switching, and reveals the presence of two coexisting tetragonal spinel structures, corresponding to domains of high and of low strain. The latter alternate in the crystal, separated by 90\ifmmode^\circ\else\textdegree\fi{} domain boundaries, and can be explained by the effect of internal stress emerging during the transition into the ferrimagnetic phase. During magnetization of the sample two structural transitions are observed: a conversion of the transversal into axial domains at 1.95 kOe and a growth of the high-strain domains at the cost of the low-strain axial domains at 2.8 kOe. These microscopic changes are in good agreement with the macroscopic magnetization and magnetostriction behavior of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$.

High density magnetic domain wall gratings are imprinted in ferromagnetic-antiferromagnetic thin films by local ion irradiation by which alternating head-to-tail-to-head-to-tail and head-to-head-to-tail-to-tail spatially overlapping domain wall networks are formed. Unique magnetic domain processes result from the interaction of anchored domain walls. Non-linear magnetization response is introduced by the laterally distributed magnetic anisotropy phases. The locally varying magnetic charge distribution gives rise to localized and guided magnetization spin-wave modes directly constrained by the narrow domain wall cores. The exchange coupled multiphase material structure leads to unprecedented static and locally modified dynamic magnetic material properties.

The dynamic magnetic properties of soft-ferromagnetic thin film element arrays are strongly influenced by long range interelement magnetostatic interaction. In order to estimate the effective array dipolar field a quantitative model is presented, which is based on the superposition of stray fields that arise from the neighborhood of a reference element. Kittel's equation, that describes the magnetodynamics, is generalized for magnetically saturated arrays by additional array dipolar field terms. Measurements of the magnetodynamic response of quasi-saturated arrays with a rectangular base agree with theoretical predictions. Thus, our model allows the estimation of the frequency of the uniform precessional mode in mesoscopic thin film arrays with non-negligible magnetostatic interaction.

The influence of homogeneous magnetic fields with flux density up to 1 T superimposed during the deposition of CoFe thin films on their properties has been studied. It has been clearly demonstrated that the superimposition of magnetic fields influences the resulting layer properties significantly. A pronounced impact on the layer morphology has been observed. The layers deposited under the influence of the parallel-to-electrode magnetic field appear denser and more homogenous than those obtained without a magnetic field. On the contrary, the layers deposited in the perpendicular-to-electrode magnetic field appeared more diverse. A scaling analysis revealed a smoothing effect of a parallel- and a roughening effect of a perpendicular-to-electrode magnetic field. No influence of magnetic fields neither on the deposited layers chemical composition nor the structure and texture has been found, whereas the internal stress state of the layer is affected by the superimposition. The effects are discussed with respect to the Lorentz force driven convection, which increases the electrochemical reaction's rates and improves desorption of hydrogen from the electrode surface. The alterations of magnetic properties of the CoFe thin films correlate well with the observed microstructural changes. Moreover, an in-plane magnetic anisotropy is induced by a parallel magnetic field superimposition. This phenomenon origins from a preferential next neighbour atomic pair-ordering in the direction of the magnetic field, e.g. magnetization, during deposition of the ferromagnetic alloy.

A model is presented that semi-quantitatively describes the dependence of precessional frequency on magnetic domain width in ferromagnetic thin film elements. With decreasing domain width an increase of precessional frequency at zero-bias field by a factor of about 1.5 is found experimentally and from the calculations. The modelled value of change of precessional frequency is in agreement with the experimental results. The simple model offers the opportunity to relate the drastic effects of domain structure on the dynamic magnetic properties of soft-magnetic thin films by a straightforward approach.

We investigated the high-frequency modes of 40 mum wide, 160 nm thick Fe 70Co8B12Si10 squares using time-resolved scanning Kerr microscopy. Two modes were identified using pulsed field excitation while the spatial character of the out-of-plane and in-plane magnetization component was investigated using harmonic field excitation. The field dependence of the two modes has been fitted using the Damon-Eshbach model.

We used polarized neutron reflectometry for a quantitative study of the field dependent arrangement of the magnetization vector in the different regions of an ion beam imprinted stripe pattern in a magnetic film. For the magnetic patterning of the Co70Fe30 film we took advantage of the exchange bias to an antiferromagnetic Mn83Ir17 layer which was changed locally by He-ion bombardment. The exchange bias was set to be antiparallel in the two different striped regions. We found that after magnetization reversal of half of the stripes the magnetization in neighbouring regions is periodically canted with respect to the stripe axis so that the net magnetization of the ferromagnetic film tums almost perpendicular to the stripes. At the same time the projection of the magnetization vector onto the stripe axis has a periodically alternating sign. (c) 2007 Published by Elsevier Ltd

The correlation between dynamic magnetic domain formation and dynamic magnetization loss is studied in nanocrystalline FeCuNbSiB tape wound cores with different strengths of transverse field-induced anisotropy. A significant excess loss component is measured, in particular for high induction levels. The excess loss cannot be explained by homogeneous magnetization rotation, the ideal magnetization process for a transverse field-induced anisotropy. In fact, dynamic domain observation reveals inhomogeneous rotation of magnetization, wall displacement processes, and domain nucleation besides homogeneous rotation. Domain refinement is accordingly observed with increasing frequency. The domain width is smallest for cores with weak induced anisotropy, where excess loss is the lowest. In these cores, surface roughness yields residual domains, which persist at field strengths above the inductively measured saturation field.

Hysteresis loops were calculated for a model with ferromagnetic grains spin-flop coupled to interacting antiferromagnetic grains with randomly distributed easy axes. The interface between these two layers is assumed to be fully compensated. Field cooling simulated by a Monte-Carlo algorithm and subsequent calculation of the hystersis loop reveals asymmetries in the ascending and descending part of the hysteresis loop, respectively. On the descending branch a steep change of the magnetization can be observed. On the ascending branch homogeneous rotations of the magnetization cause a smoother change of the magnetization. The strong asymmetries vanish after a few hysteresis loop calculations.

A periodic magnetic stripe array has been studied with a combination of real and reciprocal space methods: Kerr microscopy and polarized neutron reflectivity. The basic features of our experimental neutron data are well reproduced by a theoretical model using the distorted Born wave approximation and providing a set of parameters quantifying the magnetization arrangement in the stripe array system. While the specular neutron reflectivity measures a mean value of the optical potential averaged over a number of structural elements within the neutron coherence length, Bragg diffraction filters out magnetic correlation effects in the system of individual magnetic units within this length scale. Off-specular diffuse scattering probes correlations of magnetization fluctuations on a scale smaller than the coherence length. This altogether gives access to a detailed understanding of the magnetization arrangement which appears to be quite complex and hardly accessible by other methods.

The magnetization reversal process in the ferromagnetic layer of an exchange-biased Co90Fe10(20 nm)/Ir23Mn77(10 nm) film structure, deposited by dc-magnetron sputtering, is imaged by high-resolution Kerr microscopy. Additionally, high-resolution magnetization loops are measured by deriving the magnetization signal from the average image intensity. The magnetization reversal occurs first by magnetization rotation under the development of ripple-like structures. The modulated structures then partially switch, generating complicated multidomain configurations, which finally annihilate by large angle domain wall movement. The amount of magnetization rotation at different field directions is quantified by measuring the transversal magnetization components during reversal. A strong asymmetry, both in domain behavior and magnetization loop, between the forward and recoil branch of the magnetization reversal is found. The magnitude of asymmetry strongly depends on small angle misalignments between the direction o...

Time-resolved wide-field magneto-optical microscopy with picosecond time resolution and with phase-locked harmonic excitation is used to image the fundamental dynamic modes of magnetic domain and domain-wall states in soft-magnetic thick film elements. By analyzing mirrored domain states, the pure in-plane and out-of-plane dynamic magnetic response under a continuous microwave excitation is extracted simultaneously. Domain-wall oscillations and local domain response, including transversely aligned and closure domain states, are visualized below, at, and above the resonance frequency of the magnetic elements. Regions of different high-frequency permeability are distinguished from the laterally resolved measurements. Despite nearly constant precessional frequency, a strong mode amplitude variation is found with varying the magnetic bias field, which is correlated to the exhibited change of the individual domain structure. Inhomogeneous out-of-phase precessional modes within the individual domains occur close to a state of domain instability. The imaging results are compared to existing models of flux response. Magnetic domain knowledge and precise dynamic imaging is needed for the understanding of the dynamic magnetization behavior of even basic domain structures beyond the magnetic material's elementary properties.

We have used a scanning Kerr microscope set-up with picosecond time resolution and sub-micron spatial resolution to directly measure the flux response in magnetic recording heads. The data rate limiting factor of a write head, which is the flux rise time at the gap, has been measured for different geometries and head materials in polar Kerr mode. Flux propagation in the yoke, which is governed by a combination of wall displacement and magnetization rotation, has been studied by one dimensional and two dimensional time response measurements utilizing the longitudinal Kerr effect. The local flux time response in the head was correlated to the respective micromagnetic structure as determined by static wide-field Kerr imaging. In addition to the intrinsic magnetic properties we have also studied the flux time response by looking at the system properties of the head/write-electronic and, by using a voltage source for excitation, information about classical eddy-current effects for different pole geometries have been derived. Further, non-stationary effects in the flux reversal process are shown to produce non-linearities in the response at the write gap which are contributing to non-linear transition shift in the write process.

In order to adjust the ferromagnetic resonance (FMR) frequency of thin NiFe films, ferromagnetic polycrystalline/amorphous NiFe/FeCoBSi bilayers using radio frequency magnetron sputtering were produced. Herein, the higher anisotropy field Hk of a ferromagnetic FeCoBSi was used to shift the FMR-frequency of the bilayer. Static and dynamic magnetic properties of the films were investigated by quasi-static magnetometry and by high frequency permeability measurements, respectively. The dynamic anisotropy field Hkdyn calculated from the FMR frequency of a single 100-nm NiFe-layer is shifted from mu0Hkdyn=0.5 mT to mu0Hkdyn=2.8 mT in a FeCoBSi(80 nm)/NiFe(20 nm) bilayer; whereas, the FMR frequency is congruently enhanced from 0.9 to 2.0 GHz. The permeability decreased from mu=2000 to mu=500. A linear dependence for the adjustment of the relevant magnetic parameters with NiFe:FeCoBSi ratio is demonstrated, opening the possibility to individually tailor magnetic properties of magnetic films for high-frequency applications

The influence of magnetic properties on the magnetization dynamics of high-resistivity amorphous CoZrTa thin films was investigated. A strong correlation with magnetic coercivity was found. Even small values of coercivity have an effect on the observed FMR frequency and the effective magnetic damping parameter /spl alpha/. The increased coercivity is due to a locally changing magnetic anisotropy distribution acting as a trap for the domain walls. The inhomogeneous anisotropy distribution in the films leads to additional frequency components observed during the dynamic remagnetization processes. The anisotropy field is measured directly from the dynamically obtained data. The observed dynamic response of the films makes them suitable for applications in the gigahertz regime.

Sputtered polycrystalline iron gratings with a varying stripe width between 0.5 and 3.7 /spl mu/m at a constant periodicity of 5 /spl mu/m were studied by Kerr microscopy. The magnetic anisotropy direction is aligned transverse to the stripe length axis. The observed domain processes are directly compared with hysteresis curve measurements. Domain nucleation and the resulting domain structure depend on the external magnetic field direction. Complicated multidomain states are observed down to a stripe width of 1.7 /spl mu/m. The most narrowly spaced stripes display a simple domain configuration with the average magnetization vector perpendicular to the stripes, along the full film anisotropy axis, indicating dipolar coupling between the elements. With decreasing stripe width and increasing stripe distance, a change to a Landau-Lifshitz-like domain pattern is found. For very narrow stripes, it transforms into a ripple modulated domain structure. Altogether, a continuous transition from full-film-like to single strip-like magnetization behavior with increasing stripe spacing is found. The results are explained by the existing uniaxial magnetic anisotropy together with the shape anisotropy increasing with reduced stripe width. The strong influence of coercivity on the magnetization patterns is shown.

The magnetodynamics of lens-shaped thin-film elements are studied using vector network analyzer ferromagnetic resonance. A strong increase in the frequency at resonance is found when approaching the switching field. From magnetic force microscopy imaging the increase in resonance frequency is ascribed to the formation and evolution of a buckling domain state. The experimental data are qualitatively reproduced by micromagnetic simulations of a model element. Thereby, the roles of the external magnetic field and the buckling wavelength are extracted separately. Magnetic domain modes with dynamic magnetization modulations parallel and perpendicular to the static magnetization are identified. Based on magnetostatic energy considerations qualitative arguments are derived that allow for an interpretation of the dynamic response in such low-symmetry magnetization distributions.

We report on the response of multilayer spin textures to static magnetic fields. Coupled magnetic vortex pairs in trilayer elements (ferromagnetic/nonmagnetic/ferromagnetic) are imaged directly by means of layer-selective magnetic x-ray microscopy. We observe two different circulation configurations with parallel and opposing senses of magnetization rotation at remanence. Upon application of a field, all of the vortex pairs investigated react with a displacement of their cores. For purely dipolar coupled pairs, the individual core displacements are similar to those of an isolated single-layer vortex, but also a noticeable effect of the mutual stray fields is detected. Vortex pairs that are linked by an additional interlayer exchange coupling (IEC), which is either ferromagnetic or antiferromagnetic, mainly exhibit a layer-congruent response. We find that, apart from a possible decoupling at higher fields, these strict IEC vortex pairs can be described by a single-layer model with effective material parameters. This result implies the possibility to design multilayer spin structures with arbitrary effective magnetization.

The concertina is a magnetization pattern in elongated thin-film elements of a soft ferromagnetic material. It is a ubiquitous domain pattern that occurs in the process of magnetization reversal in the direction of the long axis of the small element. Van den Berg and Vatvani [IEEE Trans. Magn. 18, 880 (1982)] argued that this pattern grows out of the flux-closure domains at the sample's tips as the external field is reduced. Based on experimental observations and theory, we argue that in sufficiently elongated thin-film elements the concertina pattern rather bifurcates from an oscillatory buckling mode. Typical sample widths and thicknesses are of the order of 10-100 $\ensuremath{\mu}$m and of the order of 10-150 nm, respectively. Using a reduced model that is derived by asymptotic analysis from the micromagnetic energy and that is also investigated by means of numerical simulation, we quantitatively predict the average period of the concertina pattern and qualitatively predict its hysteresis. In particular, we argue that the experimentally observed coarsening of the concertina pattern is due to secondary bifurcations related to an Eckhaus instability. We also link the concertina pattern to the magnetization ripple and discuss the effect of a weak (crystalline or induced) anisotropy.

Magnetization orientation in Ga${}^{+}$-irradiated Pt/Co(${d}_{\mathrm{Co}}$)/Pt ultrathin films can be changed in a controlled way by adjusting the ion fluence, $F$. Two-dimensional (${d}_{\mathrm{Co}}$, $F$) diagrams of magnetic and magneto-optical properties have been derived. Distinct out-of-plane magnetic anisotropy states with enhanced magneto-optical effects were evidenced for specific (${d}_{\mathrm{Co}}$, $F$) values. This rich behavior originates from two competing mechanisms: intermixing of Co and Pt atoms at the interfaces and the formation of ordered CoPt alloy phases with high magnetic anisotropy. The irradiation-induced effects open novel routes for both tailoring thin-film magnetic and magneto-optical properties and patterning of magnetic nanostructures.

A method for pinning synthetic antiferromagnet (SAF) based spin valves is presented, which allows pinning to be established perpendicular to the setting field H. As the SAF(AP1/Ru/AP2) magnetizes, its layer moments undergo a spin–flop transition for a magnetic field H=HSF and align with H for H=HSat. The magnetization of layer AP1 is perpendicular to H for a field H=HGold. This field corresponds to the maximum giant magnetoresistance GMR on HSF

We performed generalized Mueller matrix ellipsometry measurements in a magnetic field of arbitrary orientation and magnitude up to 400 mT at room temperature and probed the magneto-optical response of capped, ferromagnetic Fe, Ni${}_{20}$Fe${}_{80}$, Co, Ni${}_{80}$Fe${}_{20}$, and Ni thin films on ZnO substrates in the spectral range from 300 to 1100 nm. We determined the off-diagonal elements in the magneto-optical dielectric tensor under saturated magnetization conditions in the sample surface plane via a model analysis. The off-diagonal elements depend on the net spin polarization and the electronic band structure of the ferromagnetic thin films. For the pure ferromagnetic metals Fe, Co, and Ni, the converted off-diagonal elements agree well with the reported experimental optical conductivity data. As a result we use the extracted wavelength-dependent magneto-optical coupling constant to predict the wavelength-dependent magneto-optical response of different Ni/Fe multilayer structures.

The magnetic properties of FePt thin films have been modified by exposing the samples to irradiation of 4 MeV Cl2+ ions. Patterned magnetic films, without modified topographical profile, were fabricated by irradiating the films through a shadowing micrometric mask. The structural changes, ascribed to the ion-beam-induced amorphization of the thin films, promote the modification of the magnetic anisotropy. In particular, the out-of-plane component of the magnetization decreases simultaneously with an enhancement of in-plane anisotropy by increasing ion fluence. Moreover, the nonirradiated regions present unexpected anisotropic behavior owing to the stray field of the irradiated regions. The control of this effect, which can have unwished consequences for the patterning of magnetic properties by ion bombardment, needs to be suitably addressed, We gratefully acknowledge financial support from the Spanish Ministerio Ciencia e Innovacion through the project MAT2007-65420-C02-01 and Comunidad Autonoma de Madrid grant S2009/MAT-1467. MJ thanks Comunidad Autonoma de Madrid and CSIC Marina Bueno Program for their financial support. RS acknowledges the Spanish Ministry of Education and Science for a FPI research grant. JJ acknowledges the financial support from Linkoping University through the VR Linneaus grant LiLi-NFM

Magneto-optical properties of nominally 10, 20, and 30 nm thick ferromagnetic Ni films have been investigated at room temperature by vector-magneto-optical generalized ellipsometry under saturated magnetization conditions in the sample surface plane. The magneto-optical dielectric tensor of Ni has been determined by reflection Mueller matrix ellipsometry in the spectral range from 300 to 1100 nm. Different sets of magnetic field induced Mueller matrix elements enable us to identify the magnetization directions in the sample. The extracted magnetic field and thickness independent magneto-optical coupling constant is useful for modeling the Mueller matrix and complex Kerr angle of magnetized Ni thin films in layered sample systems in dependence of the incident angle of light, wavelength, and magnetization.

NiFe single layer and multilayer films laminated with amorphous Al/sub 2/O/sub 3/ interlayers were deposited by DC magnetron sputtering. The total ferromagnetic layer thickness was constant 1800 nm for the single and four layer lamination. Full film magnetic characterization revealed comparable soft magnetic properties for all samples. However, patterning the samples led to completely different domain and domain wall characteristics depending on the interlayer thickness. Influences of existing perpendicular anisotropy were observed by magneto-optical Kerr microscopy in the domain walls and closure domains of the structured samples. With increasing Al/sub 2/O/sub 3/ thickness the influence of perpendicular anisotropy on the domain patterns was reduced. At the largest interlayer thickness, the magnetization in each ferromagnetic layer behaves independently. The observed micromagnetic structures will be discussed.

International audience; The behavior of minor hysteresis loops in perpendicular anisotropy Co/Pt and Co/Pd multilayers has been investigated. Upon applying a succession of identical magnetic field cycles, we observe a very substantial cumulative growth of the minor loop area. For the Co/Pt multilayers this effect only saturates near complete magnetization reversal while the behavior is slightly more limited for Co/Pd multilayers. We also find this cumulative growth to occur even if the minor loop field cycles are made asymmetric by means of a positive bias field. The cumulative behavior persists up to a sample-dependent threshold value above which this effect disappears. In all samples, the cumulative minor loop growth is correlated with a small reduction in the maximum magnetization value in each cycle. Magneto-optical Kerr microscopy studies correlate the minor loop growth with the memory and cumulative expansion of lateral domain cycling. All experimental observations can be consistently explained as an accumulation of small nucleation domains that aid subsequent reversals and facilitate the cumulative minor loop growth.

The magnetization reversal in stripe-like exchange bias patterned $\rm Ni_{81}Fe_{19}/IrMn$ thin films was investigated by complementary inductive and high resolution magneto optical magnetometry, magneto optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange bias direction. Due to the interaction of interfacial coupling, exchange, and magneto-static energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micro-patterned exchange bias films., Comment: 10 pages, 9 figures, submitted to PRB

The magnetic anisotropy of amorphous thin films was modified laterally by masked ion irradiation without alteration of the intrinsic magnetic properties. The changes were introduced by local ion implantation in a protection layer, causing additional stress-induced magnetic anisotropy in the magnetostrictive layer. The underlying local variation of magnetic anisotropy was modelled and confirmed experimentally. The described method, relying purely on magneto-elastics, introduces a new path to the alteration of magnetic properties subsequent to magnetic film preparation. With the use of the resulting artificial magnetization patterns it is possible to tailor the ferromagnetic thin film structure used in magneto-electronic applications.

A dynamic phase transition (DPT) with respect to the period $P$ of an applied alternating magnetic field has been observed previously in numerical simulations of magnetic systems. However, experimental evidence for this DPT has thus far been limited to qualitative observations of hysteresis loop collapse in studies of hysteresis-loop area scaling. Here, we present significantly stronger evidence for the experimental observation of this DPT in a ${[\text{Co}(4\text{ }\text{\AA{}})/\text{Pt}(7\text{ }\text{\AA{}})]}_{3}$-multilayer system with strong perpendicular anisotropy. We applied an out-of-plane time-varying (sawtooth) field to the ${[\text{Co}/\text{Pt}]}_{3}$ multilayer in the presence of a small additional constant field, ${H}_{b}$. We then measured the resulting out-of-plane magnetization time series to produce nonequilibrium phase diagrams (NEPDs) of the cycle-averaged magnetization, $Q$, and its variance, ${\ensuremath{\sigma}}^{2}(Q)$, as functions of $P$ and ${H}_{b}$. The experimental NEPDs are found to strongly resemble those calculated from simulations of a kinetic Ising model under analogous conditions. The similarity of the experimental and simulated NEPDs, in particular the presence of a localized peak in the variance ${\ensuremath{\sigma}}^{2}(Q)$ in the experimental results, constitutes strong evidence for the presence of this DPT in our magnetic multilayer samples. Technical challenges related to the hysteretic nature and response time of the electromagnet used to generate the time-varying applied field precluded us from extracting meaningful critical scaling exponents from the current data. However, based on our results, we propose refinements to the experimental procedure which could potentially enable the determination of critical exponents in the future.

International audience; The mechanism of chirality reversal for a planar interface domain wall in a hard/soft magnetic bilayer has been identified by combining magnetoresistance measurements, modeling, and direct magnetic domain observations. The reversal occurs through IDW nucleation and lateral domain wall propagation. Over an unpredicted wide range of applied magnetic fields, the chirality transition takes place by an unwinding followed by a rewinding of the IDW. The chirality transition mechanism of phase transition could be identified from a micromagnetic analysis of the lateral magnetic domain wall orientation. Up to three magnetization phases coexist in the uniaxial material during reversal.

The use of femtosecond laser pulses generated by a Ti:Sapphire laser system allows us to gain an insight into the magnetization dynamics on time scales from sub-picosecond up to 1 ns directly in the time domain. This experimental technique is used to excite a polycrystalline nickel (Ni) film optically and probe the dynamics afterwards. Different spin wave modes (the Kittel mode, perpendicular standing spin-wave modes (PSSW) and dipolar spin-wave modes (Damon-Eshbach modes)) are identified as the Ni thickness is increased. The Kittel mode allows determination of the Gilbert damping parameter alpha extracted from the magnetization relaxation time tau_alpha. The non-local damping by spin currents emitted into a non-magnetic metallic layer of vanadium (V), palladium (Pd) and the rare earth dysprosium (Dy) are studied for wedge-shaped Ni films 1 nm-30 nm. The damping parameter increases from alpha=0.045 intrinsic for nickel to alpha>0.10 for the heavy materials, such as Pd and Dy, for the thinnest Ni films below 10 nm thickness. Also, for the thinnest reference Ni film thickness, an increased magnetic damping below 4 nm is observed. The origin of this increase is discussed within the framework of line broadening by locally different precessional frequencies within the laser spot region.

A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias stripes. The lateral structure is imprinted into a continuous ferromagnetic/antiferromagnetic exchange-bias bi-layer via laterally selective exposure to He-ion irradiation in an applied field. This creates an alternating frozen-in interfacial exchange bias field competing with the external field in the course of the re-magnetization. It was found that in a magnetic field applied at an angle with respect to the exchange bias axis parallel to the stripes the re-magnetization process proceeds via a variety of different stages. They include coherent rotation of magnetization towards the exchange bias axis, precipitation of small random (ripple) domains, formation of a stripe-like alternation of the magnetization, and development of a state in which the magnetization forms large hyper-domains comprising a number of stripes. Each of those magnetic states is quantitatively characterized via the comprehensive analysis of data on specular and off-specular polarized neutron reflectivity. The results are discussed within a phenomenological model containing a few parameters which can readily be controlled by designing systems with a desired configuration of magnetic moments of micro- and nano-elements., 11 pages, 7 figures

We present magnetization and Kerr microscopy measurements of the exchange-bias training effect in hard/soft, ${\mathrm{Tb}}_{12}{\mathrm{Fe}}_{88}$/${\mathrm{Gd}}_{40}{\mathrm{Fe}}_{60}$, bilayers. These experimental results, compared with micromagnetic simulations, unambiguously show the role of the soft GdFe layer reversal on irreversible magnetic changes in the hard TbFe layer. After a partial reversal of the GdFe magnetization layer, the next field cycle exhibits a double hysteresis loop which is due to the existence of two types of domains in the sample, and only one of these domains has been subject to the training effect. The antiferromagnetically interfacial coupling and positive exchange-bias shift permit us to exclude any direct contribution from the magnetic field to this mechanism.

The observation of magnetic domains by magneto-optical microscopy, based on the Kerr and the Faraday effect, is one of the most prominent techniques for the visualization of distributions of magnetization within magnetic materials. The method has gained increased attention due to the possibility to visualize field and current induced phenomena in nanostructured magnetic materials on fast time-scales. Fundamental concepts and recent advances in methodology are discussed in order to provide guidance on the usage of wide-field magneto-optical microscopy in applied magnetism. Recent applications of magneto-optical microscopy in bulk and thin film materials are reviewed at the end.

The static and dynamic magnetic properties, especially the magnetic damping behavior, have been investigated as a function of saturation magnetization in thin Permalloy films. Ion implantation doping with Cr in the percentage regime has been used to effectively reduce the Curie temperature and the saturation magnetization at room temperature. In order to understand the magnetic modifications the changes in stoichiometry but also the ion-induced structural changes have been addressed. As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion, and finally a partial amorphization of the interface near region of the Permalloy layer are found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation-induced damage formation. The magnetic properties change correspondingly. For increasing Cr doping a drop in saturation magnetization and a decrease of the uniaxial magnetic anisotropy is observed. For a fluence of $0.8\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}\mathrm{Cr}∕{\mathrm{cm}}^{2}$ $(\ensuremath{\approx}4\phantom{\rule{0.3em}{0ex}}\mathrm{at}.\phantom{\rule{0.2em}{0ex}}%)$ the magnetic damping parameter $\ensuremath{\alpha}$ increases by a factor of more than 3. This strong increase is mainly caused by doping effects.

We have investigated the magnetization arrangement in an in-plane stripe pattern with alternating exchange-bias domains. The stripe pattern was produced by ion bombardment induced magnetic patterning, which changed locally the exchange-bias direction at the ferromagnet/antiferromagnet interface, but not the magnetic or antiferromagnetic properties of the Co70Fe30 and Mn83Ir17 layers, respectively. For the analysis of the magnetic domain structure evolution along the hysteresis loop we used a combination of experimental techniques: magneto-optical Kerr effect, Kerr microscopy, polarized neutron reflectometry, and off-specular scattering of polarized neutrons with polarization analysis. Instead of a perfect antiparallel alignment we found that the magnetization in neighboring stripes is periodically canted with respect to the stripe axis so that the net magnetization of the ferromagnetic film turns almost perpendicular to the stripes. At the same time the projection of the magnetization vector onto the stripe axis has a periodically alternating sign. The experimental observations are explained and quantitatively described within the frame of a phenomenological model, taking into account interfacial exchange bias, intralayer exchange energy, and uniaxial anisotropy. The model defines conditions which can be used for tailoring nano- and micro-patterned exchange-bias systems with different types of magnetic order.

The layer magnetization, the saturation magnetization as well as the magnetic anisotropy, and damping behavior of 20nm thick Ni81Fe19 films have been modified by 30keV Ni ion implantation with fluences up to 1×1016Ni∕cm2 (≈5at.%). With increasing ion fluence a magnetic dead layer of increasing thickness is formed which leads to a reduction of the total magnetization. In addition, the saturation magnetization of the residual ferromagnetic film decreases due to, both, a shift in stoichiometry and radiation damage. Accordingly a reduction of the magnetic anisotropy and a strong enhancement of the magnetic damping parameter are observed. Moreover, ion implantation in an applied magnetic field allows the setting of the uniaxial anisotropy direction irrespective of its original orientation. Static and dynamic magnetic properties of Ni81Fe19 films can be tailored over a wide range after film deposition.

The switching of extended ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ thin film elements with a thickness of $50\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and various shapes (squared, rectangular, pointed) has been studied by time-resolved stroboscopic Kerr microscopy based on a conventional wide-field optical polarization microscope. The elements are deposited on coplanar strip-lines that generate field pulses driven by electronic pulse generators. Time resolution is obtained by imaging with a gated and intensified charge-coupled device camera. The opening can be varied from $250\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ to continuous exposure, allowing the comparison of fast magnetization processes and quasistatic switching in slowly varying fields. The latter is typically characterized by the formation of a concertina domain pattern that irreversibly decays in a multidomain ground state by the abrupt motion of vortices and domain walls. After excitation with fast field pulses similar blocked patterns are formed. They dissolve by spatially inhomogeneous rotational processes involving cross-tie-wall-like domain boundaries.

The understanding and the modification of the magnetic damping processes in thin ferromagnetic films has gained considerable interest in recent years. In addition to applied research on ultrafast magnetization reversal [1-3] also studies concerning the basic damping phenomena [4,5] and their modification by means of adjacent non-magnetic layers [6] or alloying [7] have been reported. Also the use of ion implantation to modify magnetic properties on a local scale has been addressed [8]. Here we report on investigations of the static and dynamic magnetic properties of 20 nm thick permalloy films as prepared and after 30 keV Cr implantation with different Cr fluences. Due to the doping the Curie temperature of the permalloy film decreases with the implantation fluence. At an averaged Cr concentration of about 7% (≈ 1.4·10^16 Cr/cm^2) the Curie temperature drops below room temperature. The uniaxial anisotropy, induced by a magnetic field during deposition, decreases but persists with increasing Cr fluence as indicated by the 2-fold symmetry of the magnetic remanence as a function of in-plane angle measured by magneto-optic Kerr effect magnetometry. In order to investigate the magnetization damping pulsed inductive microwave magnetometry (PIMM) has been performed for various applied magnetic fields. In Fig. 3 the magnetization traces for the as-deposited permalloy film as well as the Cr-implanted samples are shown for an applied field of 10 Oe. Upon Cr implantation the PIMM amplitude is decreased consistent with a decrease in the uniaxial anisotropy AND a reduction in saturation magnetization. This results in a decrease of the precession frequency which is easily observed. However, the magnetic damping, i. e. the relaxation of the precession, is also altered by the Cr implantation. A detailed analysis of the damping parameter leads to 7-fold increase of the damping for only 4% of Cr doping. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated. References [1] T. Gerrits, H. A. M. van den Berg, J. Hohlfeld, O. Gielkens, L. Bär, Th. Rasing, Nature 418, 509 (2002). [2] S. Kaka, S. Russek, Appl. Phys. Lett. 80, 1958 (2002). [3] H. W. Schumacher, C. Chappert, P. Crozat, R. C. Sousa, P. P. Freitas, J. Miltat, J. Fassbender, B. Hillebrands, Phys. Rev. Lett. 90, 017201 (2003). [4] D. L. Mills, S. M. Rezende, Topics in Applied Physics 87, 27 (2003). [5] B. Heinrich, in Ultrathin Magnetic Structures III, IV, edited by B. Heinrich and J. A. C. Bland (Springer-Verlag, Berlin, 2003). [6] S. Mizukami, Y. Ando, T. Miyazaki, Jap. J. Appl. Phys. 40, 580 (2001). [7] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003). [8] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).