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Recent results showed that the ferrimagnetic compensation point and other characteristic features of Tb/Co ferrimagnetic multilayers can be tailored by He+ ion bombardment. With appropriate choices of the He+ ion dose, we prepared two types of lattices composed of squares with either Tb or Co domination. The magnetization reversal of the first lattice is similar to that seen in ferromagnetic heterostructures consisting of areas with different switching fields. However, in the second lattice, the creation of domains without accompanying domain walls is possible. These domain patterns are particularly stable because they simultaneously lower the demagnetizing energy and the energy associated with the presence of domain walls (exchange and anisotropy). For both lattices, studies of magnetization reversal show that this process takes place by the propagation of the domain walls. If they are not present at the onset, the reversal starts from the nucleation of reversed domains and it is followed by domain wall propagation. The magnetization reversal process does not depend significantly on the relative sign of the effective magnetization in areas separated by domain walls.

Single and double paramagnetic colloidal particles are placed above a magnetic square pattern and are driven with an external magnetic field processing around a high symmetry direction of the pattern. The external magnetic field and that of the pattern confine the colloids into lanes parallel to a lattice vector of the pattern. The precession of the external field causes traveling minima of the magnetic potential along the direction of the lanes. At sufficiently high frequencies of modulation, only the doublets respond to the external field and move in direction of the traveling minima along the lanes, while the single colloids cannot follow and remain static. We show how the doublets can induce a coordinated motion of the single colloids building colloidal trains made of a chain of several single colloids transported by doublets.

Edge currents of paramagnetic colloidal particles propagate at the edge between two topologically equivalent magnetic lattices of different lattice constant when the system is driven with periodic modulation loops of an external magnetic field. The number of topologically protected particle edge transport modes is not determined by a bulk-boundary correspondence. Instead, we find a rich variety of edge transport modes that depend on the symmetry of both the edge and the modulation loop. The edge transport can be ratchet-like or adiabatic, time or non-time reversal symmetric. The topological nature of the edge transport is classified by a set of winding numbers around bulk fence points extended by winding numbers around edge specific bifurcation points that cannot be deduced from the two bulk lattices.

Paramagnetic colloidal spheres assemble to colloidal bipeds of various length in an external magnetic field. When the bipeds reside above a magnetic pattern and we modulate the direction of the external magnetic field, the rods perform topologically distinct classes of protected motion above the pattern. The topological protection allows each class to be robust against small continuous deformations of the driving loop of the external field. We observe motion of the rod from a passive central sliding and rolling motion for short bipeds toward a walking motion with both ends of the rod alternately touching down on the pattern for long bipeds. The change of character of the motion occurs in form of discrete topological transitions. The topological protection makes walking a form of motion robust against the breaking of the non symmorphic symmetry. In patterns with non symmorphic symmetry walking is reversible. In symmorphic patterns lacking a glide plane the walking can be irreversible or reversible involving or not involving ratchet jumps. Using different gauges allows us to unravel the active and passive aspects of the topological walks.

We show that it is possible to engineer magnetic multidomain configurations without domain walls in a prototypical rare-earth-transition-metal ferrimagnet using keV He^{+} ion bombardment. We additionally show that these patterns display a particularly stable magnetic configuration due to a deep minimum in the energy of the system caused by flux closure and a corresponding reduction of the magnetostatic energy without an increase in energy by exchange and anisotropy terms across the walls. This occurs because light-ion bombardment affects an element's relative contribution to the properties of the ferrimagnet differently. Therefore, it is possible to control the relative contribution from each magnetic subsystem. The selection of material and the use of light-ion bombardment allow us to engineer domain patterns in continuous magnetic films, which open a way to fabricate them in a much smaller scale than currently possible. Our Letter emphasizes that the right criterion to determine the presence or absence of a domain wall is whether there is a rotation of the spin for each sublattice and that changes of the direction of effective magnetization alone do not constitute an appropriate criterion.

Deposition of alloy films with a well-controlled concentration gradient obtained by co-sputtering from two magnetron sources is studied experimentally and compared with numerical calculations. This method was used together with a linearly moving shutter to fabricate sperimagnetic Co-Tb alloy films with mutually orthogonal concentration and thickness gradients. Using magnetooptical measurements it was demonstrated that, for thicknesses below 10 nm, the compensation concentration (ccomp) shifts towards higher Tb content as the thickness of the Co-Tb film is reduced. Results for Co-Tb alloy films are compared with those for (Tb/Co)RN multilayers with various repetition numbers (RN). For both sample types, the ccomp decreases in a similar way with increasing total film thickness. Thus, the decrease of ccomp with increasing total thickness (either of alloy films or of multilayers) can be considered a universal behavior.

A magnetic multilayer of substrate/Pt-15 nm/Co-0.8 nm/Pt-wedge 0–7 nm/Co-0.6 nm/Pt-2 nm structure is characterized by a perpendicular anisotropy of the Co layers and by graded interlayer coupling between them. Using magnetooptical Kerr microscopy we observed a distinct influence of magnetic domains in one Co layer on the nucleation field and positions of nucleation sites of reversed domains in the second Co layer. For sufficiently strong interlayer coupling a replication of magnetic domains from the magnetically harder layer to the magnetically softer layer is observed.

Magnetophoresis of micrometer sized superparamagnetic beads on sputtered Ir/Co(1.2 nm)/Ir multilayers with perpendicular magnetic anisotropy has been investigated. We show that domain walls motion in these layer systems is controlling the motion of the beads in an aqueous environment, where the domain wall motion is induced by varying perpendicular external magnetic fields of several kA/m. The magnetic fields of the Neel type walls, and forces calculated based on micromagnetic simulations of their structure, are consistent with viscous forces observed in the experiment. We show that the cylindrical domains can be used to efficiently gather originally scattered beads in a small area.

The ability to perform wide-range tuning of the magnetic field required to switch the magnetization of ferromagnetic layers with perpendicular magnetic anisotropy is of great importance for many applications. We show that, for (Au/Co)2(3) multilayers, this field can be changed from minus several kOe to plus several kOe because of changes to the coupling with a ferrimagnetic multilayer [either (Tb/Fe)6 or (Tb/Co)6] across a Au spacer (either homogeneous 1 nm thick or wedge-shaped). The adjustable parameters are the ratio of sublayer thicknesses of the ferrimagnet and the sequence of layers around the Au spacer. The change of the sequence from Co/Au/Co to Tb/Au/Co is accompanied by both the reduction of the interaction energy and the change of the magnetic field sign necessary to switch the magnetization of ferromagnetic multilayers. For a 1 nm thick Au spacer this fields change from positive (negative) to negative (positive) if the ferrimagnet is dominated by the transition metal (rare earth) as a result of its composition. The characteristic oscillatory behavior of RKKY-like coupling is demonstrated using a system with a wedge-shaped Au spacer.

Colloidal magnetophoretic lensing of water suspended micrometer-sized superparamagnetic beads (SPBs) above a topographically patterned magnetic thin film system with perpendicular magnetic anisotropy is demonstrated. The magnetic pattern consisting of concentric annuli of micron-sized widths has been superimposed with a rotating external magnetic field, and it is shown that the trajectories of the SPBs above this structure are similar to light rays in an optical focusing lens. SPB trajectories converge towards the central region and have divergent trajectories while passing the center. The experimental findings are corroborated by a quantitative model for the SPB trajectories. The magnetophoretic lensing effect leads to a high SPB concentration in the center of the pattern and may be useful for applications where SPBs have to approach each other in a controlled way.

The topologically protected transport of colloidal particles on top of periodic magnetic patterns is studied experimentally, theoretically, and with computer simulations. To uncover the interplay between topology and symmetry we use patterns of all possible two dimensional magnetic point group symmetries with equal lengths lattice vectors. Transport of colloids is achieved by modulating the potential with external, homogeneous but time dependent magnetic fields. The modulation loops can be classified into topologically distinct classes. All loops falling into the same class cause motion in the same direction, making the transport robust against internal and external perturbations. We show that the lattice symmetry has a profound influence on the transport modes, the accessibility of transport networks, and the individual transport directions of paramagnetic and diamagnetic colloidal particles. We show how the transport of colloidal particles above a two fold symmetric stripe pattern changes from universal adiabatic transport at large elevations via a topologically protected ratchet motion at intermediate elevations toward a non-transport regime at low elevations. Transport above four-fold symmetric patterns is closely related to the two-fold symmetric case. The three-fold symmetric case however consists of a whole family of patterns that continuously vary with a phase variable. We show how this family can be divided into two topologically distinct classes supporting different transport modes and being protected by proper and improper six fold symmetries. We discuss and experimentally demonstrate the topological transition between both classes. All three-fold symmetric patterns support independent transport directions of paramagnetic and diamagnetic particles. The similarities and the differences in the lattice symmetry protected transport of classical over-damped colloidal particles versus the topologically protected transport in quantum mechanical systems are emphasized.

Detailed knowledge of various couplings present in magnetic thin film systems could contribute to a better predictability of devices. In ferromagnetic multilayers with a perpendicular magnetic anisotropy, a correlated waviness can lead to antiferromagetic coupling between adja-cent layers (Neel's coupling). We show, using micromagnetic simulations, that the coupling energy depends strongly on layers separation and on details of interface profiles. We show, too, that the coupling is slightly field dependent.

The thermoelectric effects in three-terminal structures with a quantum dot are considered. We propose the experimentally consistent protocol for determination of the transport coefficients in terms of the local and non-local conductances and thermopowers that can be measured in two steps, applying the `four probe technique'. This proposal is compared with other approaches discussed so far in the literature. As an example we study in detail the thermopower induced by the superconducting electrode in a subgap regime which might be useful for analysis of novel hybrid devices.

We measure magnetization reversal and giant magnetoresistance of CoFe/Au/Co/Au multilayers and use micromagnetic simulations to model them. We characterize the system by perpendicular and easy-plane effective anisotropy of Co and CoFe layers, respectively. We show that minor hystereses of magnetoresistance can be reasonably well described by the model. The simulations show that the variation of resistance with the field depends on the field strength at which the sweep reverses, and is correlated with the number of stripe domains present in the Co layers.

[Co83Fe17/Au/Co/Au]N sputter deposited multilayers displaying a giant magnetoresistance have been investigated. Complementary magnetic measurements were conducted in order to characterize a spin reorientation transition in Co83Fe17 layers sandwiched between Au spacers. The transition from a perpendicular magnetic anisotropy to easy-plane one takes place at the thickness of about 1 nm.

Here, we systematically investigated the influence of ion bombardment with different fluences on the strength and direction of the exchange bias coupling in Au/Co/NiO systems with perpendicular magnetic anisotropy of the Co layer. We found that the direction of the exchange bias coupling can be reversed as a result of ion bombardment performed in an external magnetic field which is in the opposite direction to the magnetic field applied during film deposition. Moreover, the strength of the exchange bias coupling can be tailored by varying the ion fluence. These results show behaviors similar to the results found for systems of ferromagnetic layers with in-plane anisotropy. Our experimental work, supported by a two-energy-level model, demonstrates that exchange bias coupling can be tuned in a layered system with perpendicular magnetic anisotropy using ion bombardment.

Magnetic hysteresis of [ CoFe / Au / Co / Au ] N multilayers displaying giant magnetoresistance was investigated. It is shown that an effective coupling between the neighboring magnetic layers can be modified by the changes of the structure of the multilayers. It is shown, too, that this coupling is influenced by temperature. Some of the observed dependencies are explained on the basis of micromagnetic simulations.

Results of domain structures observation of individual Ni80Fe20 and Co sublayers in sputter deposited (NiFe/Au/Co/Au)10 multilayers, using an element-sensitive method: the photoemission electron microscopy combined with soft X-ray magnetic circular dichroism, are presented. Also, overall domain structures were studied with magnetic force microscopy. The studies allowed us to reveal submicron stripe domains in the investigated samples and the replication of the stripe domains from the Co layers with perpendicular anisotropy to the NiFe layers with easy-plane anisotropy.

Material selective sensitivity of a magneto-optical polar Kerr effect to magnetizations of films from different materials in a multilayer system is presented. The method is supported by rigorous modeling of magneto-optic response from the multilayer system and by experimental demonstration on the periodic cobalt-permalloy multilayers [Ni80Fe20(2 nm)/Au(2 nm)/Co(0.4, 0.8, and 1.2 nm)/Au(2 nm)]10 .

The magnetic properties of an ultrathin cobalt film were modified by a focused femtosecond pulsed laser beam. The Co wedge, with a thickness ranging from 0 to 2 nm, sandwiched by Au films was prepared using ultra-high vacuum magnetron sputtering on a mica substrate. The modifications of the laser induced magnetic anisotropy were investigated using magneto-optic Kerr microscopy and MFM/AFM techniques. The laser induces: (i) local reorientation of magnetization from an in-plane to a perpendicular state and (ii) an increase of the coercivity field. A corresponding increase of the perpendicular magnetic anisotropy is discussed considering an improvement of the Co/Au interfaces.

The influence of annealing on a giant magnetoresistance, magnetization reversal, and microstructure of magnetron sputtered spin valve [NiFe/Au/Co/Au] 10 multilayers (MLs) consisting of ferromagnetic layers with alternating in-plane (NiFe) and out-of-plane (Co) magnetic anisotropy has been investigated. It is shown that properties of the MLs are relatively stable against annealing up to 263 ° C and are primarily influenced by mixing at Au/Co interfaces. The MLs with thicker Co layers are more stable.

A new type of spin valve (SV) structure consisting of ferromagnetic layers, with the in-plane ( F ‖ ) and out-of-plane ( F ⊥ ) anisotropy, separated by a non-magnetic spacer is proposed. We have chosen thin Co layers, sandwiched between Au ones, as those with perpendicular anisotropy. Our measurements have proved that the Co layers show perpendicular anisotropy for 0.4 t Co t Co > 1.8 nm. As ferromagnetic layers with the in-plane anisotropy ( F ‖ ), we have applied either Ni–Fe (1 ≤ t NiFe ≤ 4 nm) or Co ( t Co = 3.2 nm) layers. For both types of structures, i.e., the multilayers [NiFe/Au/Co ⊥ /Au] N and [Co ‖ /Au/Co ⊥ /Au] N , where N is number of repetitions, deposited by the magnetron sputtering, the GMR effect of up to 9% at room temperature is accompanied by a linear and almost non-hysteretic R ( H ) dependence. GMR is resistant to annealing up to T A ≤ 525 K.

The magnetic properties of sputtered [Ni80Fe20(2 nm)/Au(tAu)/Co(tCo)/Au(tAu)]15 multilayers with tAu = 1.5-3 nm and tCo =0.6-1.5 nm were investigated with magnetic force microscope. The Ni80Fe20 layers possessed in-plane magnetic anisotropy while the sandwiching of Co layers between Au layers ensured their perpendicular anisotropy through the influence of surface anisotropy. It led to the formation of a maze configuration of stripe domains. The stripe domains period λ strongly depends on tCo changing from 0.9 to 0.3 µm when tCo changes from 0.6 to 0.8 nm. Period λ increases with Au layers thickness, too. The values of stray fields originating from Co layers which act on Ni80Fe20 layers, in the range of 100 kA/m, estimated from magnetoresistive dependencies are in qualitative agreement with those evaluated from the model of infinitely long stripe domains with domain widths taken from MFM measurements. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Sputtered Ni 80 Fe 20 /Au/Co/Au multilayers (MLs) exhibit perpendicular anisotropy of Co layers and easy-plane anisotropy of Permalloy layers. In these samples the changes of relative orientation of magnetization between Co and NiFe layers, with magnetic field, can be determined by magnetoresistance measurements. The magnetic structure is discussed for two types of Ni 80 Fe 20 /Au/Co/Au MLs characterized by a weak coupling between ferromagnetic layers: (i) MLs with rectangular hysteresis loops and small coercive field, (ii) MLs with dense stripe domain structure in Co layers.

In this contribution the influence of annealing on magnetization reversal and on the giant magnetoresistance effect of [Ni 80 Fe 20 /Au(t Au )/Co(t Co )/Au(t Au )] 10 multilayers with t Co = 0.6, 0.8 nm and t Au = 1.5, 2.2 nm was studied. Measurements performed for as-deposited samples and after subsequent annealing at T a (423 K < T a < 523 K) show that the GMR effect is stable under annealing below 475 K. It even slightly increases, for T a above 450 K, opening a path for a GMR value control and therefore is important for applications. The most pronounced changes were observed in the saturation field H Co S ∥ which is a measure of perpendicular anisotropy. The significant variations were also noticed in the central part of the M(H) and R(H) curves. They are characterized by the nucleation field H N and the saturation field H S ⊥ which are related to the appearance and disappearance of stripe domains in Co layers, respectively. The influence of T a on values of H Co S ∥, H S ⊥ and H N will be discussed.

Magnetic and magnetotransport properties of (Ni80Fe20/Au/Co/Au)N multilayers with tCo = 0.6 nm and different thicknesses of Au layers (1.5 ≤ tAu ≤ 2.2 nm) have been investigated. The Co layer thickness used ensures its perpendicular anisotropy. We argue that in a hysteretic region of R(H) and M(H) dependencies the reorientation of Py layers is strongly influenced by the magnetic stray fields originating from the domain structure of Co layers. The values of stray fields are determined from R(H) and M(H) measurements and are compared with the calculated ones. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of Ar-ion irradiation on the microstructure, interlayer coupling and giant magnetoresistance (GMR) effect in the model Fe/Cr system was studied by the conversion electron Mossbauer spectrometry (CEMS), vibrating sample magnetometry (VSM), and magnetoresistivity, for the Fe-1.4 nm/Cr- t Cr multilayers with t Cr ranging from 0.73 to 1.85 nm. The loss of antiferromagnetic coupling and the simultaneous degradation of GMR, observed for increasing ion dose, was caused by the formation of pinholes due to the increase of interface roughness and at high ion doses, by the ion-beam mixing leading to the alloying of Fe and Cr at interfaces.

The influence of Ar-ion irradiation on the microstructure, interlayer coupling and magnetoresistance in Fe/Cr multilayers is studied. An increase of interface roughness of Fe/Cr multilayers caused by irradiation with 200 keV Ar ions and doses exceeding 5 × 1012 Ar/cm2 is clearly seen in conversion electron Mossbauer spectroscopy (CEMS) measurements, while the small angle X-ray diffraction (SAXRD) technique hardly detects such changes in microstructure even at the higher ion doses. This subtle modification of the microstructure induces distinct changes in magnetization reversal (increase of the remanence magnetization, decrease of the saturation fields) and strongly decreases GMR effect with increasing irradiation dose. The most prominent changes are observed for the samples with a small thickness of Cr layers. The increasing immunity of GMR effect to ion irradiation with the increasing thickness of Cr layers as well as correlation between changes in GMR and antiferromagnetically coupled sample fraction suggest that the main effect responsible for the decrease of GMR is caused by the pinholes creation. For doses exceeding 2 × 1013 Ar/cm2 the volume intermixing seems to be a dominating mechanism responsible for further degradation of GMR and antiferromagnetic interlayer exchange coupling.

The magnetic properties of sputtered (Ni_(83)Fe_(17)/Au/Co/Au) multilayers with various thicknesses of Au (0.5 ≤ t_(Au) ≤ 3 ㎚), Ni-Fe (1 ≤ t_(Ni-Fe) ≤ 4 ㎚) and Co (0.2 ≤ t_(Co) ≤ 1.5 ㎚) layers were characterized. An alternating inplane and out-of-plane anisotropy of the ferromagnetic layers was achieved for the structures (t_(Au)≥ 1.5 ㎚) showing a weak coupling between the Ni-Fe layers with an in-plane anisotropy and the Co layers (0.3 ≤ t_(Co) ≤ 1.2 ㎚) with a perpendicular anisotropy. For such a structure, a detailed discussion on the GMR effect is presented, relating to the magnetization reversal from a mutually perpendicular magnetic configuration at the remanence to a parallel one at the saturation. An influence of the dense labyrinth domain structure on the magnetoresistance effect is also addressed.

The magnetic properties of the sputter-deposited Cu/NiFe/MnIr/CoFe/Al+Ox/NiFe/Ta system are investigated to create a magnetically optimized TMR system and to tailor the magnetic properties. The unidirectional exchange anisotropy was found to depend strongly on the MnIr layer thickness with no exchange bias for t(MnIr) less than or equal to 5 nm and decreasing bias for t(MnIr) greater than or equal to 10 rim. For t(MnIr) = 15 nm exchange coupling energy was found to be 0.17 mJ/m(2) and the blocking temperature reaches 500 K. The thickness of the CoFe layer was found to strongly influence the shift of the magnetization loop of the upper NiFe layer by magnetostatic coupling. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The magnetoresistive properties of sputtered spin-valve-like Co(t Co1 )/Cu/Co(t Co2 ) multilayers with alternating thicknesses of Co sublayers are investigated. It is shown that annealing at temperatures up to 573 K enhances a magnetoresistance ratio but does not reduce a hysterecity of a R(H) dependence. It is also shown that multilayers with thinner Co sublayers are relatively more stable at higher annealing temperatures.

Graded anisotropy magnetic materials possess a coercive field changing laterally with position. A simple fabrication procedure to produce such an anisotropy gradient in a polycrystalline Au/Co layer system without lateral thickness variation and with perpendicular magnetic anisotropy, prototypical for a large variety of thin film systems, is shown. The procedure uses light-ion bombardment without the use of a mask. Magnetization reversal in this polycrystalline layer system takes place by unidirectional movement of a single domain wall only in regions with larger anisotropies and anisotropy gradients. In this anisotropy/anisotropy gradient regime, the domain wall is oriented perpendicular to the coercive field gradient, and it can be positioned along the gradient by an appropriate magnetic field pulse. For smaller anisotropies/anisotropy gradients, the natural anisotropy fluctuations of the polycrystalline layer system induce magnetization reversal dominated by domain nucleation. PACS 75.30.Gw; 75.70.Cn; 75.60.Ch

Metal-oxide ${\mathrm{[Fe}}_{K}/(\text{MgO}){}_{L}{\mathrm{]}}_{N}$ multilayers were grown on MgO(001) substrates for various integer numbers $(K,L)$ of the Fe(001) and MgO(001) monolayers, respectively, and the number of repetitions $N$ varied from 6 to 30. Room-temperature conversion electron M\"ossbauer spectroscopy (CEMS) measurements proved that the magnetic properties of these monoatomic multilayers were extremely sensitive to both the Fe and MgO sublayer thicknesses. A stable ferromagnetic state and a strong perpendicular magnetization component at room temperature were obtained by changing the sublayer thickness and the number of multilayer repetitions. The analysis of the CEMS spectra in correlation with the magneto-optic Kerr effect measurements indicated a complicated domain structure in this special type of metal-insulator material. The vortexlike domain structure was confirmed by micromagnetic simulations.

The influence of annealing on giant magnetoresistance (GMR) effect and magnetization reversal processes has been investigated in Py/Cu (Py = Ni 83 Fe 17 ) sputter-deposited multilayers (MLs) with a limited number of magnetic sublayers (N ≤ 6) and equal sublayer thicknesses both for Py and Cu (t Cu = 2 nm, t Py = 2 nm). Based on the magnetization and magnetoresistance measurements it has been shown that the magnetic behavior of such MLs is strongly influenced by annealing driven disruption of magnetic layers (lateral decoupling) and nonmagnetic layers (magnetic bridging between Py layers). A comparison of experimental hysteresis curves with model dependences indicates that annealing causes a change of the magnetization reversal from a local to an absolute energy minimum mode leading to quasi-two-state magnetoresistance characteristics.

The coupling between permalloy and cobalt layers (characterized by in-plane and perpendicular anisotropy, respectively) in NiFe/Au/Co/Au sandwich films and multilayers was investigated. In sandwich samples the main contribution to the effective coupling comes from the structural imperfections (pinholes and interface roughness). For multilayers, due to creation of dense stripe domains in Co layers, the supplementary coupling is observed in the field range defined by the nucleation and annihilation of the domains.

The investigation of thermal stability of sputtered permalloy/copper multilayers with various Cu sublayer thicknesses was performed. The observed changes of antiferromagnetically coupled fraction of multilayers, their magnetoresistance, and shape of the hysteresis loop with increasing annealing temperature are, in our opinion, a consequence of grain boundary diffusion creating the magnetic bridges (pinholes) across the Cu sublayer. It is demonstrated that the high sensitive giant magnetoresistance observed for permalloy/copper multilayers with Cu sublayer thickness equal to about 2 nm is not destroyed by annealing at temperatures up to 175°C.

The thickness dependence of magnetoresistance was studied for a series of thin Co 20 Ag 80 films. The room temperature magnetoresistance in perpendicular configuration (CIP) was measured for as-deposited and annealed samples in fields up to 2 T. All samples were annealed for 10 min at temperatures ranging from 423 to 623 K at steps of 100 K. MR values growing with the thickness t were observed. MR varies steeply for small t and saturates at larger thicknesses. Changes of the width of the MR curve with the film thickness were also analyzed.

The magnetophoresis of water-suspended 4 μm-diameter superparamagnetic beads above topographically patterned, sputter deposited Ti(4 nm)/Au(60 nm)/[Co(0.7 nm)/Au(1 nm)] × 3 multilayers with perpendicular magnetic anisotropy was investigated. The results impressively demonstrate that the magnetic stray field landscape above the stripe structure when superimposed with an external, slowly rotating, field enables the directed transport of magnetic beads across the stripe panel with velocities up to 12 μm s−1.

The perpendicular exchange bias in NiO(antiferromagnet)/Co(ferromagnet) polycrystalline layer films is studied. It is found that the NiO layer forces the Co layer magnetization to be oriented perpendicular to the film plane in a greater thickness range than is found in the Au/Co/Au system. Simultaneously, a large coercivity and a significant perpendicular exchange bias field were observed that are owing to the interlayer exchange bias coupling between NiO and Co, which supports the perpendicular magnetic anisotropy of the Co layer. These findings are confirmed by magnetometry and magnetoresistance measurements.

Currently, much attention is being paid to patterned multilayer systems in which there exists a perpendicular magnetic anisotropy, because of their potential applications in spintronics devices and in a new generation of magnetic storage media. To further improve their performance, different patterning techniques can be used, which render them suitable also for other applications. Here we show that He(+) 10 keV and Ar(+) 100 keV ion bombardment of (Ni(80)Fe(20)-2 nm/Au-2 nm/Co-0.6 nm/Au-2 nm)(10) multilayers through colloidal mask enables magnetic patterning of regularly arranged cylindrical magnetic domains, with perpendicular anisotropy, embedded in a non-ferromagnetic matrix or in a ferromagnetic matrix with magnetization oriented along the normal. These domains form an almost perfect two-dimensional hexagonal lattice with a submicron period and a large correlation length in a continuous and flat multilayer system. The magnetic anisotropy of these artificial domains remains unaffected by the magnetic patterning process, however the magnetization configuration of such a system depends on the magnetic properties of the matrix. The micromagnetic simulations were used to explain some of the features of the investigated patterned structures.

Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He + ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states. (Some figures in this article are in colour only in the electronic version)

Defined perpendicular anisotropy gradients in the Co sublayers of a $[\mathrm{Co}(0.6\text{ }\text{ }\mathrm{nm})/\mathrm{Au}(2\text{ }\text{ }\mathrm{nm}){]}_{3}$ sputter-deposited multilayer have been introduced by light ion bombardment through a wedged Au stopper layer. Within such a layer system, domain walls between up- and down-magnetized areas are controllably movable by an external perpendicular homogeneous magnetic field. This method and layer system is very promising for a controlled magnetic particle transport within the stray fields of the moving domain walls.

The magnetisation reversal of polycrystalline permalloy/copper multilayers with antiferromagnetic couplingwas measured as a function of temperature. The magnetisation behavior is discussed in the relation to the exstence of ferromagnetic pinholes bridging neighbouring permalloy layers.

Magnetization reversal of perpendicular anisotropy [Co/Au] multilayers patterned into micrometer wide stripes with a coercivity gradient along the stripes was investigated with polar magnetooptical Kerr effect microscopy. 1 mm-long stripes were bombarded with He+ ions of 10 keV energy to induce the gradient. It was shown that short pulses of a magnetic field applied perpendicularly to the sample plane move domain walls between up- and down-magnetized areas in a direction of regions with higher coercivities.

A magnetic multilayer of the structure substrate/Pt-15 nm/Co-0.8 nm/Pt-wedge(0-7 nm)/Co-0.6 nm/Pt-2 nm is characterized by perpendicular anisotropy of both Co layers. For a Pt spacer thickness tPt≤2.6nm, the magnetization reversal of the Co-layers occurs cooperatively, while for larger tPt, it occurs sequentially. The Co-layer with 0.6 nm thickness (CoS) is magnetically softer than the second one (CoH). In the 2.6≤tPt≤3.0 nm range, there are significant changes of the switching field due to a strong gradient of the interlayer coupling. In this region, the magnetization reversal in the CoS layer takes place reversibly by the propagation of a single, straight domain wall. This specific nature of magnetization reversal is explained by a decelerated motion of the domain wall observed both for the direction corresponding to the increasing, as well as decreasing coupling energy.