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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.

We used scanning tunneling microscopy (STM) to study the Cu-induced restructuring of Si(100)-(2 × 1) surface at the atomic scale. Copper was deposited onto silicon substrates kept at room temperature (RT) or 500 °C. Submonolayer amounts of Cu were found to be sufficient to induce a visible restructuring of the Si(100)-(2 × 1) surface manifested by the disappearance of the vacancy line defects (VLDs), as well as dimer rows disordering (for the RT deposition) or the formation of a c(4 × 4) surface reconstruction (for the 500 °C deposition) not reported for the Cu/Si(100) system so far. Higher amounts of Cu deposited onto the RT-disordered surface at 500 °C led to the formation of 3D CuSi crystallites, accompanied by a significant surface roughening. In contrast, deposition of large amounts of Cu onto a pristine Si(100) at 500 °C resulted in the formation of a near-(1 × 1) local surface atoms ordering.

We have measured magnetic damping in polycrystalline Co25Fe75 films adjacent to various nonmagnetic materials (Ti, Cu, Au, NiO) serving as buffer and/or cover layers. It was shown that it is crucial to use a proper buffer layer to achieve low damping in the Co25Fe75 layer. We found that even an ultrathin Cu buffer layer is sufficient to reduce the total damping when inserted between the substrate and the Co25Fe75 layer. The damping measured in the in-plane configuration reduces almost threefold (to α t o t

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.

The ability to induce and control the perpendicular magnetic anisotropy (PMA) of ferromagnetic layers has been widely investigated, especially those that offer additional functionalities (e.g., skyrmion stabilization, voltage-based magnetization switching, rapid propagation of domain walls). Out-of-plane magnetized ferromagnetic layers in direct contact with an oxide belong to this class. Nowadays, investigation of this type of system includes antiferromagnetic oxides (AFOs) because of their potential for new approaches to applied spintronics that exploit the exchange bias (EB) coupling between the ferromagnetic and the AFO layer. Here, we investigate PMA and EB effect in NiO/Co/Au and NiO/Co/NiO layered systems. We show that the coercive and EB fields increase significantly when the Co layer is coupled with two NiO layers, instead of one. Surrounding the Co layer only with NiO layers induces a strong PMA resulting in an out-of-plane magnetized system can be obtained without a heavy metal/ferromagnetic interface. The PMA arises from a significant surface contribution (0.74 mJ/m2) that can be enhanced up to 0.99 mJ/m2 by annealing at moderate temperatures (~450 K). Using field cooling processes for both systems, we demonstrate a wide-ranging control of the exchange bias field without perturbing other magnetic properties of importance.

In this work, we study magnetization switching induced by spin-orbit torque in $\mathrm{W}$ ($\mathrm{Pt}$)/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ heterostructures with variable thickness of $\mathrm{W}$ and $\mathrm{Pt}$ heavy-metal layers, a perpendicularly magnetized $\mathrm{Co}$ layer, and an antiferromagnetic $\mathrm{Ni}\mathrm{O}$ layer. Using current-driven switching and magnetoresistance and anomalous-Hall-effect measurements, we determine the perpendicular and in-plane exchange-bias field. Several Hall-bar devices possessing in-plane exchange bias from both systems are selected and analyzed in relation to our analytical switching model of the critical current density as a function of $\mathrm{Pt}$ and $\mathrm{W}$ thickness, resulting in estimation of the effective spin Hall angle and perpendicular effective magnetic anisotropy. We demonstrate in both the $\mathrm{Pt}$/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ system and the $\mathrm{W}$/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ system deterministic $\mathrm{Co}$ magnetization switching without an external magnetic field, which is replaced by an in-plane exchange-bias field. Moreover, we show that due to a higher effective spin Hall angle in the $\mathrm{W}$-based system than in the $\mathrm{Pt}$-based system, the relative difference between the resistance states in the magnetization current switching to the difference between the resistance states in magnetic field switching determined by the anomalous Hall effect ($\mathrm{\ensuremath{\Delta}}R/\mathrm{\ensuremath{\Delta}}{R}_{\mathrm{AHE}}$) is about twice as high in $\mathrm{W}$-based devices than in $\mathrm{Pt}$-based devices, while the critical switching-current density in $\mathrm{W}$-based devices is 1 order lower than in $\mathrm{Pt}$-based devices. The current-switching stability and the training process are discussed in detail.

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 present experimental data and their theoretical description on spin Hall magnetoresistance (SMR) in bilayers consisting of a heavy metal (H) coupled to in-plane magnetized ferromagnetic metal (F), and determine contributions to the magnetoresistance due to SMR and anisotropic magnetoresistance (AMR) in five different bilayer systems: $$\hbox {W}/\text {Co}_{20}\text {Fe}_{60}\text {B}_{20}$$W/Co20Fe60B20, $$\text {Co}_{20}\text {Fe}_{60}\text {B}_{20}/\hbox {Pt}$$Co20Fe60B20/Pt, $$\hbox {Au}/\text {Co}_{20}\text {Fe}_{60}\text {B}_{20}$$Au/Co20Fe60B20, W/Co, and Co/Pt. The devices used for experiments have different interfacial properties due to either amorphous or crystalline structures of constitutent layers. To determine magnetoresistance contributions and to allow for optimization, the AMR is explicitly included in the diffusion transport equations in the ferromagnets. The results allow determination of different contributions to the magnetoresistance, which can play an important role in optimizing prospective magnetic stray field sensors. They also may be useful in the determination of spin transport properties of metallic magnetic heterostructures in other experiments based on magnetoresistance measurements.

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.

Thin films of SmB 6 were prepared by PLD on several substrates kept at ambient temperature or at 600 ° C during the deposition. As shown, also post-deposition annealing at 600 ° C can be used to obtain good quality SmB 6 , but heating the substrate during deposition results in higher normalized resistance. The highest value R (2 K)/ R (300 K = 2.21 was achieved for the film deposited on a heated, polished ultra-low expansion glass ceramics substrate Clearceram®-Z. Electrical resistance measurements were performed at temperatures from 300 K down to 2 K. Numerical analysis showed that the resistivity can be described by a two-channel model with temperature activated and non-activated terms, while two energy scales were found. Activation energy W A = 3.7 − 4.8 meV, relevant in temperature interval 16 − 22 K, has been attributed to presence of a forbidden gap in SmB 6 and W D = 0.31 − 0.37 meV, which corresponds to the region 2 − 3.3 K is assumed to be a consequence of an impurity band in the forbidden gap.

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.

As spintronics continues its march to replace conventional electronics, spin-orbit-torque (SOT) -induced magnetization switching attracts much attention, due to its relatively low switching current density, and scalability. SOT requires the breaking of time-reversal symmetry, and is typically assisted by an external magnetic field, or additional antiferromagnetic layers in a device. However, this study presents SOT-driven switching $w\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}t$ an external field, in multilayers consisting of two ferromagnetic Co layers with mixed anisotropies, separated by a Pt spacer acting as a source of spin current. This structure has potential in particular for applications in neuromorphic computing.

Magnonic crystals (magnetic metamaterials for manipulating spin waves) are important building blocks for rf filters and logic. However, regular crystals pose significant constraints for complex designs. This study combines time-resolved x-ray microscopy and numerical modeling to show that quasiperiodic Fibonacci crystals provide advanced control of the magnonic band structure. Furthermore, x-ray microscopy yields insight into the quasicrystal's inner workings, and a simple analytical model is derived to facilitate application of these systems.

Magnonic quasicrystals can be used to manipulate spin waves, offering possibilities beyond those of periodic magnonic crystals. The authors investigate one-dimensional magnonic Fibonacci quasicrystals and demonstrate the existence of collective spin waves over a broad range of wave vectors. The spin-wave spectra here are tunable by changing magnetic field amplitude (for continuous band-structure adjustment), magnetization configuration (for reprogrammability), or the dimensions of the elements (for scalability). Beyond being fundamentally interesting, these properties show that magnonic quasicrystals are promising for tomorrow's spintronic, microwave, and magnonic technologies.

The spin Hall effect (SHE) may be used to control the magnetization state of a nanomagnet by exerting spin torque. In a practical system, both spin Hall and interfacial contributions to the torque coexist, making quantitative analysis of SHE difficult. This study uses the dependence of SHE on the thickness of the heavy-metal layer in heterostructures with different combinations of W, Pt, and Co-Fe-B to distinguish the various torque contributions. Both significant interfacial effects and accumulation of spin current in a sandwiched ferromagnet are observed, improving prospects for applications in spintronics.

We investigate experimentally and theoretically the magnetization reversal process in one-dimensional magnonic structures composed of permalloy nanowires of the two different widths and finite length arranged in a periodic and quasiperiodic order. The main features of the hysteresis loop are determined by different shape anisotropies of the component elements and the dipolar interactions between them. We showed, that the dipolar interactions between nanowires forming a ribbon can be controlled by change a distance between the neighboring ribbons. The quasiperiodic order can influence the hysteresis loop by introduction additional tiny switching steps when the dipolar interactions are sufficiently strong., 10 pages, 7 figures

Asymmetric Ir/Co/Pt and Pt/Co/Ir trilayers with a wedged Co layer (Co thickness d = 0 ÷ 3.6 nm) were deposited by magnetron sputtering on naturally oxidized Si substrates with a Ta/Au buffer. Their magnetic properties have been investigated using magneto-optical polar Kerr effect and Brillouin light scattering (BLS) technique in the Damon-Eshbach geometry. The BLS measurements shows a frequency asymmetry between Stokes and anti-Stokes peaks position, exploited to determine interfacial Dzyaloshinskii-Moriya interaction energy density DS. DS was nearly two times larger for the Ir/Co/Pt trilayer than for the Pt/Co/Ir with opposite chirality. The effective uniaxial magnetic anisotropy and Ds depend non-monotonically on d with a maximum at d ≈ 1.2 nm. The asymmetry in linewidth for Stokes and anti-Stokes peaks is observed for both Ir/Co/Pt and Pt/Co/Ir trilayers for d

Laser-induced magnetization dynamics was investigated in Co/Pt/Co trilayer, with 1 nm thick Co-sublayers, as a function of Pt-spacer layer thickness ( d Pt ) using time-resolved magneto-optical Kerr effect. The magnetization precession parameters: frequency (f), amplitude (A) and effective damping parameter ( α eff ) dependencies on the external magnetic field (H) were determined as a function of d Pt . Three different regions of Pt layer thickness: 0–1.3 nm, 1.3–2.5 nm, and 2.5–4 nm, denoted as regions I, II, and III, respectively, exhibiting distinctly different magnetic properties, were distinguished. It is found that as d Pt increases reorientation of Co-magnetizations from in-plane to perpendicular direction occurs at d Pt around 1.2 nm. For d Pt > 2.5 nm magnetization reorientation from parallel to the orthogonal directions due to mixed anisotropies in Co-layers appears. It is found that in the whole d Pt range single magnetization precession frequency occurs, despite different effective magnetic anisotropies of Co-sublayers. Simulation of the magnetization precession parameters was performed in an effective magnetic layer model. We found that the observed A ( H ) behavior is well simulated within the model in region I and III. The α eff ( H ) correlations with A ( H ) in different d Pt regions are discussed.

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.

The determination of the interfacial Dzyaloshinskii-Moriya interaction for perpendicularly magnetized thin layered films is not trivial and therefore needs some experimental efforts to determine its sign and magnitude, especially in the exchange biased system. Here, we developed a method proposed by D.-S. Han et al. [Nano Lett. 16, (2016) 4438], which opens a way to investigate this interaction using a conventional PMOKE magnetometer, also in exchange biased systems. Using our approach we demonstrated that the Au/Co/NiO layered system has a strong negative Dzyaloshinskii-Moriya interaction, which is independent of the direction of perpendicular interlayer exchange bias coupling., Comment: 10 pages, 4 figures

The results of combined (experimental, analytical, and micromagnetic simulations) studies on the evolution of magnetization states and processes in ultrathin films and multilayered systems are presented. We show ways to manipulate magnetization distributions in ultrathin magnetic single or multilayers by tuning: the thickness of the magnetic layer, the thickness of either the non-magnetic cap or spacer layer, the magnetic anisotropy, and the geometrical constrictions of the system. In ultrathin magnetic films, both the magnetization distribution and the critical thickness of the magnetization reorientation phase transition (RPT) between perpendicular and in-plane states can be also controlled by post-growth treatments, e.g., by either ion or light irradiation. By changing the geometrical parameters of the nanostructure, as well as by an applied external magnetic field, one can tune magnetic domain sizes in a giant range (of a few orders of magnitude) and induce the RPT. Transitions between two- and three-dimensional magnetization distributions are discussed.

We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical 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.

Results obtained during examination of the multilayer Co/Au film by different methods of Magnetic Force Microscopy (MFM) are presented. It was shown, that double-pass scanning with MFM tips, characterised by strong magnetic moments resulted in a magnetisation reversal of the sample during MFM imaging. Single pass scanning or use of the MFM tips with low magnetic moments was required to minimise this process. Experimental results demonstrated good correlation between MFM results acquired during single-pass scanning and double-pass scanning with MFM tips characterised by low magnetic moment.

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.

The antiferromagnetically coupled Fe/Si multilayers deposited by magnetron sputtering with different Fe layer thicknesses have been examined. It has been shown that the magnetization of ferromagnetic layer reduces its value with decreasing Fe layers thickness affecting the antiferromagnetic interlayer coupling. This coupling has been found to occur for Fe layer thicker than 0.5 nm. It has been shown that the antiferromagnetic interlayer coupling occurs through the semiconducting spacer layer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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 temperature dependencies of the ferromagnetic resonance (FMR) linewidth and the resonance field-shift have been investigated for NiO/NiFe exchange-biased bilayers from 78 K to 450 K. A broad maximum in the linewidth of 500 Oe, solely due to the exchange-bias, is observed at ≈150 K when the magnetic field is applied along the film plane. When the magnetic field is applied perpendicular to the film plane, the maximum in the linewidth is less pronounced and amounts to 100 Oe at the same temperature. Such a behavior of the FMR linewidth is accompanied with a monotonic increase in the negative resonance field-shift with decreasing temperature. Our results are compared with the previous experimental FMR and Brillouin light scattering data for various ferromagnetic/antiferromagnetic (FM/AF) structures, and suggest that spin dynamics (spin-wave damping and anomalous resonance field-shift) in the FM/AF structures can be described in a consistent way by a single mechanism of the so-called slow-relaxation.

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 Fe/SixFe100-x and Co/Si multilayers have been examined. The strongest antiferromagnetic interlayer coupling, J = -1.94 mJ/m(2), was found in Fe/SixFe100-x multilayers for x = 100. The analysis of the temperature dependences of remanence to saturation magnetization ratios allowed to find the value of semiconductor spacer layer energy gap (E-g approximate to 200 meV) of the examined structures. It suggests that the Fe-Si phase, responsible for antiferromagnetic coupling is an amorphous-like Fe-Si phase. For Co/Si multilayers a very weak exchange coupling and its oscillatory behavior was observed. It was shown that the growth of the Co on Si occurs in an island growth mode. The evolution of magnetic loop shapes can be successfully explained by the interplay between interlayer coupling and anisotropy terms. (C) 2004 Elsevier B.V. All rights reserved.

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.

A key problem in some applications of pseudo spin-valve structures (PSV) is the choice of appropriate materials for soft and hard ferromagnetic layers and their thickness to ensure a high difference in the switching fields. We show that this can be achieved using a NiO/Co structure as a hard magnetic layer. By varying the thickness of the constituent layers, good symmetrical switching characteristics have been shown in PSV structures with NiO/Co as a hard magnetic layer. The most important features of our PSV structures with suitable selected thickness of particular layers are: a relatively high value of GMR amplitude (up to 9% at RT) due to a possible electron specular reflection at the NiO/Co interfaces, a high coercivity (∼500 Oe) of hard magnetic layer resulted from a specific interaction of a 15 nm thick antiferromagnetic NiO with a 2 nm thick Co layer, nearly symmetrical magnetoresistance transfer curves MR(H) due to negligible unidirectional anisotropy field of NiO/Co bilayer with NiO thickness