Search

The discovery of magnetically doped topological insulators (TIs) provides a strong platform for investigating the correlation between long-range ferromagnetic/antiferromagnetic (FM/AFM) ordering and low temperature electron interference phenomena like weak anti-localization (WAL) or weak localization (WL). One such TI material Bi1−xSbx, which has recently been realised as a potential topological material for spintronics, has been studied in the present work. Influence of magnetic doping such as cobalt (Co) and manganese (Mn) in structural, morphological and magneto-transport properties on Bi0.94Sb0.06 nanoparticles has been investigated. The focus was on studying the correlation between magnetic ordering and WAL/WL. In undoped sample for temperatures up to 5K, field dependent magneto resistance (MR) shows a prominent WAL dip around zero field demonstrating the presence of surface states. In both the Co- and Mn-doped samples, the WAL feature is destroyed indicating the absence of time reversal symmetry (TRS) in the system on doping. Interestingly, in the case of 49% manganese (Mn) doping, a clear crossover from WAL to WL has been observed in the MR alongside magnetic ordering and is evident from magnetic force microscopy as well.

Integration of yttrium iron garnet (YIG) with Si can bring new avenues for garnet-based complementary metal-oxide semiconductor compatible devices. Herein, investigations on the morphological, electrical, and magnetic properties of postgrowth annealed YIG thin films grown on Si substrate were systematically performed at nanoscale lateral resolution, employing the variants of atomic force microscopy (AFM) viz., conductive AFM (C-AFM), kelvin probe force microscopy, and magnetic force microscopy (MFM). Scanning electron microscopy analysis has revealed the formation of three different regions with varied crystallinity defined as center, dark, and surrounding matrix. Interestingly, AFM topography has not shown any surface variation of the obtained three different regions. Despite no variation in their surface topography, notable changes occur in their local conductivity, surface potential, and microstructure of their magnetic domains. C-AFM studies have shown the formation of conducting channels with three different resistivity regions. The tunneling current was enhanced nearly 50 times from the dark region (~1 pA) to the center region (~50 pA). MFM image analysis reveals the formation of two different magnetically active domains in the form of circles (-0.3°) distributed in a surrounding matrix (+0.3°) with a steep change in their magnetic phase degree. The formation of circular magnetic domains with highly distinguishable regions has suggested the potential of YIG/Si films for magnetic memory application. This work has shed light on the prospective of YIG/Si films for resistive and magnetic memory applications and fundamental aspects of growth of YIG on nongarnet substrates.

Current magnetic memories are based on writing and reading out the domains with opposite orientation of the magnetization vector. Alternatively, information can be encoded in regions with a different value of the saturation magnetization. The latter approach can be realized in principle with chemical order-disorder transitions in intermetallic alloys. Here, we study such transformations in a thin-film (35 nm) Fe60Al40alloy and demonstrate the formation of periodic magnetic nanostructures (PMNS) on its surface by direct laser interference patterning (DLIP). These PMNS are nonvolatile and detectable by magnetic force microscopy (MFM) at room temperature after DLIP with a single nanosecond pulse. We provide different arguments that the PMNS we observe originate from increasing magnetization in maxima of the interference pattern because of chemical disordering in the atomic lattice of the alloy at temperatures T higher than the critical temperature Tc for the order (B2)-disorder (A2) transition. Theoretically, our simulations of the temporal evolution of a partially ordered state at T > Tc reveal that the disordering rate is significant even below the melting threshold. Experimentally, we find that the PMNS are erasable with standard thermal annealing at T < Tc.

Atomic and magnetic force microscopy were employed in order to investigate the local magnetic state of individual cobalt clusters electrodeposited onto gold electrodes. The analysis indicated that the diameter of the clusters was similar regardless of the potential formation, or growth stage, but the height and surface coverage changed as the potential augmented. Individual examination of the clusters showed that the height determined the magnetic transition from the single to the multi domain state. By using a theoretical single-domain ferromagnetic model in terms of the clusters dimensions, the magnetic exchange constant at different potential voltages was obtained, which was higher than the cobalt bulk value. In addition, a micromagnetic simulation study was employed to validate the experimental results, and it correctly confirmed the experimental magnetic transition. In addition, a fcc crystalline structure and some insights of the clusters growth mechanism on the gold surface were inferred from the results.

The actuation and levitation of air-suspended objects by a magnetic field, due to its noncontact and holonomic manipulation modes, are important technological capabilities for device applications. However, owing to a higher density of conventional ferromagnets or nanoparticle-containing polymers and strong magnetic fields required for actuation, fabricating lightweight materials with a sensitive magnetic response for weight critical applications is challenging. Here, we report ultralight aerogel-based magnets (aero-magnets) comprising assembled ferromagnetic nanomaterials with highly magnetic anisotropy where the magnetic domains can be programmed by external predesigned fields. To demonstrate the breadth of manufacturing methods for this breed of aero-magnet composites, both silica/nanocellulose aerogel hosts and ferromagnetic nanorod/nanoplatelet guests have been explored. Single and double domains with out-of-plane magnetization are programmed into the aero-magnets and characterized by magnetic force microscopy. The levitation and actuation of the aero-magnets are realized while exposed to a small external magnetic field of 11 mT and introduced to a switching circuit. Furthermore, the elastic moduli of the aero-magnets are estimated by dynamic magnetic responses of the ferromagnetic nanoparticles tightly tethered in the aerogel hosts under rapid cyclic fields. These programmable aero-magnets could serve as monolithic magnetic actuator units in the fields of tiny robots and aerospace components.

In this study we investigated the ferroelectric and piezoelectric behaviour of co-sintered magnetoelectric composite fabricated by tape-casting method using Pb(1-x-3y/2)SrxLay(Zrz,Ti(1-z))O3 piezoelectric ceramic with x = 0.06, y = 0.03, z = 0.56 (PSLZT) multilayer and Ni0.6Zn0.4Fe2O4 (NZFO). PSLZT and NZFO powders were prepared by solid state reaction method and respective thick films were fabricated by tape casting method. PSLZT multilayer with Pt inner electrodes were laminated with NZFO and co-sintered at 1060 °C for 2 h to obtain delamination free layered composite. Scanning electron microscopy was employed to analyse the microstructure and interface of the co-sintered multilayer which are crucial for elastic coupling. Micrographs recorded across the cross section of the composites revealed insignificant interdiffusion between the phases. Individual piezoelectric multilayer and magnetoelectric composites were analysed for their ferroelectric behaviour. Piezo Force Microscopy (PFM) and Magnetic Force Microscopy (MFM) were utilized to study the ferroelectric domains and magnetic domains on top surface of PSLZT multilayer and NZFO, respectively in composite structure. Ferroelectric behaviour of PSLZT multilayer - NZFO composite was recorded and compared with 3 layered PSLZT. The values of remanent polarization were found to be 50.6 μC/cm2 and 55 μm/cm2 whereas capacitance at 1 Hz found to be 31.5 nF and 28.9 nF for PSLZT multilayer and PSLZT multilayer – NZFO composite respectively. Piezoelectric coefficient of PSLZT multilayer was found to be 980–1030 pC/N whereas for PSLZT multilayer – NZFO composites it was 1050–1150 pC/N. Magnetoelectric coefficient of 150 mV/cm.Oe was obtained for the same composite structure.

The magnetic properties in two-dimensional van der Waals materials depend sensitively on structure. CrI3, as an example, has been recently demonstrated to exhibit distinct magnetic properties depending on the layer thickness and stacking order. Bulk CrI3 is ferromagnetic (FM) with a Curie temperature of 61 K and a rhombohedral layer stacking, whereas few-layer CrI3 has a layered antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a monoclinic stacking. In this work, we use cryogenic magnetic force microscopy to investigate CrI3 flakes in the intermediate thickness range (25-200 nm) and find that the two types of magnetic orders, hence the stacking orders, can coexist in the same flake with a layer of ∼13 nm at each surface being in the layered AFM phase similar to few-layer CrI3 and the rest in the bulk FM phase. The switching of the bulk moment proceeds through a remnant state with nearly compensated magnetic moment along the c-axis, indicating formation of c-axis domains allowed by a weak interlayer coupling strength in the rhombohedral phase. Our results provide a comprehensive picture on the magnetism in CrI3 and point to the possibility of engineering magnetic heterostructures within the same material.

Contemporary spintronics devices, notably GMR and TMR-sensors with high linear ranges, stand to benefit from large bias fields in excess of 1T that have been observed in exchange-coupled double layers using rare earth-transition metal ferrimagnets as pinning layers. However, before exploiting the strong coupling the reversal process must be understood at the scales of the smallest devices, where it would be effective. Little is known about these processes to-date, owing to the technical difficulty of imaging magnetic structures smaller than 20nm in fields of several Tesla. Here we image the nanoscale magnetic structures of a double layer comprising a polycrystalline Co/Pt-multilayer (Co/Pt) which is strongly exchange-coupled to an amorphous and magnetically-hard ferrimagnetic TbFe alloy layer. High resolution magnetic force microscopy provides snapshots of the magnetic structures along various applied fields between 0 and 7T as the magnetization reversal takes place. In contrast to a magnetization reversa...

The arrays of permalloy particles with shape anisotropy, prepared via microsphere lithography, have been characterized using atomic force microscopy and magnetic force microscopy. The size effect from spherical particles used as the lithographic mask on the magnetization distribution in the produced particles has been investigated. The magnetic force images of particles have been simulated in order to obtain quantitative values. A comparison of shape reproducibility of particles prepared using microsphere lithography and scanning probe lithography is performed as well.

We report on the results of analysis of variation of the magnetic structure of planar permalloy microparticles under the action of mechanical stresses. The particles were formed on glass substrates and had a square shape in the plane of the sample. It is shown that uniaxial mechanical stresses can be detected from the images of such particles obtained using a magnetic force microscope. Depending on the geometrical sizes of particles, we have determined the ranges of stresses for detecting of which such particles can be effectively used.

We analyzed magnetic force microscopy images of the surface of samples cut parallel and perpendicular to the texture created by applying a field in the process of pressing a magnet. The distribution of the linear size (width) of the domains correlates with the distribution of the projection area of grains onto the shear plane in sintered (PrDy)(FeCo)B magnets with radial magnetization and in prismatic (NdDy)(FeCo)B magnets. The effects of grain size and direction of the axes of easy magnetization of grains on the width of the domains, as the main factors controlling the domain structure, are discussed.

International audience; Irradiation of the heterostructure glass/Ta/Pt/GdFeCo/IrMn/Pt by 50 fs ultra-short laser pulses causes local thinning of the film down to~12-30 nm depth. These pits are distinguished by Atomic Force Microscopy (AFM), while their stray magnetic fields were detected by Magnetic Force Microscopy (MFM). The crater was formed due to layer-by-layer evaporation of the material. No sign of melting was found in the vicinity of the crater at subthreshold laser fluence below 12-15 mJ/cm 2 , but exceeding of the threshold caused destruction of the layers. Energy-dispersive X-ray spectroscopy (EDX) revealed depletion of Gd, Fe and Co, responsible for magnetic properties of the subthreshold crater. The amplitude of the local MOKE signal decreased down to 1.7 times in the irradiated area, while thinning of the ferromagnetic layer was 1.1 times. No proportional change of magneti-zation was caused by bias effect of IrMn layer. Decreased elastic modulus was found inside the subthreshold crater in the irradiated areas. Laser engineering of the surface of GdFeCo thin films opens the way for local control of energy balance between magnetic anisotropy, exchange coupling and Zeeman energy and creation of separated sectors for capture, storage and analysis of the ferromagnetic nanoparticles.

In this work, the effects of Cr on the microstructure, physical, and AC magnetic properties of the Ni49Fe51 alloy was studied. In this respect, three series of thin sheets of (Ni49Fe51)100−xCrx (x = 0, 3, and 7 at. pct) alloys with a final thickness of 120 µm were prepared by means of severe cold rolling and an 1150 °C annealing process at H2 atmosphere. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), (200) X-ray pole figure, and magnetic force microscopy (MFM) were employed to study microstructure, texture, and magnetic domain structure of the alloys. The magnetic characteristics of the samples were evaluated using BH-hysteresis loop tracer at a frequency range of 0.5 to 300 Hz. Based on the results obtained, it was shown that the mean magnetic domain width was increased from 1.006 to 1.398 μm for 0 Cr and 7 Cr samples, respectively. Furthermore, the magnitude of the static hysteresis loss increased and the excess and classical eddy current loss decreased for the Cr-added thin sheets.

This paper presents a novel assay of biomarkers consisting of alpha-fetaprotein (AFP) via the measurements of saturation magnetization and magnetic relaxation. The biofunctionalized magnetic nanoparticles (BMNs) were anti-alpha-fetaprotein (antiAFP) coated onto dextran-coated iron oxide nanoparticles, labeled as Fe3O4-antiAFP, and then conjugated with AFP biotargets. After a complete conjugation of AFP and Fe3O4-antiAFP, the BMNs were dried for magnetic measurements. Magnetic nanoparticle images were obtained from magnetic force microscopy with details regarding the transmission electron microscopy images. Findings show that the saturation magnetization $M_{s}$ increases with a rise in the associated AFP concentration and the magnetic relaxation time $\tau $ also shows a rapid increase when the concentration of AFP is lower than 0.2 ppm. Thus, we demonstrate a sensitive platform for detecting biomarkers by characterizing $M_{\mathrm {s}}$ and $\tau $ with a sensitivity limit of 0.03-ppm AFP. The results can be attributed to the interparticle interactions and the Neel motion of magnetic moments in BMNs.

Exchange coupled structures of half metallic ferromagnets, Heusler Alloy (FM), Co2FeAl (CFA) and antiferromagnet (AF), NiO were fabricated by electron beam evaporation technique on n- and p-type Si substrates. These fabricated bilayer structures were further characterized for structural, morphological and magnetic point of views using x-ray diffraction (XRD), atomic/magnetic force microscopy (AFM/MFM) and vibrating sample magnetometer (VSM) techniques. Structural study shows the presence of CFA alloy and NiO phase. Surface morphology shows the granular feature of the top surface with grain size of 200–300 nm due to clustering of smaller grains. Smaller sized magnetic domains have been observed for the structures. Hysteresis behaviour of NiO/CFA/Si structures shows the ferromagnetic behaviour for in-plane orientation with negligible exchange bias whereas a significant exchange bias for out of plane orientation has been observed. The observed result could be understood due to surface roughness and arrangements of spins near the interface of ferromagnetic and anti-ferromagnetic layers.

Radar absorbing materials (RAM) are of strategic importance to shield the targets from getting detected. The wave impedance matching at shield/air interface is an essential condition to absorb most of the incoming radiation which depends on the combination of permittivity, permeability and conductivity of the various components in the composite. Here, we report fabrication of a novel RAM through one port chemical reduction of graphene oxide (GO) in presence of magnetic inclusion of nano-strontium aluminium ferrite SrAl4Fe8O19 (SAF) to make ternary composite films in Poly (Vinylidene) Fluoride (PVDF). Two concentrations with varying ratio of RGO: SAF, 1:1 (RGOSAF11) and 1:2 (RGOSAF21) in PVDF were prepared. The films were tested for RAM properties in transmission line in X-band (8–12 GHz). Morphology using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and Elemental analysis using Energy Dispersive X-Ray Analysis (EDAX) revealed that there was more non-uniformity in the dispersion as well as elemental composition in RGOSAF11 compared to RGOSAF21. This was also reflected in the magnetic studies using vibrating sample magnetometer (VSM) and Magnetic Force Microscopy (MFM). RGO plays a crucial role in not only providing the conductive paths in the EM wave absorption but also in the magnetic domain communication of magnetic entities within the RGO network. This further facilitates the effective trapping of incoming radiation and therefore exhibited shielding effectiveness of more than 40 dB. Study of dielectric properties suggests that this optimized ratio of RGO and SAF in the composite provides perfect opportunity for various effects like interfacial polarization and scattering centres which are responsible for the improved absorption properties. Such material can be an impressive absorption block in emerging EMI shielding technology.

The magnetic characteristics of compact BaFe12O19 powders have been studied by magnetic force microscopy and magnetometry methods. Powders have been obtained by a chemical method. Compaction-induced magnetic anisotropy of the “easy magnetic plane” type has been found. The nature of anisotropy has been discussed.

The effect of strains on ferromagnetic particles has been studied. Arrays of Ni microparticles of different shapes on glass substrates have been fabricated. The magnetic state of the fabricated particles as a function of the degree of glass substrate bending has been investigated. It has been established that the ground state of unbent particles is vortex. It is shown that the substrate bending leads to the transition from the vortex to quasi-homogeneous state.

The effect of deformations on magnetic nanoparticles of elliptic, square, and triangular shapes is simulated. The distribution of the magnetization of such particles is studied as functions of their shapes and applied deformations. A deformation is shown to possibly lead to the formation of new metastable states and also a change in the type of the ground state of a particle. The deformation substantially changes the distribution of the particle magnetization, which can be detected by their MFM contrast.

Nanowires (NWs) consisting of Ni/Cu and Co/Cu alternating layers with a diameter of 100 nm and layer thicknesses varying between 10 and 500 nm are prepared by template synthesis in pores of polymer track-etched membranes. Bath compositions and different regimes for pulsed electrodeposition of NWs are explored. A procedure for electrodeposition of NWs using pulses of equal charge is developed. By diminishing the amount of charge per pulse, initially we manage to lower the layer thickness to 10–15 nm, but further diminishing of charge in pulses leads to the blending of elemental composition of adjacent layers and/or formation of rod–shell nanostructures within the NWs. The coercive force (15–30 mT) and residual magnetization of our layered NWs are determined from magnetization measurements. For NWs with a layer thickness of 50–100 nm, the magnetization curves recorded in the out-of-plane and in-plane geometries are similar in shape and have similar parameters. For NWs with thicker layers (250 and 500 nm), magnetization curves are markedly different due to magnetic anisotropy (an easy magnetization axis emerges longitudinally to NWs) and interference between neighboring NWs. Magnetic force microscopy of isolated NWs identifies that the NWs comprise magnetic regions extending over ~100–150 nm. The NW can be partially remagnetized by applying an external magnetic field (+16 mT) longitudinally.

The magnetic properties of CoPt, CoPd, and FePd thin films with different contents of a ferromagnetic material fabricated by electron beam evaporation have been compared. The micromagnetic structure investigations have shown a decrease in the magnetic domain size with an increase in the Co content in the CoPt and CoPd films, which has been attributed to the presence of two magnetic phases in the films. The magnetooptical studies have shown anomalously large Faraday angles and the absence of Kerr effect in the CoPt films, which make them attractive for application in optics. In the FePd films, the minimum coercivity values have been obtained from the magnetic-field dependences of the magnetization, which has also been related to the magnetic structure features.

The magnetic and structural properties of metallic alpha-Fe magnetic nanoparticles synthesized by electric explosion of wire technique were investigated. As-prepared particles are highly crystalline and present a high saturation magnetization (M-S = 186 +/- 3 emu/g) that is slightly lower than bulk value (M alpha-Fe = 218 emu/g) due to the presence of a very thin non-magnetic FeOx shell, which increases the chemical stability and biocompatibility, making the particles of great interest for a number of applications, including sensing and biomedicine. When the particles are pressed, strong dipole-dipole interactions arise, giving rise to collective ferromagnetic-like behavior observed with magnetic force microscopy, which results in a reduction of the coercivity, thus suggesting that the interparticle interactions can be used as an additional tool to tune the magnetic properties.

In this paper, magnetite (Fe3O4) powders which were obtained by the emulsion method are analyzed to ascertain the structure and mechanism formation of domains in clusters of Fe3O4 nanoparticles. Magnetic force microscopy (MFM) occupies a special niche in the array of techniques which are currently available for imaging magnetic structures of magnetic nanomaterials, yielding high resolution under ambient conditions. The use of MFM in dynamic lift-mode to detect probe–sample interactions from Fe3O4 nanoparticles is reported here to detect and identify the magnetic domains characterization of nanoparticles. The experimental results showed orientation of magnetic domains in the clustering nanoparticles. Finally, an analysis of repulsion and attraction in magnetic field and direction changes of domains formed by magnetite nanoparticles were done. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features.

The curvature in coiled single-walled carbon nanotubes (SWCNTs) rings impacts on their properties relative to straight CNTs, but the availability of such rings is limited. This has been addressed i...

Forest-like BiFeO3 film formed through electrophoretic deposition of a prepared sol over stainless steel mesh, for the first time. The resultant film characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The photo-electrochemical studies show that the current and open circuit potential moved to positive values under visible light. This explained by the fact that BiFeO3 film generates photo-induced electrons and produce photocurrent and photovoltage. Finally, as prepared thin film used for photocatalytic degradation of phenol in a photocatalytic reactor. The morphology has a significant role on the photocatalytic efficiency due to enhance light-harvesting feature and provide multi scattering centers. Forest-like film was included nano-branches with diameter of 100–150 nm that offer pathways to facilitate electron transfer to substrate. In photocatalytic studies, the effect of important parameters such as initial phenol concentration, addition of H2O2, and rotating speed investigated on the photocatalytic efficiency.

The effect of electron beam rapid thermal annealing (ERTA) on the crystallographic, structural, magnetic and magnetocaloric properties of Sr doped M-type barium hexaferrite thin films (Ba1−xSrxFe12O19) deposited with set optimized parameters on silicon (001) substrates were investigated. Amorphous to crystalline phase transitions occurred when the as-deposited thin films were annealed, however crystallinity reduced as a function of Sr concentration. The as-deposited thin films showed uniform grain size and distribution with reduction in grain size as a function of Sr concentration, whereas annealed thin films showed increase in agglomerated structures as a function of Sr concentration. As-deposited thin films with x = 0, 0.05 and 0.1 showed weak ferromagnetic response. Magnetic hysteresis loops and magnetic force microscopy images indicate improved c-axis in-plane magnetization with reduced coercivity for Sr doped thin films and saturation magnetization for thin films subjected to ERTA. The Arrott plots in positive quadrant suggested a typical M-type ferrite behaviour with second-order ferromagnetic phase transitions around the Curie temperature. The entropy changes associated with magnetic phase transitions were determined using magnetization measurements performed in the range of 50–105 K for as-deposited and 65–125 K for ERTA samples under different magnetic fields. The calculated maximum relative cooling power (RCP) of the as-deposited and ERTA thin films are 1941 mJ/cc and 3065 mJ/cc for 50 kOe magnetic fields. This suggests that Ba1−xSrxFe12O19 with x = 1 is a promising candidate for micro and nano magnetic refrigeration systems.

We demonstrate a method for manipulating small ensembles of vortices in multiply-connected superconducting structures. A micron-size magnetic particle attached to the tip of a silicon cantilever is used to locally apply magnetic flux through the superconducting structure. By scanning the tip over the surface of the device, and by utilizing the dynamical coupling between the vortices and the cantilever, a high-resolution spatial map of the different vortex configurations is obtained. Moving the tip to a particular location in the map stabilizes a distinct multi-vortex configuration. Thus, the scanning of the tip over a particular trajectory in space permits non-trivial operations to be performed, such as braiding of individual vortices within a larger vortex ensemble -- a key capability required by many proposals for topological quantum computing., Comment: 14 pages, 9 figures

Recently, spin spiral type multiferroic materials are widely investigated for their unusual properties and potential applications in memory technology, sensors, and field-effect transistors. It is of interest to investigate surface magnetism in iron vanadate (FeV2O4) due to varying physical properties. Here, the temperature-dependent magnetic domain evolution has been systematically investigated by using cryogenic magnetic force microscopy (MFM). We find irregular and asymmetrical magnetic domain coarsening and shrinking as a function of temperature and also different domain evolution between field cooled and zero field cooled MFM. These findings provide an improved understanding of physical properties related to domain structures.

Properties of polycrystalline TiO2 films modified by magnetron sputtering of cobalt followed by pulsed photon-irradiation processing in air are investigated by methods of X-ray phase analysis, raster electron microscopy, atomic force microscopy, magnetic force microscopy, and IR spectroscopy. Formation of a nanocrystalline (with a grain size of ~50 nm) film consisting of cobalt and titanium oxides the surface of which exhibits magnetic properties is established in the process of modification. The IR reflectance spectra obtained at different angles of incidence in the region between 500 and 600 cm–1 reveal the presence of two bands belonging to transverse modes (TO) and two corresponding bands belonging to the longitudinal modes (LO). These bands are indicative of formation of Co3О4 with spinel structure. Investigation of optical absorption suggests a predominant existence of phases characterized by direct interband transitions with energies of 1.43 and 1.83 eV for Co3O4, along with a transition with energy of 2.65 eV for cubic phase of CoO, in the films.

Magnetic force microscopy (MFM) has become a widely used tool for the characterization of magnetic properties. However, the magnetic signal can be overlapped by additional forces acting on the tip such as electrostatic forces. In this work the possibility to reduce capacitive coupling effects between tip and substrate is discussed in relation to the thickness of a dielectric layer introduced in the system. Single superparamagnetic iron oxide nanoparticles (SPIONs) are used as a model system, because their magnetic signal is contrariwise to the signal due to capacitive coupling so that it is possible to distinguish between magnetic and electric force contributions. Introducing a dielectric layer between substrate and nanoparticle the capacitive coupling can be tuned and minimized for thick layers. Using the theory of capacitive coupling and the magnetic point dipole-dipole model we could theoretically explain and experimentally prove the phase signal for single superparamagnetic nanoparticles as a function of the layer thickness of the dielectric layer. Tuning the capacitive coupling by variation of the dielectric layer thickness between nanoparticle and substrate allows the distinction between the electric and the magnetic contributions to the MFM signal. The theory also predicts decreasing topographic effects in MFM signals due to surface roughness of dielectric films with increasing film thickness. The authors acknowledge the financial support by the ELSTATIK-Foundation Gunter and Sylvia Luttgens through the project ESEMA and DAAD through the project MPFL.

Fe78Si9B13 thin films having a controlled weak perpendicular anisotropy resulting in dense stripe domain configuration have been prepared to investigate their rotatable anisotropy properties. Vector vibrating sample magnetometry, an innovative field-dependent magnetic force microscopy, and ferromagnetic resonance techniques have been jointly exploited to correlate the perpendicular anisotropy to the threshold field value that must be overcome to induce the stripes realignment. A linear relationship between these two quantities is found. The presence of the threshold field is attributed to the portions of the samples whose magnetisation must flip its perpendicular component during a rotation process, therefore encountering the energy barrier of the perpendicular anisotropy.

Magnetic force microscopy (MFM) is an atomic force microscopy (AFM)-based technique to map magnetic domains in a sample. MFM is widely used to characterize magnetic recording media, magnetic domain walls in materials, nanoparticles and more recently iron deposits in biological samples. However, conventional MFM requires multiple scans of the samples, suffers from various artifacts and is limited in its capability for multimodal imaging or imaging in a fluid environment. We propose a new modality, namely indirect magnetic force microscopy (ID-MFM), a technique that employs an ultrathin barrier between the probe and the sample. Using fluorescently conjugated superparamagnetic nanoparticles, we demonstrate how ID-MFM can be achieved using commercially available silicon nitride windows, MFM probes and AFM equipment. The MFM signals obtained using ID-MFM were comparable to those obtained using conventional MFM. Further, samples prepared for ID-MFM were compatible with multi-modal imaging via fluorescence and transmission electron microscopy. Thus ID-MFM can serve as a high-throughput, multi-modal microscopy technique which can be especially attractive for detecting magnetism in nanoparticles and biological samples.

Fe3O4 nanoparticles with crystallite sizes around 10 nm were synthesized by an emulsion method. X-ray diffractometer (XRD) shows that nanocrystalline Fe3O4 possesses face center cubic structure. The magnetic characteristics are investigated by magnetic force microscopy (MFM). Magnetic field directions were applied parallel and perpendicular to the Fe3O4 sample surface for magnetic measurements. Under the perpendicular magnetic field, the phase images of most magnetic nanoparticles exhibit bright or dark MFM contrast. In comparison, the parallel field phase images display a bright–dark dipole MFM contrast, with in-plane magnetic domain configurations. Furthermore, the investigation of strip domains inside Fe3O4 particles under altering magnetic fields indicates the existence of magnetic anisotropy energies, dipole energies as well as inter-grain coupling energies inside the clusters. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features.

Skyrmion imaging and electrical detection via topological Hall (TH) effect are two primary techniques for probing magnetic skyrmions, which hold promise for next-generation magnetic storage. However, these two kinds of complementary techniques have rarely been employed to investigate the same samples. We report the observation of nanoscale skyrmions in SrIrO3/SrRuO3 (SIO/SRO) bilayers in a wide temperature range from 10 to 100 K. The SIO/SRO bilayers exhibit a remarkable TH effect, which is up to 200% larger than the anomalous Hall (AH) effect at 5 K, and zero-field TH effect at 90 K. Using variable-temperature, high-field magnetic force microscopy (MFM), we imaged skyrmions as small as 10 nm, which emerge in the same field ranges as the TH effect. These results reveal a rich space for skyrmion exploration and tunability in oxide heterostructures.

A spontaneous vortex structure in magnetic domains (vortex domains) has been visualized by the decoration technique near the ferromagnetic transition temperature (TC = 18 K) in a ferromagnetic superconductor EuFe2(As0.79P0.21)2 single crystal with the superconducting transition temperature (TSC = 22 K). Meissner domains previously observed by magnetic force microscopy have also been observed in a narrow temperature range (ΔT ∼ 1 K) near TC. A domain structure with the alternating direction of the magnetic flux has been observed upon cooling below TC. Experimental results are in reasonable agreement with a theoretical estimate of the periods of domain structures and the temperature interval below TC in which they are observed.

Recent developments in quantum electronics, particularly spin-qubit systems and semiconductor spintronics, provide new applications for micromagnets. The stray field of properly placed micromagnets can be employed to manipulate spin-qubits using rf-signals. Micromagnets are used as the injector and detector contacts in semiconductor spintronics. For both applications, single-domain magnets with precisely known magnetic properties, with and without external field, are required. We report on Fe micromagnets with different aspect ratio, fabricated using standard semiconductor processing technology. We describe a simple setup using a custom-built electromagnet and conventional atomic force microscope to characterize the micromagnets in an external magnetic field using magnetic force microscopy (MFM). We use this setup to characterize the fabricated micromagnets' domain structure and switching behaviour. We show that MFM, together with the custom-built electromagnet is a simple, yet versatile method to characterize micromagnets for applications in quantum electronics. We furthermore show that the fabricated micromagnets all exhibit the desired single-domain state. The micromagnets differ in their coercive field, depending on the aspect ratio. This makes these micromagnets suitable for spin-injection and spin-detection.

We experimentally demonstrate the formation of room-temperature skyrmions with radii of about 25 nm in easy-plane anisotropy multilayers with an interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of individual magnetic skyrmions by magnetic force microscopy and find that the skyrmions are stable in out-of-plane fields up to about 200 mT. We determine the interlayer exchange coupling as well as the strength of the interfacial DMI. Additionally, we investigate the dynamic microwave spin excitations by broadband magnetic resonance spectroscopy. From the uniform Kittel mode we determine the magnetic anisotropy and low damping ${\ensuremath{\alpha}}_{\mathrm{G}}l0.04$. We also find clear magnetic resonance signatures in the nonuniform (skyrmion) state. Our findings demonstrate that skyrmions in easy-plane multilayers are promising for spin-dynamical applications.

High-Entropy Alloys are advanced technological materials composed of several (typically five) elements in nearly equal atomic concentration. By forming these alloys, previously unknown phase fields of multidimensional phase diagrams are explored. The large number of possible substitutions of constituent elements on crystal lattice sites justifies the dominant contribution of mixing entropy over enthalpy to the free energy reduction. This leads to the formation of phases, which otherwise could not be formed in alloys with fewer main alloying elements. Here we explore magnetic and compositional properties of a High-Entropy Alloy, namely FeCoNiAl x Mn x (0.05 ≤ x ≤ 3.08), composed of magnetic (Fe, Co, Ni) and non-magnetic elements (Al, Mn). By magnetic force microscopy of a selected area, it is observed that for intermediate to low Al and Mn contents, the alloy splits in two major crystallographic phases with different magnetic properties. Elemental maps of the same area were recorded with energy dispersive spectroscopy and scanning electron microscopy. Counterintuitively, it was found that the phase rich in non-magnetic Al has stronger magnetism than the phase rich in Fe. This work showcases possible applications of the here presented HEAs as soft magnetic materials in functional magnetic elements.

Exotic spin-dependent interactions may be generated by exchanging hypothetical bosons that have been proposed to solve some mysteries in physics by theories beyond the standard model of particle physics. The search for such interactions can be conducted by tabletop scale experiments using high precision measurement techniques. Here we report an experiment to explore the parity-odd interaction between moving polarized electrons and unpolarized nucleons using a magnetic force microscope. The polarized electrons are provided by the magnetic tip at the end of a silicon cantilever, and their polarizations are approximately magnetized in the plane of the magnetic coating on the tip. A periodic structure with alternative gold and silicon dioxide stripes provides unpolarized nucleons with periodic number density modulation. The exotic forces are expected to change the oscillation amplitude of the cantilever which is measured by a fiber laser interferometer. Data has been taken by scanning the tip over the nucleon source structure at constant separation, and no exotic signal related to the density modulation has been observed. Thus, the experiment sets a limit on the electron-nucleon coupling constant, $g_A^eg_V^N\leq 9\times 10^{-15}$ for 15 $\mu$m $\le \lambda \le$ 180 $\mu$m, using a direct force measurement method., Comment: 9 pages, 7 figures

The magnetic skyrmion, a tiny magnetic texture that holds promise as the next-generation information carrier, has been widely studied in recent years. A fine tunability of skyrmion density is required for its real applications in novel memory and logic devices. Here, we report on the manipulation of skyrmion density at room temperature in a Pt/Co/Ta/MgO system composed of multiple repetitions with perpendicular magnetic anisotropy. N\'eel-type skyrmions are observed by performing Lorentz transmission electron microscopy and magnetic force microscopy. The influence of structure repetition on skyrmions is experimentally investigated and further understood by micromagnetic simulations. The variation of skyrmion density with repetition number is mainly attributed to magnetic anisotropy. Meanwhile, thermal annealing is utilized to regulate the skyrmion density, where skyrmion-related properties exert a competitive effect. Our findings provide alternative means to manipulate skyrmion density, further allowing for optimized engineering of skyrmion-based devices.

The various dynamical implementations of the atomic force microscope have become important nanoscale characterization tools for the development of novel materials and devices. One of the most significant factors affecting all dynamical AFM modalities is the cantilever tip-sample surface interaction force. We have developed a detailed mathematical model of this interaction that includes a quantitative consideration of the nonlinearity of the interaction force as a function of the cantilever tip-sample surface separation distance. The model makes full use of cantilever beam dynamics and the multiply differentiability of the continuous force-separation curve that results in a set of coupled differential equations, Eqs.(14) and (15), for the displacement amplitudes of both the cantilever and the sample surface. The coupled dynamical equations are recast in matrix form and solved by a standard iteration procedure, but space limitations allow only a presentation of the salient features of the procedure. Although the mathematical form of the coupled equations are valid for any vibrational mode, only flexural vibrations of the cantilever and out-of-plane oscillations of the sample surface are considered. We emphasize that Eqs.(14) and (15) are obtained assuming that the cantilever is a rectangular beam of constant cross-section, the dynamics of which are characterized by a set of eigenfunctions that form an orthogonal basis for the solution set. For some other cantilever shape a different orthogonal basis set of eigenfunctions would be appropriate. However, the mathematical procedure used here would lead again to Eqs.(14) and (15) with values of the coefficients appropriate to the different cantilever geometry. Practicably, this means that the shape of the cantilever is not as important in the solution set as knowing the cantilever modal resonant frequencies, obtained experimentally. The modal frequencies and solution set are expanded to include nonlinear modes generated by nonlinear interaction forces or large cantilever drive amplitudes. A general steady state solution of the coupled dynamical equations is found that accounts for the positions of the excitation force (e.g., a piezo-transducer) and the cantilever tip along the length of the cantilever and for the position of the laser probe on the cantilever surface. The solution is applied to two dynamical AFM modalities - resonant difference-frequency atomic force ultrasonic microscopy, and the commonly used amplitude modulation-atomic force microscopy. Image generation and contrast equations are obtained for each of the two A-AFM modalities assuming for expediency that the contrast results only from variations in the sample stiffness constant. Since the sample stiffness constant is related directly to the Young modulus of the sample, the contrast can be expressed in terms of the variation in the Young modulus from point to point as the sample is scanned. We note further the existence of two values of the sample stiffness constant, corresponding to the dominantly attractive and dominantly repulsive regimes of the force-separation curve. The two values allow for a bi-stability in the cantilever oscillations that is experimentally observed. Equations for both the maximum nonlinearity regime and the hard contact (linear) regime of cantilever engagement with the sample surface are obtained. For dynamical AFM operation outside these regimes, it is necessary to use all terms in the solution set given in Section 2 to describe the signal output of a given A-AFM modality. The extent to which the hard contact (linear regime) equations apply depends on how well the approximation F(z 0 ) - holds.

(Bi1−xLax)(Fe,Co)O3 multiferroic magnetic film were fabricated using pulsed DC (direct current) sputtering technique and demonstrated magnetization reversal by applied electric field. The fabricated (Bi0.41La0.59)(Fe0.75Co0.25)O3 films exhibited hysteresis curves of both ferromagnetic and ferroelectric behavior. The saturated magnetization (Ms) of the multiferroic film was about 70 emu/cm3. The squareness (S) (= remanent magnetization (Mr)/Ms) and coercivity (Hc) of perpendicular to film plane are 0.64 and 4.2 kOe which are larger compared with films in parallel to film plane of 0.5 and 2.5 kOe. The electric and magnetic domain structures of the (Bi0.41La0.59)(Fe0.75Co0.25)O3 film analyzed by electric force microscopy (EFM) and magnetic force microscopy (MFM) were clearly induced with submicron scale by applying a local electric field. This magnetization reversal indicates the future realization of high performance magnetic device with low power consumption.

This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

We have developed a theoretical model describing the dynamics of the Josephson vortices in the long planar Josephson junction under the influence of the alternating heterogeneous magnetic field created by the tip of magnetic force microscope (MFM), and external uniform, constant magnetic field. The fitting of the model parameters ensured the coincidence of the calculated dependencies of the junction critical current on the external magnetic field with the experimental data, with a standard deviation of less than 0.1 percent. We considered the range of values of the field corresponding to the penetration of more than 10 Josephson vortices at different positions of the MFM tip. From comparison with the experiment, we obtained the estimates of Josephson length, effective area of the junction, critical current distribution along the junction boundary, inductance of the lead wires of the experimental sample and the distribution of the magnetic flux inside the junction created by the MFM tip.