Magnetic Force Microscopy Study Research Articles

Microwave Field-Induced Changes in Raman Modes and Magnetic Force Images of Antiferromagnetic NiO Films

Effective control of domain walls or magnetic textures in antiferromagnets promises to enable robust, fast, and nonvolatile memories. The lack of net magnetic moment in antiferromagnets implies the need for creative ways to achieve such a manipulation. We conducted a study to investigate changes in magnetic force microscopy (MFM) imaging and in the magnon-related mode in Raman spectroscopy of virgin NiO films under a microwave pump. After MFM and Raman studies were conducted, a combined action of broadband microwave (0.01–20 GHz, power scanned from −20 to 5 dBm) and magnetic field (up to 3 kOe) were applied to virgin epitaxial (111) NiO and (100) NiO films grown on (0001) Al2O3 and (100) MgO substrates, following which the MFM and Raman studies were repeated. We observed a suppression of the magnon-related Raman mode subsequent to the microwave exposure. Based on MFM imaging, this effect appeared to be caused by the suppression of large antiferromagnetic domain walls due to the possible excitation of antiferromagnetic spin oscillations localized within the antiferromagnetic domain walls.

Magnetic force microscopy study of induced magnetism in graphene nanoribbons influenced by magnetic nanoparticles

Nanoscale analysis of magnetic properties of graphene nanoribbons (GNRs) conjugated with magnetic nanoparticles has been studied in this work. The effect of varying concentrations of Fe3O4 and Ni nanoparticles on the magnetic domain structure of GNRs has been investigated using magnetic force microscopy (MFM). A variable external magnetic field was applied to the samples, and an evident variation in the domain structure with a change in the magnetic field was observed. It was found that magnetic properties and the imaged magnetic domain structure are influenced by the concentration of magnetic nanoparticles conjugated with GNRs. The vibrating sample magnetometry (VSM) studies support the nano-domain studies done using MFM such that the trend observed for the saturation magnetization obtained from vibrating sample magnetometry (VSM) matches that of the phase difference obtained using MFM.

Structural, Optical, Electrical and Magnetic properties of 100Mev Ni7+ irradiated Mn doped ZnO thin films

Structural, optical, electrical and magnetic properties of Mn doped ZnO thin films prepared using sol–gel route and modified by 100 MeV Ni7+ Swift Heavy Ion (SHI) irradiation with fluence rate of 1 × 1012 and 1 × 1013 ions/cm2 were studied. X-Ray Diffraction (XRD) studies revealed monophasic films with improved crystallinity after SHI irradiation. Field Emission Scanning Electron Microscopy and Atomic force microscopy indicates increment in grain size with enhanced surface roughness. Enhancement of defect structure such as oxygen vacancies (∼520 nm) and surface defects (∼480 nm) have been studied by Photoluminescence spectroscopy. UV–Vis spectroscopy revealed decrease in band gap and transmission values. SQUID magnetometer and Magnetic Force Microscopy studies provided the clear evidence of ferromagnetic hysteresis curve (Mv/sH) and presence of magnetic contrast in highly irradiated films. Presented results favor the role of SHI irradiation for inducing room temperature ferromagnetism in Mn doped ZnO thin films.

Real-space imaging of magnetic phase transformation in single crystalline Sm–Ca–Sr based manganite compound

Low-temperature-high-magnetic field magnetic force microscopy studies on colossal magnetoresistance material Sm0.5Ca0.25Sr0.25MnO3 have been carried out. These measurements provide real-space visualization of antiferromagnetic–ferromagnetic (AFM–FM) transition on sub-micron length scale and explain the presence of AFM–FM transition in the temperature-dependent magnetization measurements, but the absence of corresponding metal–insulator transition in temperature-dependent resistivity measurements at the low magnetic field. Distribution of transition temperature over the scanned area indicates towards the quench disorder broadening of the first-order magnetic phase transition. It shows that the length scale of chemical inhomogeneity extends over several micrometers.

A Magnetic Force Microscopy Study of Patterned T-Shaped Structures.

The study of patterned magnetic elements that can sustain more than one bit of the information is an important research line for developing new routes in magnetic storage and magnetic logic devices. Previous Monte Carlo studies of T-shaped magnetic nanostructures revealed the equilibrium and evolution of magnetic states that could be found as a result of the strong configurational anisotropy of these systems. In this work, for the first time, such behavior of T-shaped magnetic nanostructures is experimentally studied. In particular, T-shaped Co nanostructures have been produced by electron beam lithography using a single step lift-off process over Si substrates. The existence of four magnetic stable states has been proven by Magnetic Force Microscopy (MFM) and the analysis was complemented by Micromagnetic Simulations. The results confirmed that even for what can be considered large structures, with μm sizes, such four stable magnetic states can be achieved, and therefore two magnetic bits of information can be stored. We also addressed how to write and read those bits.

Interface-induced optical effects in magnetic two- and three-layer films

Multilayer planar nanostructures formed by ferromagnetic and heavy metals can reveal unique properties governed by their composition and geometry. The main role in their formation belongs to the interfacial spin–orbit interaction leading to specific magnetic distributions and behavior at the nanoscale. Here we present a complex analysis of magneto-optical effects in nanolayered films composed of different combinations of cobalt nanolayers with tantalum and platinum ones. Magnetic force microscopy studies confirm inhomogeneous magnetization distribution in Ta,Pt/CoandTa,Pt/Co/Ta,Pt films, which can be described in terms of magnetic ripple domain or chiral structures. Experiments on the Brillouin light scattering directly confirm the appearance of the interface Dzyaloshinskii-Moriya interaction in the studied films, the effect increases with the structural asymmetry. Finally, interface-sensitive second harmonic generation (SHG) reveals odd in magnetic field SHG intensity effect for the longitudinal geometry of the applied dc magnetic field that is absent for homogeneously magnetized structures.

Visualization of the contrasting domain configurations during the melting and reappear-then-melting processes in a manganite film

We report cryogenic magnetic force microscopy studies of anisotropic-strained (La0.8Pr0.2)2/3Ca1/3MnO3/NdGaO3(001) thin films. Real-space magnetic imaging reveals a robust charge-ordered insulating (COI) magnetic phase with a strong relaxation feature. Remarkably, in the first melting and reappear-then-melting processes, the ferromagnetic metallic (FMM) domain configurations differ dramatically, showing a droplet-like and a stripe-like pattern, respectively. These observations illustrate that the FMM nuclei are randomly self-organized distributed in the virgin highly COI-dominant phase separation state recorded after zero field cooling. Regardless of how to reach the saturated FMM state, the anisotropic nature of the long-range strain involves in and dominates to form well-ordered FMM stripes eventually. Our results facilitate the control and manipulation of phase separation morphology at the micrometer scale.

Study of the Properties of Sm–Fe–Co–Ti–H Compounds with ThMn$${}_{\mathbf{12}}$$–Type Structure by Magnetometry, Atomic Force Microscopy, and Magnetic Force Microscopy

The type of magnetocrystalline anisotropy (MCA) of Sm–Fe–Co–Ti alloys and their hydrides with a ThMn $${}_{12}$$ -type structure has been established by magnetometry at room temperature. Using atomic force microscopy (AFM) in combination with magnetic force microscopy (MFM), the state of their surface was studied. The initial SmFe $${}_{11}$$ Ti and SmFe $${}_{5}$$ Co $${}_{6}$$ Ti samples were obtained by argon arc melting. The SmFe $${}_{11}$$ Ti alloy was subjected to a hydrogenation procedure, as a result of which the SmFe $${}_{11}$$ TiH $${}_{0.4}$$ and SmFe $${}_{11}$$ TiH $${}_{1}$$ samples were synthesized. Using AFM and MFM, the features of topography, defects of the investigated surfaces, domain structure, morphology of magnetic inclusions of the initial samples and their hydrides were established. The main magnetic characteristics of the Sm–Fe–Co–Ti–H system obtained using magnetometry have been compared with the results of MFM studies.

Topography dependence of the metamagnetic phase transition in FeRh thin films

The equiatomic alloy FeRh is of great scientific and technological interest due its highly unusual first-order antiferromagnetic (AF) to ferromagnetic (FM) phase transition. Here we report an exploration of the interplay between topography and phase evolution with a comprehensive magnetic force microscopy study of nominal 50 nm thick FeRh thin films and subtractively patterned wires of width 0.2 µm–2 µm. In continuous films where the surface morphology had not been optimised for smoothness, the topographical variation was observed to dominate the distribution of the magnetic transition temperatures and dictates the nucleation and growth of the magnetic phases. This observation was repeated for patterned elements, where the effects of surface morphology were more significant than those of spatial confinement. These results have clear implications for future studies of low-dimensional FeRh films, as surface topography must be considered when analysing and comparing the transition behaviour of FeRh thin films.

Complementary atomic force microscopy and magnetic force microscopy study for the magnetic transition of cobalt clusters onto gold substrates

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.

Origin and tuning of room temperature ferromagnetism and ferroelectricity in double perovskite Y2NiMnO6 nanostructured thin films

This work reports successful fabrication of double perovskite Y2NiMnO6 nanostructured thin films by pulsed laser deposition technique in oxygen and argon gas atmospheres. The Y2NiMnO6 nanostructured thin films exhibit unexpected above room temperature ferromagnetism and ferroelectricity, indicating the coexistence of more than one ferroic interaction in nanostructured Y2NiMnO6. It is found that the dimension of the nanostructures present in the thin films controls both the ferroelectric and magnetic order of Y2NiMnO6 thin films. Studies indicate that the room temperature ferromagnetism and ferroelectricity have similar origin and can be ascribed to the unsaturated surface spins and surface charge polarization, respectively, associated with the surface of the tiny nanostructures, which constitute the whole thin films. Magnetic force microscopy and piezoelectric force microscopy studies confirm the coexistence of the ferromagnetic and ferroelectric domains in the nanostructured films, respectively, at room temperature. This study demonstrates that tailoring of morphology of the nanostructures provides ample opportunity to tune the inherent ferroelectric and magnetic orders of the Y2NiMnO6 nanostructured thin films.

Magnetic Force Microscopy Study of Multiscale Ion-Implanted Platinum in Silica Glass, Recorded by an Ultrafast Two-Wave Mixing Configuration.

This study explores magnetization exhibited by nanoscale platinum-based structures embedded in pure silica plates. A superposition of laser pulses in the samples produced periodic linear arrangements of micro-sized structures. The samples were integrated by PtO2 microstructures (PtOΣs) with dispersed Pt oxide nanoparticles in their surroundings. The characterization of the materials was performed by high transmission electron microscopy studies. Furthermore, topographical and magnetic effects on the sample surfaces were analyzed by atomic force microscopy and magnetic force microscopy, respectively. The magnetic measurements indicated an enhancement in the gradient phase shift and in the gradient force related to the magnetic PtOΣs. The possibility of tuning the magnetic characteristics of the samples through contact with a Nd2Fe14B magnet was demonstrated. This process corresponds to an innovative method for obtaining magnetic PtOΣs induced by laser pulses. Moreover, an increase in the compactness of the silica with platinum-based structures was confirmed by an evaluation of the effective elastic modulus with reference to pure silica. The multimodal magnetic structures studied in this work seem to be candidates for developing high-density magnetic storage media.

Effect of rapid thermal annealing on the structure, microstructure and magnetic properties of Fe thin films

This paper reports the structure, microstructure and magnetic properties of as-deposited and rapid thermal annealed Fe thin films. Rapid thermal annealing was carried out at 550 °C for different time intervals such as 2, 5, 10, 20 and 30 min. The as-deposited and rapid thermal annealed films were found to exhibit A2 type bcc structure. However, microstructural studies indicated formation of Fe–Si phase for the annealed Fe films. Surface roughness estimated from atomic force microscopy studies displayed an increase in surface roughness with increase in annealing time. Room temperature magnetization studies showed a predominant in-plane magnetic anisotropy for all the films. In addition to this presence of strong out-of-plane anisotropy coupled with in-plane magnetization was clearly evidenced from the considerable increase in the out-of-plane coercivity with increase in annealing time. Magnetic force microscopy studies further confirmed the presence of out-of-plane magnetic anisotropy. Magnetic domain imaging studies showed long period band domain patterns with 180° domain wall for the as-deposited film. The band domains were found to get branched with increase in annealing time. From the hysteresis loops and domain imaging studies it was clear that the magnetization reversal is dominated by domain wall motion.

Magnetic Force Microscopy Study of the Effect of Stresses on the Magnetic State of Ni Particles

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.

Magnetic anisotropy and magnetostrictive properties of sputtered Tb–Dy–Fe–Co thin films

Tb–Dy–Fe–Co thin films grown on Si $$\left\langle {100} \right\rangle$$ substrates at different substrate temperatures viz., room temperature, 300, 400 and 500 °C were investigated for structural, microstructural, magnetic and magnetostrictive properties. Grazing incidence X-ray diffraction studies showed presence of amorphous structure for the as-deposited film. Structural studies further indicated formation of (Tb,Dy)2(Fe,Co)17 and Fe–Co phases for the films grown at higher substrate temperatures. Magnetization measurements displayed presence of strong in-plane magnetic anisotropy for all the films. In addition to this, formation of out-of-plane magnetic anisotropy co-existing with in-plane magnetic anisotropy was noticed for the films grown at higher substrate temperatures. Accordingly, magnetic force microscopy studies indicated a strong out-of-plane magnetic contrast for the films grown at higher substrate temperatures. The magnetostriction estimated from tip deflection measurement was found to be negligibly small for the film grown at intermediate temperature viz., 300 °C. However, with subsequent increase in substrate temperatures the magnetostriction was found to increase. The presence of strong out-of-plane magnetic anisotropy co-existing with in-plane components was found to be detrimental for the development of magnetostriction.

How to measure the local Dzyaloshinskii-Moriya Interaction in Skyrmion Thin-Film Multilayers

The current-driven motion of skyrmions in MnSi and FeGe thinned single crystals could be initiated at current densities of the order of 106 A/m2, five orders of magnitude smaller than for magnetic domain walls. The technologically crucial step of replicating these results in thin films has not been successful to-date, but the reasons are not clear. Elucidating them requires analyzing system characteristics at scales of few nm where the key Dzyaloshinskii-Moriya (DM) interactions vary, and doing so in near-application conditions, i.e. in systems at room temperature, capped with additional layers for oxidation protection. In this work’s magnetic force microscopy (MFM) studies of magnetron-sputtered Ir/Co/Pt-multilayers we show skyrmions that are smaller than previously observed, are not circularly symmetric, and are pinned to 50-nm wide areas where the DM interaction is higher than average. This finding matches our measurement of inhomogeneity of the magnetic moment areal density, which amounts to a standard deviation of the Co layer thickness of 0.3 monolayers in our 0.6 nm thick Co layers. This likely originates in small Co layer thickness variation and alloying. These film characteristics must be controlled with greater precision to preclude skyrmion pinning.

Preparation and characterization of sulfonated semi-crystalline poly(arylene ether)s containing 1,4-FBB moiety as proton exchange membrane fuel cells

Sulfonated semi-crystalline poly(arylene ether)s copolymers containing 1,4-bis(4-fluorobenzoyl)benzene (1,4-FBB), with different degrees of sulfonation (DS), were successfully synthesized via direct polycondensation of 3,3’-disulfonate-4,4’-difluorodiphenylsulfone, bisphenol A, and 1,4-bis(4-fluorobenzoyl)benzene, based on aromatic nucleophilic substitution. The different DS values were realized by controlling the quantity of the sulfonated monomer. The effects of DS on the thermal, mechanical, and oxidative stabilities, water uptake, and ion exchange capacity of the membranes were determined. Compared with Nafion 212®, a state-of-the-art proton-conducting membrane, the block copolymer membrane showed well-separated phase morphology and high proton conductivity at different temperatures. The chemical and phase-separated structures of the copolymers were characterized by proton nuclear magnetic resonance spectroscopy and atomic force microscopy studies. The results showed that semi-crystalline copolymer membranes had acceptable mechanical, thermal, electrochemical, and chemical stabilities. All the above-mentioned results indicate that these semi-crystalline copolymer membranes are good candidate materials for proton exchange membranes.

A chemical, crystallographic and magnetic characterisation of individual iron-oxide grains in Hawaiian lavas

Our knowledge on the behaviour of the geomagnetic field through time critically depends on how information of the past state of the field is recorded by, and stored in iron-bearing minerals such as magnetite. For small, single domain grains these processes are described by classical Néel theory, but the magnetic behaviour of larger, pseudo-single domain or multidomain grains, still is enigmatic. Here we present a chemical, crystallographic and magnetic characterisation of three to six individual, large (~3–10 μm) iron-oxide grains from eleven different flows sampled on the Big Island of Hawai’i. These grains were all subjected to a Magnetic Force Microscopy study to characterise their magnetic domain structure; a Microprobe analyses to assess their chemical composition; and a Scanning Electron Microscopy study to identify phases and crystallographic orientations. This comprehensive dataset enables systematic analyses of their magnetic behaviour as function of chemistry and forms the basis for future micromagnetic modelling studies eventually contributing to the development of a fundamental theory of magnetic behaviour in large iron-oxide grains.

Ferromagnetic Fe2O3 nanopatterns prepared using dip-pen lithography

Ferromagnetic Fe2O3 nanorings and nanorods were deposited on an SiO2/Si substrate by dip-pen lithography using an iron nitrate Fe(NO3)3·9H2O solution. Magnetic force microscopy (MFM) studies have shown that ferromagnetic Fe2O3 nanorings and nanorods have in-plane, oriented, and magnetic domain structures. In particular, nanorings have the vortex magnetization state, not the onion state. Their small-size fabrication and stable magnetic properties may suggest future applicability for next-generation magnetic media memory devices.

Magnetic nanocomposites based on phosphorus-containing polymers—structural characterization and thermal analysis

Fabrication of magnetic nanocomposites containing iron oxide nanoparticles formed in situ within a phosphorus-containing polymer matrix as well as its structural characterization and its thermal degradation is reported here. Comparative structural studies of the parent polymer and nanocomposites were performed using FTIR spectroscopy, x-ray diffraction, and atomic force microscopy. The results confirmed the presence of dispersed iron oxide magnetic nanoparticles in the polymer matrix. The formed composite combines the properties of porous polymer carriers and magnetic particles enabling easy separation and reapplication of such polymeric carriers used in, for example, catalysis or environmental remediation. Studies on thermal degradation of the composites revealed that the process proceeds in three stages while a significant influence of the embedded magnetic particles on that process was observed in the first two stages. Magnetic force microscopy studies revealed that nanocomposites and its calcinated form have strong magnetic properties. The obtained results provide a comprehensive characterization of magnetic nanocomposites and the products of their calcination that are important for their possible applications as sorbents (regeneration conditions, processing temperature, disposal, etc).