Magnetic Force Microscopy Research Papers (original) (raw)

2025, Journal de Physique

2025, Physica B-Condensed Matter

Dynamic magnetic susceptibilities of permalloy antidot array film were studied using threedimensional (3D) object oriented micromagnetic framework (OOMMF) code with two dimensional periodic boundary condition (2DPBC) extension. Two major resonance peaks associated with different regions were found in the investigated systems. Both resonance frequencies decrease with increasing inter-hole distance. The frequency corresponding to lower resonance peak increases with increasing film thickness for to 20 nm, and then the resonance frequency varies weakly with the thickness. High frequency resonance peak increases with decreasing inner radius, and disappears when the inner radius is below 10 nm. Low resonance frequency varies from 1.72 to 6.4 GHz when inner radius changes from 5 to 40 nm.

2025, Small

motivated by a broad range of applications for magnetoresistive devices, optical meta-materials, cell-DNA separators, drug delivery vectors, and wave based information transport. Both, the high stability of their magnetic equilibrium state against external perturbations, as well as their robust domain walls, which propagate with velocities faster than the spin wave phase velocity, promote them as appealing candidates for racetrack memory devices and for information transport and processing using spin waves in magnonic applications. Various bottom-up synthesis routes for the preparation of magnetic nanowires exist; including for example electrodeposition based on porous membrane templates and pyrolysis of metal-organic precursors. In particular the pyrolysis of ferrocene allows for the formation of iron-filled carbon nanotubes (FeCNT), i.e., multiwall carbon nanotubes, which contain single-phase single-crystalline iron nanowires, where the body-centered cubic iron phase dominates. Furthermore, iron nanowires with various crystal orientations can be found with no prevalent orientation. The diameters of the carbon nanotubes and the embedded iron nanowires are in the range of 30-100 and 10-40 nm, respectively. The magnetization dynamics of individual Fe-filled multiwall carbonnanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin-wave transport in magnonic applications.

2025, Physical Review Letters

Arrays of suitably patterned and arranged magnetic elements may display artificial spin-ice structures with topological defects in the magnetization, such as Dirac monopoles and Dirac strings. It is known that these defects strongly influence the quasi-static and equilibrium behavior of the spin-ice lattice. Here we study the eigenmode dynamics of such defects in a square lattice consisting of stadium-like thin film elements using micromagnetic simulations. We find that the topological defects display distinct signatures in the mode spectrum, providing a means to qualitatively and quantitatively analyze monopoles and strings which can be measured experimentally.

2025, Journal of Magnetism and Magnetic Materials

The magnetic properties and the magnetization process of electrodeposited thick films of Co-rich CoPt alloys are studied with particular emphasis on the effects of growth rate, controlled by varying the plating current density, and of lateral confinement, analyzing patterned micro-cylinders. We find that varying the plating current density has virtually no effect on the composition of the samples, and hence on the intrinsic magnetic properties, a substantial increase of both coercivity and squareness is obtained when the current is raised. The films are fine-grained, oriented polycrystals with typical grain sizes in the range 50-150 nm, depending on the growth rate. The complex magnetization process is studied in detail by Magnetic Force Microscopy and shown to be governed by interaction domains. It is shown that further improvement of the squareness can be obtained by exploiting the lateral confinement in patterned samples.

2025, Journal of Magnetism and Magnetic Materials

In this contribution it is proven mathematically that it is in principle impossible to determine the magnetic charge distribution inside a magnetic material by a method which measures the stray field outside the sample, such as magnetic force microscopy (MFM). A general source of stray field, E N , is defined and it is shown that different solutions can be found for E N that result in the same stray field. It is also shown how both a perpendicular and a longitudinal medium can be described with the same E N . Using the equations for stray field, resulting from E N , it is also proven that performing the same MFM measurement at different scanning heights does not provide any new information on the stray field for sample; from a measurement at one (constant) height, the stray field at all other heights can be calculated. Moreover, the component of the field parallel to the same plane can be obtained from a measurement of the field component perpendicular to the sample plane.

2025, Nano Letters

Application of carbon nanotubes as reinforcement in structural composites is dependent on the efficient dispersion of the nanotubes in a high performance polymer matrix. The characterization of such dispersion is limited by the lack of available tools to visualize the quality of the matrix/carbon nanotube interaction. The work reported herein demonstrates the use of magnetic force microscopy (MFM) as a promising technique for characterizing the dispersion of nanotubes in a high performance polymer matrix.

2025, Beilstein Journal of Nanotechnology

The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sam...

2025

The American Physical Society 3D ESR-MRI with A Sub-Micrometer Resolution Using Magnetic Resonance Force Microscopy SHIGENORI TSUJI, YOHSUKE YOSHI-NARI, JEOL Ltd. and CREST-JST, Japan, KOSUKE INOMATA, Kyoto Univ. and CREST-JST, Japan -We will present our progress of ESR Magnetic Resonance Force Microscopy (MRFM). In order to improve our previously achieved resolution (2∼3 micrometer), we used an electropolished magnetic tip made of a sintered Nd2Fe14B permanent magnet, which generated a larger magnetic field gradient (8000 T/m) in the very vicinity of the magnetic tip. To avoid a collision between a sample glued on a cantilever and the magnetic tip placed on a 3D stage, the tip-sample direction was set parallel to the cantilever long axis. Magnetic resonance force signals were induced by a cyclic saturation technique. In this setup, the observed signals had an anti-symmetrical phase with respect to a plane that contains a specimen and is perpendicular to the vibrational direction of the cantilever. MRFM image was then reconstructed from the force map through FT deconvolution. At present, our MRFM can produce 3D ESR-MRI with a sub-micrometer spatial resolution.

2025, Applied Physics Letters

We applied the technique of force-detected nuclear magnetic resonance to observe Ga71, Ga69, and As75 in GaAs. The nuclear spin-lattice relaxation time is 21±5 min for Ga69 at ∼5 K and 4.6 T. We have exploited this long relaxation time to first create and then observe spatially varying nuclear spin polarization within the sample, demonstrating a form of contrast for magnetic resonance force microscopy. Such nuclear spin contrast could be used to indirectly image electron spin polarization in GaAs-based spintronic devices.

2025

Nanomagnetic materials are needed for increasing data storage capacity and suited for enhancing the performance of permanent magnets. However, their performance is controlled by magnetic switching, which is driven by a competition between thermal activation energies and anisotropy energies. Here, we elucidate the magnetic switching process in epitaxial films with in-plane and out-of-plane magnetic anisotropies. While in both media the magnetization obeys a logarithmic decay over time, a drastic difference is revealed in their magnetic viscosities. The relaxation logarithmic law is a consequence of the epitaxy itself under which the film growth is initiated through random nucleation followed by islands growth and their coalescence, leading to non-uniform structural domains. These structural domains behave like magnetic domains due to the presence of antiphase boundaries where exchange coupling is disrupted. The activation volume for both media is found to match the average size of the structural domains. The very slow relaxation process under out-of-plane anisotropy is linked to the demagnetizing field, which drastically weakens the irreversible magnetic susceptibility. A simple analytical model was developed and found to well predict and corroborate the experimental findings. This study was conducted on CoFe 2 O 4 films epitaxially grown on (100) and (110) MgO substrates.

2025, Journal of Electrical Engineering

Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM In the paper we present an overview of the latest progress in the conventional lift-mode magnetic force microscopy (MFM) technique, achieved by advanced MFM tips and by lowering the lift height. Although smaller lift height offers improved spatial resolution, we show that lowered tip-sample distance mixes magnetic, atomic and electric forces. We describe an alternative to the lift-mode procedure - Switching Magnetization Magnetic Force Microscopy [SM-MFM], which is based on two-pass scanning in tapping mode AFM with reversed tip magnetization between the scans. We propose design and calculate the magnetic properties of such SM-MFM tips. For best performance the tips must exhibit low magnetic moment, low switching field, and single-domain state at remanence. The switching field of such tips is calculated for Permalloy hexagons.

2025, Journal of Applied Physics

The magnetization dynamics of Co(5 nm)/Ru/Co(5 nm) trilayers with Ru thicknesses from 0.3-0.6 nm is experimentally and theoretically investigated. The coupling between the Co layers is antiferromagnetic (AFM) and yields a stable AFM domain structure with frozen domain walls. Comparing high-resolution magnetic force microscopy (MFM) and pump-probe measurements, we analyze the behavior of the films for different field-strength regimes. For moderate magnetic fields, pump-probe measurements provide dynamic characterization of the coupled precessional modes in the GHz range. The dynamics at small fields is realized by the pinning of AFM domain walls at inhomogeneities. The MFM images yield a domain-wall width that varies from about 150-60 nm. This behavior is explained in terms of a micromagnetic local-anisotropy model.

2025, Jurnal elektrika

This paper presents the review of error correction in 2D shingled magnetic detection. Shingled magnetic recording is one of the techniques proposed in literature for increasing the storage density of magnetic hard disk drive (HDD) due to the number of overwhelming advantages of shingled writing. The success of this technique lies with a proper signal processing and data update approach. In this paper, shingled magnetic recording and two-dimensional magnetic recording has been studied and the current researches done in the two areas has been reviewed with emphasis on elimination of inter-track-interference and inter-symbol-interference. In the reviewed articles studied, a summary was provided on each article depicting the technique adopted and the performance metrics of each of the articles. Summary was provided at the end of the article on the techniques reviewed based on the existing body of knowledge.

2025, Thin Solid Films

The bulk copper ferrite nanomaterials are synthesized by co-precipitation technique. The vibrating sample magnetometer measurement for bulk CuFe 2 O 4 reveals its unsaturated superparamagnetic behavior. The crystallites of the synthesized nanomaterial are in cubic form having an average size of ~100 Å and are used as target to prepare thin films of various thicknesses (600, 900 and 1100 nm) by radio frequency magnetron sputtering technique. X-ray peaks arise only when films are annealed at 1200 °C and also they are found to be in tetragonal structure. The magnetic characteristics of 900 nm unirradiated CuFe 2 O 4 thin film exhibit superparamagnetic behavior and have an unsaturated magnetic moment at high field. Magnetic force microscopy images of unirradiated CuFe 2 O 4 thin films confirm the soft nature of the magnetic materials. The 150 MeV Ni 11+ swift heavy ion irradiation on these thin films at the fluence of 1 × 10 14 ions/cm 2 modifies the polycrystalline nature due to electron-phonon coupling. Atomic force microscopy image shows that the swift heavy ion irradiation induces agglomeration of particles in 600 and 900 nm thin films and increases rms surface roughness from 33.43 to 39.65 and 69.7 to 102.46 nm respectively. However, in 1100 nm film, holes are created and channel-like structures are observed along with a decrease in the rms surface roughness from 75.12 to 24.46 nm. Magnetic force microscopy images of 900 nm irradiated thin film explain the formation of domains on irradiation and are also supported by the ferromagnetic hysteresis observed using vibrating sample magnetometer.

2025, IEEE Transactions on Magnetics

We have experimentally examined the m icr om agn e t i c structure s in C o C r T a/Cr films deposited onto NiP/Al substrates at 25, 100, 150, 200 and 250°C. We prepared all the films in an acerased magnetic state. The Lorentz transmission electron microscopy i m a g e s demonstrate a monotonic decrease of magnetic cluster size with increase of deposition temperature and the magnetic force microscopy results show a decrease of image contrast. This indicates a decrease of intergranular exchange coupling with increase of deposition t e m p e r a t u r e . N a n o p r o b e e n e r g y d i s p e r s i v e spectroscopy (EDS) reveals an increase of Cr segregation at CoCrTa grain boundaries with increase of deposition temperature. The correlation of a n d m i c r o c o ni p os i t i o n a 1 observations supports that Cr segregation at grain boundaries is responsible for decoupling CoCrTa grains. Our nanoprobe EDS results also indicate that the Cr diffuses to the grain boundaries from the inside of the CoCrTa grains as opposed to a diffusion process involving the Cr underlayer. ni i cr o m a gn et i c

2025, Bulletin of the American Physical Society

2025, Journal of Applied Physics

Nanostructures of ferromagnetic oxides having Curie temperatures above room temperature have potential for applications in memory devices and future spin-based electronic applications. In this article, we report on the dc and high frequency magnetic properties of arrays of elliptical CoFe2O4 nanopillars, covering a large area, fabricated by combined electron beam lithography, and a sol-gel based chemical route. The nanopillars were successfully fabricated on insulating oxidized silicon substrates and on epitaxial thin films of ferroelectric BiFeO3. We performed magnetic force microscopy and ferromagnetic resonance spectroscopy on the arrays to probe their magnetic properties. Due to the possible existence of dominant pinning sites, the CoFe2O4 nanopillars are not single-domain even at nanometer size scales.

2025, Applied Physics Letters

We have developed a low-temperature high resolution magnetic force microscope (MFM) using a quartz tuning fork that can operate in a magnetic field. A tuning fork with a spring constant of 1300N∕m mounted with a commercial MFM cantilever tip was used. We have obtained high-resolution images of the stray magnetic fields exerted from grains with a spatial resolution of 15 nm and force resolution of 2 pN at 4.2 K. Tuning fork-based magnetic force microscopes have the potential to be used at millikelvin temperatures due to their low power dissipation and high force sensitivity.

2025, Journal of Magnetism and Magnetic Materials

Static magnetic properties of arrays of micron-size rectangular magnetic permalloy elements are investigated by means of magneto-optic Kerr-effect magnetometry and magnetic force microscopy. The influence of the size and the spacing between the elements on the magnetization curves of the arrays is studied for different orientations of the applied magnetic field. A sizeable magnetic dipole coupling between the elements is found, affecting strongly the magnetic properties of the arrays.

2025, IEEE Transactions on Magnetics

The magnetization reversal process in thin Ndo,lCoo.P films has been observed using a transmission electron microscope equipped with a special attachment to generate a homogeneous magnetic field in the film plane. When the direction of external field is inclined to the uniaxial anisotropy axis the domain structure, low angle NCel walls and rotations of local magnetization direction are asymmetric. An inhomogeneous distribution of the local magnetization direction inside a ferromagnetic film is a source of the stray field. An analysis of domain configuration indicates that the asymmetric low angle NCel walls are charged and produce strong stray fields perpendicular to the domain walls. In the new phase domains the stray field is positive, while in the old phase this field is negative. The local stray fields modify the incoherent rotations as well as the S-W instability and usually oppose the process of incoherent rotation. The local stray field has been calculated in terms of modified Stoner-Wohlfarth model.

2024, arXiv (Cornell University)

Single molecular magnet (SMM) like paramagnetic molecules interacting with the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new system that differs dramatically from the properties of isolated molecules and ferromagnets. However, it is unknown how far deep in the ferromagnetic electrode the impact of the paramagnetic molecule and ferromagnet interactions can travel for various levels of molecular spin states. Our prior experimental studies showed two types of paramagnetic SMMs, the hexanuclear Mn6 and octanuclear Fe-Ni molecular complexes, covalently bonded to ferromagnets produced unprecedented strong antiferromagnetic coupling between two ferromagnets at room temperature leading to a number of intriguing observations. In this paper, we report Monte Carlo Simulations (MCS) study focusing on the impact of the molecular spin state on cross junction shaped MTJ based molecular spintronics device (MTJMSD). Our MCS study focused on the Heisenberg model of MTJMSD and investigated the impact of various molecular coupling strengths, thermal energy, and molecular spin states. To gauge the impact of the molecular spin state on the region of ferromagnetic electrodes, we examined the spatial distribution of molecule-ferromagnet correlated phases. Our MCS study shows that under a strong coupling regime molecular spin state should be ~30% of the ferromagnetic electrode's atomic spins to create long-range correlated phases.

2024, arXiv (Cornell University)

Ability to tailor the nature of the magnetic coupling between two ferromagnetic electrodes can enable the realization of new spintronics device systems. This paper discusses our finding that deposition of an ultrathin tantalum (Ta) on the NiFe top electrode reversed the nature of interferromagnetic electrode coupling. We observed that the deposition of ~ 5 nm Ta on the top of a magnetic tunnel junction with Ta( 2 nm)/Co(5 nm)/NiFe (5 nm)/AlOx( 2 nm)/NiFe (10-15 nm) configuration changed the magnetic coupling between two ferromagnetic electrodes from antiferromagnetic to ferromagnetic. We investigated Ta effect using multiple magnetic characterizations like ferromagnetic resonance, magnetometry, and polarized neutron reflectometry. Ferromagnetic resonance characterization was very sensitive for detecting the changes in magnetic coupling via the insulating spacer. This simple approach of adding Ta film to alter the magnetic coupling can impact the other burgeoning areas like molecular spintronics. We found that preexisting magnetic coupling between two ferromagnetic electrodes impacted the resultant magnetic properties of magnetic tunnel junctions based molecular spintronics devices.

2024, PhDT

OF DISSERTATION FABRICATION AND CHARACTERIZATION OF MOLECULAR SPINTRONICS DEVICES Fabrication of molecular spin devices with ferromagnetic electrodes coupled with a high spin molecule is an important challenge. This doctoral study concentrated on realizing a novel molecular spin device by the bridging of magnetic molecules between two ferromagnetic metal layers of a ferromagnetic-insulator-ferromagnetic tunnel junction on its exposed pattern edges. At the exposed sides, distance between the two metal electrodes is equal to the insulator film thickness; insulator film thickness can be precisely controlled to match the length of a target molecule. Photolithography and thin-film deposition were utilized to produce a series of tunnel junctions based on molecular electrodes of multilayer edge molecular electrodes (MEME) for the first time. In order to make a microscopic tunnel junction with low leakage current to observe the effect of ~10,000 molecules bridged on the exposed edge of a MEME tunnel barrier, growth conditions were optimized; stability of a ~2nm alumina insulator depended on its ability to withstand process-induced mechanical stresses. The conduction mechanism was primarily 1) tunneling from metal electrode to oranometalic core by tunneling through alkane tether that acts as a tunnel barrier 2) rapid electron transfer within the oranometalic Ni-CN-Fe cube and 3) tunneling through alkane tether to the other electrode. Well defined spin-states in the oranometalic Ni-CN-Fe cube would determine electron spin-conduction and possibly provide a mechanism for coupling. MEME with Co/NiFe/AlOx/NiFe configurations exhibited dramatic changes in the transport and magnetic properties after the bridging of oranometalic molecular clusters with S=6 spin state. The molecular cluster produced a strong antiferromagnetic coupling between two ferromagnetic electrodes to the extent, with a lower bound of 20 erg/cm, 2 that properties of individual magnetic layers changed significantly at RT. Magnetization, ferromagnetic resonance and magnetic force microscopy studies were performed. Transport studies of this configuration of MEME exhibited molecule-induced current suppression by ~6 orders by blocking both molecular channels and tunneling between metal leads in the planar 25μm 2 tunnel junction area. A variety of control experiments were performed to validate the current suppression observation, especially critical due to observed corrosion in electrochemical functionalization step. The spin devices were found to be sensitive to light radiation, temperature and magnetic fields. Along with the study of molecular spin devices, several interesting ideas such as ~9% energy efficient ultrathin TaOx based photocell, simplified version of MEME fabrication, and chemical switching were realized. This doctoral study heralds a novel molecular spin device fabrication scheme; these molecular electrodes allow the reliable study of molecular components in molecular transport.

2024, arXiv (Cornell University)

Economical solar energy conversion to electricity can be boosted by the discovery of fundamentally new photovoltaic mechanism, and a suitable system to realize it with commonly available materials like iron (Fe) and nickel (Ni). This paper reports the observation of the photovoltaic effect on a molecular spintronics device, composed of a magnetic tunnel junction (MTJ) and organometallic molecular clusters (OMCs). A prefabricated MTJ with exposed side edges, after enabling the bridging of OMC channels between its two ferromagnetic films, exhibited following phenomenon (i) a dramatic increase in exchange coupling, (ii) 3-6 orders current suppression and (iii) photovoltaic effect. This paper focuses on the photovoltaic effect. Control experiments on isolated ferromagnetic films suggested that OMCs neither affected the magnetic properties nor produced any photovoltaic effect; the photovoltaic effect was only observed on the ferromagnetic films serving as magnetic electrodes in a MTJ. Present paper invites further investigation of the similar photovoltaic effect on other combinations of MTJs and promising magnetic molecules, like single molecular magnets, organometallic clusters, and porphyrins. This research can lead to mass-producible and economical spin photovoltaic devices.

2024, Bulletin of the American Physical Society

Reliable and Versatile Molecular Electrodes PAWAN TYAGI, DONGFENG LI, STEPHEN HOLMES, BRUCE HINDS -Further advancements of molecular electronics will require a reliable and easily scalable electrode fabrication scheme with dimensional control to molecular lengths. We have produced versatile molecular junction (MJ) with high yield ( 90%) long device life (>1year) using simple photolithography and thin film methods. The critical electrode dimension is readily set to the length of a molecule by the thickness of an insulator film at a pattern edge. A variety of MJs were prepared by attaching paramagnetic molecular clusters to span the exposed edge of metal-insulator-metal tunnel junctions. Magnetic (Co, NiFe and Ni) and nonmagnetic (Cu, Pd, Ta and Au) metal electrodes and Al 2 O 3 insulator were utilized. After molecule attachment ∼5000% increase in current over bare tunnel junction current was observed. Control experiments including the use of neat solvents, using junction widths longer than molecules, use of insulating molecules, and the reversible binding of molecule to top electrode confirm the successful fabrication of molecular electrodes. MJs were photoactive producing ∼60mV photo voltage with white light irradiation. Large magneto-resistance effects were seen with magnetic electrodes.

2024, Bulletin of the American Physical Society

Electrodes for Molecular Spin-Valves BRUCE HINDS, PAWAN TYAGI, STEVE HOLMES, University of Kentucky, DONGFENG LI -Realization of spin devices based on the spin-state of magnetic molecules remains a difficult challenge due to the lack of a reliable molecular electrode fabrication process. We have successfully fabricated magnetic Molecular Junctions (MJ's) by having paramagnetic molecular clusters molecules span across the surface of a metal-insulatormetal tunnel junctions (MJT) [Ta/Co/NiFe/Al 2 O 3 (∼2nm)/NiFe] at the exposed cross-junction pattern edge. Interestingly the current from ∼1µA to ∼1nA (RT, 100mV bias) a short time after molecular attachment presumably due to magnetic ordering. Low temperature in-plane magnetization (77 K, 0.4T) further increased magnetic ordering and decreased the junction current to ∼1pA level. Magnetic force microscopy (MFM) spatially showed strong antiferromagnetic coupling between the top and bottom magnetic electrodes. SQIUD-magnetometer study on an array of MJT dots (4um diameter) showed reduction in magnetization after molecular attachment consistent with antiferromagnetic coupling and the dramatic changes in magneto-junction current (uA to pA).

2024, Materials Science Forum

Multilayer edge molecular spintronics device (MEMSD) approach can produce novel logic and memory units for the computers. MEMSD are produced by bridging the molecular channels across the insulator, in the exposed edge region(s) of a magnetic tunnel junction (MTJ). The bridged molecular channels start serving as the dominant exchange coupling medium between the two ferromagnetic electrodes of a MTJ. Present study focus on the effect of molecule enhanced exchange coupling on the magnetic properties of the MTJ. This paper shows that organometallic molecular clusters (OMCs) strongly increased the magnetic coupling between the two ferromagnetic electrodes. SQUID magnetometer showed that OMCs transformed the typical hysteresis magnetization curve of a Co/NiFe/AlOx/NiFe MTJ into linear one. Ferromagnetic resonance studies showed that OMC bridges affected the two fundamental resonance peaks of the Co/NiFe/AlOx/NiFe MTJ. According to magnetic force microscopy, OMCs caused the disappearance of magnetic contrast from the Co/NiFe/AlOx/NiFe tunnel junction area. These three independent and complimentary experiments, suggested the development of extremely strong interlayer exchange coupling. This work delineated a practical route to control the exchange coupling between ferromagnetic electrodes. Ability to tailor magnetic coupling can lead to the development of molecule based quantum computation device architecture. Introduction: Molecular spintronics devices (MSDs) are promising to produce new computer logic and advanced spintronics devices. According to theoretical and experimental studies, MSDs are shown to possess several new remarkable attributes which are not observed with conventional magneto resistance devices. MSDs' development will critically depend on the

2024, Journal of Applied Physics

Nanohole arrays in Ni films have been prepared by a replica/antireplica method based on anodic alumina membranes. The nanohole arrays exhibited long range ordering with hexagonal symmetry, the hole distance was kept constant (105nm), and the hole diameter and the film thickness were varied between 50 and 70nm and 55 and 600nm, respectively. The magnetic domain structures of such samples have been studied by analyzing magnetic force microscopy images at remanent state. Different domain structures have been observed depending on the geometrical characteristics of the films. The experimental results have been interpreted with the help of micromagnetic simulations.

2024, Journal of Applied Physics

Nd-Co amorphous magnetic films with perpendicular magnetic anisotropy have been grown on nanostructured templates prepared with self-organized di-block poly(styrene)-block-poly(4-vinylpyridine) copolymer layers with a periodic structure of 60 nm spaced pores. These templates modify both the magnetic film topography and mechanical strain on a local scale. The effect of these structural changes is particularly noticeable in the low thickness range of the magnetic films where the transition from in-plane to out-of plane magnetization takes place. The Nd-Co films grown on the copolymer template present lower perpendicular magnetic anisotropy and, also, stronger stripe domain pinning effects in comparison with reference films grown on flat Si substrates.

2024, Physica B: Condensed Matter

We have imaged vortices in the conventional superconductors NbSe (crystal) and Nb (thin "lm) with a lowtemperature magnetic force microscope (MFM). The MFM detection is based on commercially available piezoresistive cantilevers. The improved sensitivity (0.2 pN/nm) at 4.3 K has been obtained by using a higher #exural mode of the cantilever. The operation at higher mechanical resonances allows to improve the signal-to-noise ratio by a factor of 3, while limiting the heat dissipation to 50 W. The magnetic tip coating was optimized by relying on Co/Au multilayers grown by molecular beam epitaxy. The possibility to image the Abrikosov vortex lattice in NbSe can be understood in terms of collective pinning e!ects.

2024, Philosophical Magazine

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2024, Philosophical Magazine

The feasibility of accurately measuring the size and the volume fraction of nano-scale plate-shaped precipitates by atomic force microscopy (AFM) has been explored. For quantitative evaluations their unhandy geometry is conveniently described as superellipsoids. The experimental alloy Ni 69 Co 9 Al 18 Ti 4 served as a model system: plate-shaped disordered γ-precipitates form in the L1 2-long-range ordered γ'-matrix. The results obtained by AFM are compared with those derived from transmission (TEM) and from high resolution scanning electron microscopy (SEM). The agreement between the AFM and the TEM results is good. In spite of the low number of SEM images taken, the same holds for Deleted: 8

2024, physica status solidi (RRL) – Rapid Research Letters

Bit‐patterned media at one terabit‐per‐square‐inch (Tb/in2) recording density require a feature size of about 12 nm. The fabrication and characterization of such magnetic nanostructures is still a challenge. In this Letter, we show that magnetic dots can be resolved at 10 nm spacing using magnetic force microscopy (MFM) tips coated with a magnetic film possessing a perpendicular magnetic anisotropy (PMA). Compared to MFM tips with no special magnetic anisotropy, MFM tips with PMA can resolve the bits clearly, because of a smaller magnetic interaction volume, enabling a simple technique for characterizing fine magnetic nanostructures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

2024, Journal of Applied Physics

We report on the use of direct laser interference patterning to form an “anisotropy” lattice in Co∕Pt thin film multilayers. Co∕Pt multilayers have been extensively studied and, for the compositions studied here, are characterized by strong perpendicular magnetic anisotropy in which the magnetic moment is perpendicular to the film plane. In direct laser interference patterning, two-to-four coherent laser beams from a pulsed Nd:YAG laser strike the sample surface simultaneously, and for sufficiently intense beams the sample properties are modified locally where interference maxima occur. Kerr rotation, magnetic force microscopy, and atomic force microscopy measurements after patterning by one pulse from the laser show that the films have a regular array of “dots” with in-plane magnetization in a background matrix of perpendicular magnetization. Such patterning holds promise for the study of model nanoscale magnetic systems.

2024, Elsevier Bv , EngRN Electrical Engineering eJournal, Vol. 7 No. 260,

Note: The tip of a Scanning Tunneling Microscope (STM) or Atomic Force Microscope (AFM) offers not only the ability to image down to atomic resolution, but also the capabilities of nanostructures with such excellent resolution. A paradigmatic example is the fabrication of a furnace furnace by manipulating individual atoms on a surface using STM. Although the speed of making such a thing has recently improved, it is a process with great difficulties in scaling and integrating with the semiconductor industry.

2024, Journal of Electrical Engineering

2024, arXiv (Cornell University)

Although we seriously disagree with many of the points raised in the comment by Edmonds et al. , we feel that it is valuable and timely, since comparison of this comment and our paper 2 serves to underscore an important property of the ferromagnetic semiconductor (Ga,Mn)As in thin film form. In an earlier publication Yu et al. have shown that when the thickness d of a (Ga,Mn)As film is ultra-thin (typically for d < 50 nm), the film will manifest very different stoichiometric and magnetic behavior from bulk (Ga,Mn)As (as represented by specimens with d > 65 nm). As will be seen below, our disagreement with the Comment of Edmonds et al. 1 can largely (although not entirely) be traced to the differences between ultra-thin (Ga,Mn)As films and thicker bulk-like material.

2024, Journal of Magnetism and Magnetic Materials

A detailed study of the magnetization M(H, ¹) of bulk ceramic La Ca MnO (¹ "267 K) in the paramagnetic phase is presented. Near ¹ (¹!¹ (30 K) "rst-order phase transition features are found. At low magnetic "elds (H : 0.3}50 Oe), a sequence of step and plateaus in the e!ective Curie constant C(¹)"M(¹!¹ )/H is found, accompanied by temperature hysteresis. At higher "elds, maxima in dM/dH are found at a characteristic "eld, H (¹), that increases almost linearly with ¹!¹ up to a critical point (¹H +292 K, H +15 kOe). These features agree with the results of the Landau theory of phase transition with negative M coe$cient in the energy expansion (for "rst order). On the other hand, the crossover "eld between the H and classical H magnetoresistance regimes corresponds closely to H (¹) near ¹ but does not reach an end point at least up to 297 K (32 kOe).

2024

In this work an electromagnetic actuator with ferrofluid is investigated. 3D finite element method model is developed and implemented to obtain the distribution of magnetic field in magnetic circuit. Static electromagnetic characteristics of the solenoid type actuator are determined. Electromagnetic force is calculated by Maxwell stress tensor method. Developed model employs the ANSYS 12.1 software package. Results for magnetic field distributions and static electromagnetic characteristics are presented and analysed.

2024, Bulletin of the American Physical Society

Submitted for the SES16 Meeting of The American Physical Society Spin-torque switching in large size nano-magnet with perpendicular magnetic fields. 1 LINQIANG LUO, MEHDI KABIR, STU WOLF, MIRCEA STAN, JIWEI LU, Univ of Virginia-DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co90Fe10/Cu/Ni80Fe20 pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co90Fe10) and free layer (Ni80Fe20) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. The ability to manipulate spin-dynamics on large size devices could prove useful for increasing the output power of the spin-transfer nano-oscillators (STNO).

2024, Journal of Magnetism and Magnetic Materials

The domain con"gurations in permalloy wires (30 nm thick, 1}50 m wide and 210 m long) with a central &bowtie' (10 m long) were investigated in both their demagnetized and remanent states using magnetic force microscopy (MFM) and the results were con"rmed by micromagnetic calculations. Domain walls were found to be trapped at both ends of the bowtie, suggesting that domain-wall trapping is the dominant process in the magnetization reversal of these structures.

2024, Journal of Applied Physics

The domain configuration in permalloy wires ͑30 nm thick, 10 m wide, and 205 m long͒ with a wide size range of a narrow central bridge ͑5 m long and w m wide; 0.5рwр10 m͒ were investigated in both their demagnetized and remanent states using magnetic force microscopy and the results were confirmed by micromagnetic calculations. At the bridge region, domain walls were found to be shifted by a small external field. Scanning magneto-optical Kerr effect revealed that the coercivity in these structures are the same as that in a straight wire, suggesting that domain wall movement is the dominant process in the magnetization reversal of these structures.

2024, Journal of Applied Physics

This article deals with magnetic force microscope images of nanosized domains in Co-coated films made by Pt-coated tips as well as micromagnetic images of data tracks written in recording media. Pt-coated tips have improved image delineation of the magnetic field distribution compared to images obtained by Co-coated hard magnetic tips. The force acting on Pt-coated tips in the magnetic field of the substrate was modeled assuming a paramagnetic tip. Due to the ferromagnetic nature of the interaction between the tip and substrate the spatial resolution of hard magnetic tips was shown to be inadequate to measure details of the features of nanosized domains. A comparison of the magnetic images made by Pt-coated tips with topographic images shows that magnetic domains resist thermal erasure at ambient temperature when they are formed of eight metallic grains.

2024, Physical Review B

Size and orientation effects on the phase coexistence in MnAs/GaAs͑001͒ microribbons were studied using magnetic force microscopy. The magnetostructural phase coexistence reported in MnAs thin films is also observed in the microribbons, even in the smallest ones. However, the stripe array of MnAs films is only preserved in the ribbons confined along the ͓0001͔ direction. Nevertheless, the configuration of the magnetoelastic domains is altered in the ribbons confined along the ͓1120͔ direction. In this last case, the micrometric ribbons exhibit a redistribution of the magnetoelastic phases owed to the relaxation of the epitaxial strains. The results are understood in terms of the anisotropic change in the lattice parameters at the magnetostructural transition.

2024, Thin Solid Films

Investigation and quantifying of the parameters of the phase and structure state, static magnetic properties, magnetic microstructure formed over the entire volume of the film and in the near-surface layer, the surface roughness of Fe(72.4)Ti(5.4)B(19.2)O(3.0) film were carried out using the combination of the methods such as x-ray diffraction, magnetic force microscopy, atomic force microscopy, vibrating-sample magnetometry, and the correlation magnetometry. The Fe(72.4)Ti(5.4)B(19.2)O(3.0) films on glass substrates were produced by magnetron deposition followed by the vacuum annealing at 200 ◦С for 1 h. The interrelation between the investigated parameters was highlighted.

2024

Austenitic and duplex stainless steels contain a mix of austenite and ferrite, with the relative proportions of these phases, and their relative spatial distribution, significantly affecting the engineering properties, thermal ageing behaviour and creep damage accumulation. Given these effects, the ability to map the distribution of phases in a steel at approximately 10 nm resolution or better is of great interest. In these steels the two phases have different magnetic properties since austenite is paramagnetic and ferrite is ferromagnetic so that their distributions can be mapped using magnetic force microscopy (MFM). In this talk we discuss the application of MFM to image and quantify the distribution and proportion of ferrite in SAF 2205 duplex steel and a AISI Type 316H austenitic stainless steel. These results are compared directly with maps recorded in the same regions using the established phase mapping technique of electron back-scatter diffraction (EBSD); including a compar...

2024, Physical Review B

The basic problem of a single hole in a magnetic film with uniaxial anisotropy has been analyzed in detail by magnetic force microscopy, micromagnetic simulations, and an analytical model. The closure magnetization configuration can be described by two −1 / 2 half vortices located at the hole edge along the easy anisotropy axis and confined within a distance L that is determined by the minimization of magnetostatic and anisotropy energies constrained by the magnetic charge conservation within the system.