Magnetic Tip Research Articles

Magnetic force imaging for spatially resolved assessment of ferromagnetic phase fraction in austenitic stainless steel

This paper presents magnetic force imaging (MFI) – a method for spatially resolved quantitative assessment of the ferrite/martensite fraction in austenitic stainless steel or similar materials. This method exploits the force interaction between a magnetic tip and the surface of a specimen, similar to magnetic force microscopy (MFM). It differs from MFM in the size of the tip and close-to-saturation magnetization of the sample under investigation. In this study, AISI 347 (1.4550/ X6CrNiNb18-10) austenitic stainless steel was analyzed in the as-delivered state, i.e., 30 mm diameter round bars. The MFI results show a distinct resemblance of an inhomogeneous structure that forms bands in the rolling direction. This structure retains its initial square cross-section from which the material was hot rolled and has been detected due to the formation of α′-martensite. The information depth of MFI proved to go beyond the depth of α′ formed due to surface preparation only. The material was further characterized by standard methods, including EBSD, EDX, and hardness measurements.

Can magnitip double-J stent serve as a substitute for a standard double-J stent?

To evaluate the morbidity of the magnitip double-J stent (DJ), compare its morbidity to the standard stent, and evaluate the possibility of retrieving the magnetic tip of the DJ stent without cystoscopy. A total of 50 patients having a lower ureteric stone, who underwent uretroscopic stone retrieval and required the use of a DJ, were randomly assigned to 2 groups, each containing 25 patients. Patients in group A were subjected to exploration with a uretroscope and a magnitip DJ while those in group B received a uretroscope and a standard DJ. The morbidity of both types of DJs was assessed by the Arabic version of the ureteral stent symptom questionnaire (USSQ). There was a high level of statistically significant differences between the two groups with regards to the total score of the USSQ, which were higher in group A as compared to group B (126.96±14.76 vs. 98.24±12.9) (p=0.001). Further, the cost of the total procedure was significantly higher in group B (9600±1456.59 vs. 8444±783.73) (p=0.001). No statistically significant difference was found between both groups regarding the application, retrieval accuracy, and discomfort caused by DJ removal. The morbidity caused by the magnetic DJ was found to be higher. However, the removal of the magnetic DJ was less costly than the standard DJ.

Local Josephson vortex generation and manipulation with a Magnetic Force Microscope

Josephson vortices play an essential role in superconducting quantum electronics devices. Often seen as purely conceptual topological objects, 2π-phase singularities, their observation and manipulation are challenging. Here we show that in Superconductor—Normal metal—Superconductor lateral junctions Josephson vortices have a peculiar magnetic fingerprint that we reveal in Magnetic Force Microscopy (MFM) experiments. Based on this discovery, we demonstrate the possibility of the Josephson vortex generation and manipulation by the magnetic tip of a MFM, thus paving a way for the remote inspection and control of individual nano-components of superconducting quantum circuits.

Controlling the nucleation and annihilation of skyrmions with magnetostatic interactions

Skyrmions have become one of the most visited topics during the last decade in condensed matter physics. In this work, and by means of analytical calculations and micromagnetic simulations, we explore the effect of the magnetostatic field generated by a magnetic tip on the stability of skyrmions. Our results show that the interaction energy between the tip and the skyrmion plays a fundamental role in the stabilization of Néel skyrmions confined in nanodisks, allowing its nucleation and annihilation and also providing precise control of its size and polarity. Based on our results, we propose a very simple and cyclic method to nucleate and annihilate skyrmions, as well as to control their polarity and chirality. This proposal could open possibilities for logic devices taking advantage of all the degrees of freedom that skyrmionic textures have.

Magnetic non-contact friction from domain wall dynamics actuated by oscillatory mechanical motion

Magnetic friction is a form of non-contact friction arising from the dissipation of energy in a magnet due to spin reorientation in a magnetic field. In this paper, we study magnetic friction in the context of micromagnetics, using our recent implementation of smooth spring-driven motion (Rissanen and Laurson 2018 Phys. Rev. E 97 053301) to simulate ring-down measurements in two setups where domain wall dynamics is induced by mechanical motion. These include a single thin film with a domain wall in an external field and a setup mimicking a magnetic cantilever tip and substrate, in which the two magnets interact through dipolar interactions. We investigate how various micromagnetic parameters influence the domain wall dynamics actuated by the oscillatory spring-driven mechanical motion and the resulting damping coefficient. Our simulations show that the magnitude of magnetic friction can be comparable to other forms of non-contact friction. For oscillation frequencies lower than those inducing excitations of the internal structure of the domain walls, the damping coefficient is found to be independent of frequency. Hence, our results obtained in the frequency range from 8–112 MHz are expected to be relevant also for typical experimental setups operating in the 100 kHz range.

Surface pinning and triggered unwinding of skyrmions in a cubic chiral magnet

In the cubic chiral magnet Fe$_{1-x}$Co$_{x}$Si a metastable state comprising of topologically nontrivial spin whirls, so-called skyrmions, may be preserved down to low temperatures by means of field cooling the sample. This metastable skyrmion state is energetically separated from the topologically trivial ground state by a considerable potential barrier, a phenomenon also referred to as topological protection. Using magnetic force microscopy on the surface of a bulk crystal, we show that certain positions are preferentially and reproducibly decorated with metastable skyrmions, indicating that surface pinning plays a crucial role. Increasing the magnetic field allows an increasing number of skyrmions to overcome the potential barrier, and hence to transform into the ground state. Most notably, we find that the unwinding of individual skyrmions may be triggered by the magnetic tip itself, however, only when its magnetization is aligned parallel to the external field. This implies that the stray field of the tip is key for locally overcoming the topological protection. Both the control of the position of topologically nontrivial states as well as their creation and annihilation on demand pose important challenges in the context of potential skyrmionic applications.

Tuning the Exchange Bias on a Single Atom from 1mT to 10T.

Shrinking spintronic devices to the nanoscale ultimately requires localized control of individual atomic magnetic moments. At these length scales, the exchange interaction plays important roles, such as in the stabilization of spin-quantization axes, the production of spin frustration, and creation of magnetic ordering. Here, we demonstrate the precise control of the exchange bias experienced by a single atom on a surface, covering an energy range of 4 orders of magnitude. The exchange interaction is continuously tunable from milli-eV to micro-eV by adjusting the separation between a spin-1/2 atom on a surface and the magnetic tip of a scanning tunneling microscope. We seamlessly combine inelastic electron tunneling spectroscopy and electron spin resonance to map out the different energy scales. This control of exchange bias over a wide span of energies provides versatile control of spin states, with applications ranging from precise tuning of quantum state properties, to strong exchange bias for local spin doping. In addition, we show that a time-varying exchange interaction generates a localized ac magnetic field that resonantly drives the surface spin. The static and dynamic control of the exchange interaction at the atomic scale provides a new tool to tune the quantum states of coupled-spin systems.

Magnetic force microscopic analysis and the magnetoelectric sensor of PLZT – Spinel ferrite composite films

Abstract Composite films of Pb0.93La0.07Zr0.6Ti0.4O3 (PLZT) with spinel ferrites viz. Ni0.6Zn0.4Fe2O4 (NZFO), Co1.1Mn0.1Fe1.8O4 (CMFO), and Co0.9Zn0.1Fe2O4 (CZFO) respectively, were synthesized by the sol-gel spin coating technique. The layered structure of PLZT and spinel ferrite has been deposited onto silicon (1 1 1) substrate. X-ray diffraction analysis was used to confirm the formation of required phases in the light of JCPDS data. Microstructural investigation carried out using Magnetic Force Microscopy (MFM) operated topography mode depicts presence of grains having size of about 20–25 nm. The dielectric properties of the samples under investigation were recorded in the wide range of temperature measurements, in order to confirm existence of well grown ferroelectric phase and understand phase transition behavior. The magnetoelectric interactions have been investigated using phase signal of Magnetic Force Microscopy (MFM). Variation of MFM phase contrast and phase angle have been investigated as a function of electric field applied between magnetic tip and substrate, which gives an idea about nature of magnetoelectric interactions. The change in the magnetic domain as a function of applied electric field has been used to understand the magnetoelectric interactions present in the layered thin films of PLZT and spinel ferrite composite structure. Maximum phase angle change of 80°, 100° and 18° has been observed in the composite films of PLZT-NZFO, PLZT-CMFO and PLZT-CZFO respectively in presence of the applied voltage of 5 V/−5 V with respect to 0 V. Maximum value of magnetoelectric coefficient estimated for composite films of PLZT and NZFO composite was found to be 98 mV/cm Oe amongst the sample under investigation.

In situ real-time annealing of ultrathin vertical Fe nanowires grown by focused electron beam induced deposition

Focused Electron Beam Induced Deposition is a consolidated technique for the growth of three-dimensional (3D) nanostructures. However, this single-step nanofabrication method requires further efforts to optimize simultaneously dimensional and compositional properties, in particular for deposits with a high aspect ratio. More specifically, ferromagnetic 3D nanowires (NWs) with diameters in the sub-50 nm regime and high metallic contents up to 95 at. % attract great interest to improve the final performance of magnetic nanodevices such as magnetic tips for scanning probe microscopy. In this work, we report on real-time monitoring during chemical purification and structural crystallization processes of ultra-narrow 3D Fe NWs (<50 nm in diameter achieved) by post-growth in situ annealing in a transmission electron microscope. NW heating up to 700 °C in very high vacuum reveals the local increase of the metallic content along the entire NW length concomitant with the growth of large Fe single crystals from initially amorphous compounds. A metallic purity of 95 at. % is observed in several regions, dramatically boosting the initial Fe content of 40 at. %. The real-time in situ tracking of 3D nanostructures during thermal annealing is a key element to design and optimize novel purification processes for the fabrication of customized components to be integrated in spintronic, logic and sensing devices.

Use of a magnetic double J stent in pediatric patients: A case–control study at two Canadian pediatric centers

BackgroundUreteral stents with magnetic tips (Blackstar©) were recently approved for use in Canada. To our knowledge this is the first published evidence of their use in pediatric patients. Traditionally, pediatric stent insertion and removal are performed under general anesthetic. Magnetic stents have three main benefits in pediatric patients; cost savings, decreased OR time and reduced general anesthetic exposure. MethodsThis study was a proof of concept pilot, ran from May 2017–May 2018 to demonstrate the safety and efficacy of magnetic stents in pediatric patients. Patients undergoing ureteroscopy, ureteric re-implantation, and pyeloplasty with simultaneous magnetic stent insertion. Forty (40) patients had regular double J stents removed under anesthesia and served as control cases, and 40 patients had a magnetic double J at initial surgery at two different sites, CHU de Quebec and Alberta Children's Hospital. ResultsOverall, 39 magnetic stents were successfully retrieved without general anesthetic, representing a retrieval failure rate of only 2.5%. ConclusionAs demonstrated in our research, magnetic stents represent a safe and equally effective alternative to traditional stents, especially in a pediatric patient. This is because, at worst, if retrieval of the magnetic stent fails, traditional cystoscopic removal can be performed, so nothing is lost. Study TypeCase–control study. Level of evidenceLevel III.

An innovative micro magnetic separator based on 3D micro-copper-coil exciting soft magnetic tips and FeNi wires for bio-target sorting

Manipulation of cells or bio-targets is required in a variety of biological, diagnostic and therapeutic applications. In this paper, we present a novel magnetic separator for magnetic bead labeled-target sorting in microfluidic systems. This micro magnetic separator includes 3D micro copper coil, soft magnetic tips and FeNi wires. The magnetic tips and FeNi wires are first simulated and optimized by MagNet software to increase the magnetic force exerted on magnetic beads, and fabricated by microfabrication technology. The experiment results show the sorting ratio of the magnetic beads can be up to 92.5% with the current of 200 mA and the flow rate of 5 µL/min. The maximum sorting ratio can reach 78.4% for 100 CFU/mL E. coli O157:H7 sample with the current of 200 mA and the flow rate of 0.5 µL/min. On account of the miniaturization, high sorting efficiency, low excitation current, high level of detection automation and easy integration with micro magnetic sensor, this micro magnetic separation system can be a potential application in bio-target sorting and detecting.

Simulation study of the influence of leak electrons on the discharge characteristics of a cusped field thruster

Previous studies have shown that leak electrons in cusped field thrusters can move along the channel axis to the anode after crossing the magnetic cusp on the exit. In this paper, a one-dimensional fluid model is built along two typical electron paths to study the influence of leak electrons on the discharge characteristics of a cusped field thruster, considering the electron temperature equation. It is found that the frequencies of low-frequency oscillations increase with a decrease in the proportion of leak electrons, which is related to an increase in the ion speed in the channel. Simulation results show that the position of the peak electron temperature is near the magnetic cusp on the exit and the position of the peak electron density is located downstream from the middle magnetic tip. With a decrease in the proportion of the leak electrons, the peak electron temperature and peak electron density decrease and the position of the peak electron density moves away from the exit, which is related to a decrease in the potential fall on the exit and an increase in confinement of electrons to the middle magnetic cusp.

A parametric resonator with low threshold excitation for vibration energy harvesting

A parametric resonator for vibration energy harvesting is presented. Despite large responses from parametric resonance, two major drawbacks of parametric resonance harvesters are the high threshold excitation and narrow bandwidth. We addressed these two shortcomings by adding magnetic nonlinearity to the system. The proposed vibration energy harvester consists of two piezoelectric cantilevers beams, each with a magnetic tip. By controlling the distance between the two magnets, the threshold excitation level needed to trigger the parametric resonance decreases. Combining the softening and hardening behavior of the two magnetically coupled beams increases the frequency bandwidth. In addition, the amplitude of the response increases with the merger of the direct and parametric resonances of the two beams. We present a mathematical model of the system consisting of two lumped systems coupled by the magnetic force. The coupled governing equations are solved numerically, analytically, and are verified by experiments. Unique characteristics of wider bandwidth, larger response, and lower threshold excitation occur at the low frequency because of the added magnetic nonlinearity to the two-beam system. These properties can improve the efficiency of vibration energy harvesters.

Magnetic Force Sensing Using a Self-Assembled Nanowire.

We present a scanning magnetic force sensor based on an individual magnet-tipped GaAs nanowire (NW) grown by molecular beam epitaxy. Its magnetic tip consists of a final segment of single-crystal MnAs formed by sequential crystallization of the liquid Ga catalyst droplet. We characterize the mechanical and magnetic properties of such NWs by measuring their flexural mechanical response in an applied magnetic field. Comparison with numerical simulations allows the identification of their equilibrium magnetization configurations, which in some cases include magnetic vortices. To determine a NW's performance as a magnetic scanning probe, we measure its response to the field profile of a lithographically patterned current-carrying wire. The NWs' tiny tips and their high force sensitivity make them promising for imaging weak magnetic field patterns on the nanometer-scale, as required for mapping mesoscopic transport and spin textures or in nanometer-scale magnetic resonance.

Breathers and other time-periodic solutions in an array of cantilevers decorated with magnets

In this article, the existence, stability and bifurcation structure of time-periodic solutions (including ones that also have the property of spatial localization, i.e., breathers) are studied in an array of cantilevers that have magnetic tips. The repelling magnetic tips are responsible for the intersite nonlinearity of the system, whereas the cantilevers are responsible for the onsite (potentially nonlinear) force. The relevant model is of the mixed Fermi-Pasta-Ulam-Tsingou and Klein-Gordon type with both damping and driving. In the case of base excitation, we provide experimental results to validate the model. In particular, we identify regions of bistability in the model and in the experiment, which agree with minimal tuning of the system parameters. We carry out additional numerical explorations in order to contrast the base excitation problem with the boundary excitation problem and the problem with a single mass defect. We find that the base excitation problem is more stable than the boundary excitation problem and that breathers are possible in the defect system. The effect of an onsite nonlinearity is also considered, where it is shown that bistability is possible for both softening and hardening cubic nonlinearities.

In Situ Real-Time Annealing of Ultrathin Vertical Fe Nanowires Grown by Focused Electron Beam Induced Deposition

Focused Electron Beam Induced Deposition is a consolidated technique for the growth ofthree-dimensional (3D) nanostructures. However, this single-step nanofabricationmethod requires further efforts to optimize simultaneously dimensional andcompositional properties, in particular for deposits with a high aspect ratio. Morespecifically, ferromagnetic 3D nanowires (NWs) with diameters in the sub-50 nm regimeand high metallic contents up to 95 at. % attract great interest to improve the finalperformance of magnetic nanodevices such as magnetic tips for scanning probemicroscopy. In this work, we report on real-time monitoring during chemical purificationand structural crystallization processes of ultra-narrow 3D Fe NWs (<50 nm in diameterachieved) by post-growth in situ annealing in a transmission electron microscope. NWheating up to 700 oC in very high vacuum reveals the local increase of the metallic contentalong the entire NW length concomitant with the growth of large Fe single crystals frominitially amorphous compounds. A metallic purity of 95 at. % is observed in severalregions, dramatically boosting the initial Fe content of 40 at. %. The real-time in situtracking of 3D nanostructures during thermal annealing is a key element to design andoptimize novel purification processes for the fabrication of customized components to beintegrated in spintronic, logic and sensing devices.

Poling of an artificial magneto-toroidal crystal.

Although ferromagnetism is known to be of enormous importance, the exploitation of materials with a compensated (for example, antiferromagnetic) arrangement of long-range ordered magnetic moments is still in its infancy. Antiferromagnetism is more robust against external perturbations, exhibits ultrafast responses of the spin system1 and is key to phenomena such as exchange bias2,3, magnetically induced ferroelectricity4 or certain magnetoresistance phenomena5. However, there is no conjugate field for the manipulation of antiferromagnetic order, hindering both its observation and direct manipulation. Only recently, direct poling of a particular antiferromagnet was achieved with spintronic approaches6. An interesting alternative to antiferromagnetism is ferrotoroidicity-a recently established fourth form of ferroic order7,8. This is defined as a vortex-like magnetic state with zero net magnetization, yet with a spontaneously occurring toroidal moment9. As a hallmark of ferroic order, there must be a conjugate field that can manipulate the order parameter. For ferrotoroidic materials, this is a toroidal field-a magnetic vortex field violating both space-inversion and time-reversal symmetry analogous to the toroidal moment10. However, the nature and generation of the toroidal field remain elusive for conventional crystalline systems. Here, we demonstrate the creation of an artificial crystal11,12 consisting of mesoscopic planar nanomagnets with a magneto-toroidal-ordered ground state. Effective toroidal fields of either sign are applied by scanning a magnetic tip over the crystal. Thus, we achieve local control over the orientation of the toroidal moment despite its zero net magnetization.

Magnetization characterization of MnAs nanoclusters at close range in bended MnAs/InAs heterojunction nanowires

The authors report on the magnetization and magnetic domains of ferromagnetic MnAs nanoclusters located at relatively close range in a bended MnAs/InAs heterojunction nanowire, which are occasionally observed in the nanowires with multiple MnAs nanoclusters, on the basis of the structural and magnetization characterization results. The magnetization of MnAs nanoclusters is oriented along the external magnetic field directions, in particular, in the case of MnAs nanoclusters formed in the almost straight (or slightly bending) heterojunction nanowires. However, the magnetization of a MnAs nanocluster at the markedly bending position of heterojunction nanowires is occasionally directed by the magnetic force microscope tip magnetization. The decrease in the coercivity of nanoclusters may affect the magnetization directions of nanoclusters at the bending position of heterojunction nanowires.

Wireless power transfer system with center-clamped magneto-mechano-electric (MME) receiver: model validation and efficiency investigation

This paper presents a complete equivalent circuit model for a wireless power transfer concept utilizing a center-clamped piezoelectric cantilever beam with magnetic tip masses as a receiver. The analytical solution for the power delivered to a load resistance is given as a function of material properties, beam characteristics and external magnetic field strength. The lumped element model is experimentally verified. The efficiency of the system is thoroughly investigated and validated. The essential effect of the coil resistance is highlighted. The analyses show that optimization of transmitter coil size and geometry of the piezoelectric transducer has a significant impact on the transduction factor between the magnetic-mechanical-electrical domains, which greatly improves the transmission efficiency. Finally, the model for evaluating the efficiency is generalized for other similar structures.

NanoSQUID Magnetometry on Individual As-grown and Annealed Co Nanowires at Variable Temperature.

Performing magnetization studies on individual nanoparticles is a highly demanding task, especially when measurements need to be carried out under large sweeping magnetic fields or variable temperature. Yet, characterization under varying ambient conditions is paramount in order to fully understand the magnetic behavior of these objects, e.g., the formation of nonuniform states or the mechanisms leading to magnetization reversal and thermal stability. This, in turn, is necessary for the integration of magnetic nanoparticles and nanowires into useful devices, e.g., spin-valves, racetrack memories, or magnetic tip probes. Here, we show that nanosuperconducting quantum interference devices based on high critical temperature superconductors are particularly well suited for this task. We have successfully characterized a number of individual Co nanowires grown through focused electron beam induced deposition and subsequently annealed at different temperatures. Magnetization measurements performed under sweeping magnetic fields (up to ∼100 mT) and variable temperature (1.4-80 K) underscore the intrinsic structural and chemical differences between these nanowires. These point to significant changes in the crystalline structure and the resulting effective magnetic anisotropy of the nanowires, and to the nucleation and subsequent vanishing of antiferromagnetic species within the nanowires annealed at different temperatures.