Field Magnetic Imaging Research Articles

30 T scanning tunnelling microscope in a hybrid magnet with essentially non-metallic design

We report on the construction and performance of the first hybrid resistive-superconducting magnet (HM) based scanning tunnelling microscope (STM) above 30 T. This custom-design HM-STM features a novel design of the STM head unit, whose tip-sample approach is implemented using a slender piezoelectric tube (PZT). The scanner shares part of PZT by fixing a sapphire frame onto the front quarter of PZT to construct a compact tip-sample loop, realising an outer diameter of 8.8 mm, which makes it compatible with a narrow sample space. Its main components are made of non-metallic materials of sapphire, which allows it to be immune from eddy currents and to operate under the condition of strong magnetic field fluctuation from a hybrid magnet, as well as cryogen-free cryocooler magnet systems. To analyse the stiffness of the STM head unit, the eigenfrequencies with 11 kHz and 12 kHz in bending modes, 25 kHz in a torsional mode, and 67 kHz in a longitudinal mode were simulated by finite element analysis; also, the drifting rates of the STM in ambient conditions in the X-Y plane and Z direction were measured at 25.5 and 38.2 pm/min, respectively. We present the first atomic images in magnetic fields up to 30.1 T in an HM. The raw data show the stable and distinguished performance while ramping up to maximum fields, indicating the new device's potential capability of operating in the future 45T-hybrid magnet and hundred-field pulsed magnet. Meanwhile, our compact and concentric cylindrical STM insert can operate in the low-temperature tubular sample space housed by the HM bore to develop low-temperature and extreme high-magnetic field STM.

Microcontroller-based magnetometer using a single nitrogen-vacancy defect in a nanodiamond

The measurement of magnetic properties of various physical systems with nanometric spatial resolution raises interest in areas such as materials science, biotechnology, and information storage and processing. In the present work, a microcontroller-based magnetometer was built using a single nitrogen-vacancy defect in a nanodiamond. The implemented nanomagnetometry method is simple and relies on the frequency modulation of the nitrogen-vacancy defect electron spin resonance using square pulses of an externally applied magnetic field and employs a single microwave source. The developed system has a reasonable sensitivity of 4 μT/Hz and is able to measure magnetic field variations at a rate of around 4 mT/s. This system was used for nanoimaging the inhomogeneous spatial magnetic field profile of a magnetized steel microwire, and a spatial magnetic field gradient of 13 μT/63 nm was measured. Besides its usefulness in nanoscale imaging of magnetic fields, the present work can be of interest in the development of compact nanodiamond based magnetometers.

Imaging stress and magnetism at high pressures using a nanoscale quantum sensor.

Pressure alters the physical, chemical, and electronic properties of matter. The diamond anvil cell enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena. Here, we introduce and use a nanoscale sensing platform that integrates nitrogen-vacancy (NV) color centers directly into the culet of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging of both stress fields and magnetism as a function of pressure and temperature. We quantify all normal and shear stress components and demonstrate vector magnetic field imaging, enabling measurement of the pressure-driven [Formula: see text] phase transition in iron and the complex pressure-temperature phase diagram of gadolinium. A complementary NV-sensing modality using noise spectroscopy enables the characterization of phase transitions even in the absence of static magnetic signatures.

Hysteretic Interference of Time-Overlapping Magnetic Field Pulses

We present calculations of the dependences of the electric voltage $$U\left( H \right)$$ across a magnetic field transducer, scanning a magnetic medium with residual magnetic fields, on the magnetic field strength. The ascending and descending branches of the hysteresis dependences $$U\left( H \right)$$ are described by arctangent functions. The distributions of the electric voltage $$U{\kern 1pt} \left( x \right)$$ over the distance $$x$$ to the projection of the axis of a linear source of pulsed magnetic field onto the magnetic carrier are also presented. Based on the resulting distributions, optical images of residual magnetic fields are formed. The distributions $$U{\kern 1pt} \left( x \right)$$ are produced for magnetic field pulses overlapping in time and delayed relative to each other. It is shown that the results obtained make it possible to increase the sensitivity of measurements and the accuracy of thickness gaging and determining parameters of discontinuities in electrically conductive objects.

The influence of leakage magnetic slit on imaging performance of framing camera

A pulse-dilation framing camera is designed using a combination of magnetic lenses. The axial magnetic field distribution, electronic trajectory and imaging distribution on the object plane are simulated, and the influence of leakage magnetic slit on imaging performance of camera is analyzed. Results show that increasing the leakage magnetic slit improves the imaging performance away from axial area. At an acceleration energy of 3keV, the width of magnetic slit increases from 10 to 70mm, the relative imaging dispersion degree between on-axis and off-axis decreases from 0.27 to 0.06, and the relative mean deflection angle decreases from 65.17° to 59.44°. These features contribute towards further optimization of structural parameters of the magnetic lens and provide design guidelines for achieving a pulse-dilation framing camera with better imaging performance.

Quality evaluation of solar magnetic field images at EUV wavelengths in digital image correlation method

Quality evaluation of solar magnetic field images at EUV wavelengths in digital image correlation method

Real time observation of a stationary magneton

The magnetic dipole field geometry of subatomic elementary particles like the electron differs from the classical macroscopic field imprint of a bar magnet. It resembles more like an eight figure or else joint double quantum-dots instead of the classical, spherical more uniform field of a bar magnet. This actual subatomic quantum magnetic field of an electron at rest, is called Quantum Magnet or else a Magneton. It is today verified experimentally by quantum magnetic field imaging methods and sensors like SQUID scanning magnetic microscopy of ferromagnets and also seen in Bose-Einstein Condensates (BEC) quantum ferrofluids experiments. Normally, a macroscale bar magnet should behave like a relative giant Quantum Magnet with identical magnetic dipole field imprint since all of its individual magnetons collectively inside the material, dipole moments are uniformly aligned forming the total net field of the magnet. However due to Quantum Decoherence (QDE) phenomenon at the macroscale and macroscopic magnetic field imaging sensors limitations which cannot pickup these rapid quantum magnetization fluctuations, this field is masked and not visible at the macroscale. By using the relative inexpensive submicron resolution Ferrolens quantum magnetic optical superparamagnetic thin film sensor for field real time imaging and method we have researched in our previous publications, we can actually make this net magneton field visible on macroscale magnets. We call this net total field herein, Quantum Field of Magnet (QFM) differentiating it therefore from the field of the single subatomic magneton thus quantum magnet. Additionally, the unique potential of the Ferrolens device to display also the magnetic flux lines of this macroscopically projected giant Magneton gives us the opportunity for the first time to study the individual magnetic flux lines geometrical pattern that of a single subatomic magneton. We describe this particular magnetic flux of the magneton observed, quantum magnetic flux. Therefore an astonishing novel observation has been made that the Quantum Magnetic Field of the Magnet-Magneton (QFM) consists of a dipole vortex shaped magnetic flux geometrical pattern responsible for creating the classical macroscopic N-S field of magnetism as a tension field between the two polar quantum flux vortices North and South poles. A physical interpretation of this quantum decoherence mechanism observed is analyzed and presented and conclusions made showing physical evidence of the quantum origin irrotational and therefore conservative property of magnetism and also demonstrating that ultimately magnetism at the quantum level is an energy dipole vortex phenomenon.

Optimizing the formation of depth-confined nitrogen vacancy center spin ensembles in diamond for quantum sensing

Spin ensembles of nitrogen vacancy (NV) centers in diamond are emerging as powerful spin-based sensors for magnetic, electric and thermal field imaging with high spatial and temporal resolution. Here we characterize the formation of depth-confined NV center ensembles, activated by electron irradiation in diamond layers grown by plasma enhanced chemical vapor deposition with nitrogen co-doping. To do so, we exploit the high magnetic sensitivity of ensembles of NV centers to probe their spin environment as a function of growth and irradiation parameters. We engineer an NV ensemble whose magnetic sensitivity is within a factor of two of the static NV-NV dipolar interaction limit, thus demonstrating a powerful platform for quantum sensing.

(111)-oriented, single crystal diamond tips for nanoscale scanning probe imaging of out-of-plane magnetic fields

We present an implementation of all-diamond scanning probes for scanning nitrogen-vacancy (NV) magnetometry fabricated from (111)-oriented diamond material. The realized scanning probe tips on average contain single NV spins, a quarter of which have their spin quantization axis aligned parallel to the tip direction. Such tips enable single-axis vector magnetic field imaging with a nanoscale resolution, where the measurement axis is oriented normal to the scan plane. We discuss how these tips bring multiple practical advantages for NV magnetometry, in particular, regarding quantitative analysis of the resulting data. We further demonstrate the beneficial optical properties of NVs oriented along the tip direction, such as polarization-insensitive excitation, which simplifies optical setups needed for NV magnetometry. Our results will be impactful for scanning NV magnetometry in general and for applications in spintronics and the investigation of thin film magnets in particular.

Quantitative imaging of magnetic field distribution using a pyrene-based magnetosensing exciplex fluorophore.

Quantitative imaging of magnetic field distribution was carried out using a pyrene-based magnetosensing exciplex fluorophore, pyrene-(CH2)12-O-(CH2)2-N,N-dimethylaniline (Py-12-O-2-DMA), on a conventional fluorescence microscope with an off-the-shelf LED lamp. No continuous sample supply was required for the process. The solvent system (anisole : DMF, 50 : 50 (v/v)) was carefully selected for monitoring the extent of modulation caused by the external magnetic field. The emission from Py-12-O-2-DMA increased by ca. 1.5 times under an external magnetic field of 50 mT. The pyrene-based reporter was ca. 24.7 times brighter than a previously reported phenanthrene-based complex when excited by using the widely available 355 nm excitation. Moreover, the maximum wavelength up to which Py-12-O-2-DMA could be excited (up to 380 nm) was longer than the wavelength up to which Phen-12-O-2-DMA could be excited. The combined advantages allowed the capture of magnetic field images with a high S/N ratio under milder conditions such as low illumination power, reduced sample concentration, and simpler optical setup. The system was also found to be feasible for 3D magnetic field distribution imaging by two-photon fluorescence microscopy.

Formation of a Magnetic Flux Rope in the Early Emergence Phase of NOAA Active Region 12673

Abstract In this work, we investigate the formation of a magnetic flux rope (MFR) above the central polarity inversion line (PIL) of NOAA Active Region 12673 during its early emergence phase. Through analyzing the photospheric vector magnetic field, extreme ultraviolet (EUV) and ultraviolet (UV) images, extrapolated three-dimensional (3D) nonlinear force-free fields (NLFFFs), and the photospheric motions, we find that with the successive emergence of different bipoles in the central region, the conjugate polarities separate, resulting in collision between the nonconjugated opposite polarities. Nearly potential loops appear above the PIL at first, then get sheared and merge at the collision locations as evidenced by the appearance of a continuous EUV sigmoid on 2017 September 4, which also indicates the formation of an MFR. The 3D NLFFFs further reveal the gradual buildup of the MFR, accompanied by the appearance of two elongated bald patches (BPs) at the collision locations and a very-low-lying hyperbolic flux tube configuration between the BPs. Finally, the MFR has relatively steady axial flux and average twist number of around 2.1 × 1020 Mx and −1.5, respective. Shearing motions are found developing near the BPs when the collision occurs, with flux cancellation and UV brightenings being observed simultaneously, indicating the development of a process named collisional shearing (first identified by Chintzoglou et al.). The results clearly show that the MFR is formed by collisional shearing, i.e., through shearing and flux cancellation driven by the collision between nonconjugated opposite polarities during their emergence.

A critical review on the applications of fluid-structure interaction in porous media

PurposeThis study aims to investigate a critical review on the applications of fluid-structure interaction (FSI) in porous media.Design/methodology/approachTransport phenomena in porous media are of continuing interest by many researchers in the literature because of its significant applications in engineering and biomedical sectors. Such applications include thermal management of high heat flux electronic devices, heat exchangers, thermal insulation in buildings, oil recovery, transport in biological tissues and tissue engineering. FSI is becoming an important tool in the design process to fully understand the interaction between fluids and structures.FindingsThis study is structured in three sections: the first part summarizes some important studies on the applications of porous medium and FSI in various engineering and biomedical applications. The second part focuses on the applications of FSI in porous media as related to hyperthermia. The third part of this review is allocated to the applications of FSI of convection flow and heat transfer in engineering systems filled with porous medium.Research limitations/implicationsTo the best knowledge of the present authors, FSI analysis of turbulent flow in porous medium never been studied, and therefore, more attention should be given to this area in any future studies. Moreover, more studies should also be conducted on mixed convective flow and heat transfer in systems using porous medium and FSI.Practical implicationsThe wall of the blood vessel is considered as a flexible multilayer porous medium, and therefore, rigid wall analysis is not accurate, and therefore, FSI should be implemented for accurate predictions of flow and hemodynamic stresses.Social implicationsThe use of porous media theory in biomedical applications received a great attention by many investigators in the literature (Khanafer and Vafai, 2006a; Al-Amiri et al., 2014; Lasiello et al., 2016a, Lasiello et al., 2016b; Lasiello et al., 2015; Chung and Vafai, 2013; Mahjoob and Vafai, 2009; Yang and Vafai, 2008; Yang and Vafai, 2006; Ai and Vafai, 2006). A comprehensive review was conducted by Khanafer and Vafai (2006b) summarizing various studies associated with magnetic field imaging and drug delivery. The authors illustrated that the tortuosity and porosity had a profound effect on the diffusion process within the brain. AlAmiri et al. (2014) conducted a numerical study to investigate the effect of turbulent pulsatile flow and heating technique on the thermal distribution within the arterial wall. The results of that investigation illustrated that local heat flux variation along the bottom layer of the tumor was greater for the low-velocity condition. Yang and Vafai (2006) presented a comprehensive four-layer model to study low-density lipoprotein transport in the arterial wall coupled with a lumen (Figure 1). All the four layers (endothelium, intima, internal elastic lamina and media) were modeled as a homogenous porous medium.Originality/valueFuture studies on the applications of FSI in porous media are recommended in this review.

Principles and techniques of the quantum diamond microscope

AbstractWe provide an overview of the experimental techniques, measurement modalities, and diverse applications of the quantum diamond microscope (QDM). The QDM employs a dense layer of fluorescent nitrogen-vacancy (NV) color centers near the surface of a transparent diamond chip on which a sample of interest is placed. NV electronic spins are coherently probed with microwaves and optically initialized and read out to provide spatially resolved maps of local magnetic fields. NV fluorescence is measured simultaneously across the diamond surface, resulting in a wide-field, two-dimensional magnetic field image with adjustable spatial pixel size set by the parameters of the imaging system. NV measurement protocols are tailored for imaging of broadband and narrowband fields, from DC to GHz frequencies. Here we summarize the physical principles common to diverse implementations of the QDM and review example applications of the technology in geoscience, biology, and materials science.

Formation of perfectly aligned high-density NV centers in (111) CVD-grown diamonds for magnetic field imaging of magnetic particles

Magnetic field imaging of magnetic particles using diamond sensors with nitrogen-vacancy (NV) centers has the potential to become a new prominent living-cell observation method, because of the reduction of photodamage to cells. To realize a higher signal-to-noise ratio of magnetic detection, perfectly aligned and high-density NV centers in the diamond are required because they are effective in reducing optical shot noise. In this study, diamond films were grown by microwave plasma CVD on (111) substrates. The highest NV density with a perfectly aligned NV axis of 7 × 1017 cm−3 was obtained with a high growth rate due to the increase of vacancies, and the reduction of the optical shot noise to 1/4 was confirmed. Moreover, magnetic field imaging with different-thickness NVs in CVD-grown diamonds showed the dependence of the magnetic field distribution pattern and SNR on the diamond film thickness.

High-Density Large-Scale TMR Sensor Array for Magnetic Field Imaging

Magnetic field imaging (MFI) is widely used in electromagnetic nondestructive evaluation (ENDE). This paper presents a high-density, large-scale tunneling magnetoresistance (TMR) sensor array for MFI applied in ENDE. The TMR array consists of 180 sensing elements with the distance of 0.5 mm between any pair of TMR sensors adjacent to each other, which enables to acquire an image with high spatial resolution. With a total length of 90 mm, the TMR array is capable of imaging a rectangular area as wide as 90 mm in a single scan resulting in a fast inspection speed for the evaluation of structure with a large surface area. The proposed TMR sensor array has high sensitivity to the magnetic field in a wide frequency range. Therefore, it can be used for the detection of deeply embedded defects in multilayer riveted structures with excitation currents at ultralow frequencies. Experimental results show that machined notches under fasteners head at a distance of 8 mm from the top surface of a multilayer riveted aluminum structure can be detected with a proper fusion of the magnetic field images at 100 and 1000 Hz. Furthermore, surface notch with dimension $300\,\,\mu \text {m} \times 300\,\,\mu \text {m} \times 400\,\,\mu \text{m}$ on an aluminum sample can be detected from the obtained magnetic field image with excitation current frequency 20 kHz.

Zero-Field Magnetometry Based on Nitrogen-Vacancy Ensembles in Diamond

Ensembles of nitrogen-vacancy (NV) centers in diamonds are widely utilized for magnetometry, magnetic-field imaging and magnetic-resonance detection. They have not been used for magnetometry at zero ambient field because Zeeman sublevels lose first-order sensitivity to magnetic fields as they are mixed due to crystal strain or electric fields. In this work, we realize a zero-field (ZF) magnetometer using polarization-selective microwave excitation in a 12C-enriched HPHT crystal sample. We employ circularly polarized microwaves to address specific transitions in the optically detected magnetic resonance and perform magnetometry with a noise floor of 250 pT/Hz^(1/2). This technique opens the door to practical applications of NV sensors for ZF magnetic sensing, such as ZF nuclear magnetic resonance, and investigation of magnetic fields in biological systems.

Wideband microwave magnetometry using a nitrogen-vacancy center in diamond

Microwave magnetometry is essential to a variety of modern electronic techniques, most notably integrated circuits. The nitrogen-vacancy center in diamond has shown the ability of nanoscale resolution for the microwave magnetic field measurement and imaging. However, the characterization of the wideband magnetic field remains a challenge. Here we experimentally demonstrated a wideband microwave magnetometry with an off-resonance protocol based on the Bloch-Siegert shift effect. The off-resonance microwave magnetic field shifts the energy level of the nitrogen-vacancy center. It results in a phase accumulation during the evolution of the superposition state of the quantum sensor. According to this effect, by optimizing the evolution time, we experimentally verified the bandwidth widening of an order of magnitude compared with the Rabi oscillation, i.e., on-resonance method with an acceptable decrease of the sensitivity. In addition, we extracted the microwave frequency with a two-qubit system, which consists of a nitrogen-vacancy center and a nearby $^{13}\mathrm{C}$ nucleus. This approach enables the building of a wideband and potentially nanoscale microwave magnetometry to allow various potential applications, such as electronic circuits development.

High-Contrast Quantum Imaging with Time-Gated Fluorescence Detection

Optical detection of spin state has been widely used for the solid state spin qubit in the application of quantum information processing. The signal contrast determines the accuracy of quantum state manipulation, sensitivity of quantum sensing and resolution of quantum imaging. Here, we demonstrated a time-gated fluorescence detection method for enhancing the spin state signal contrast of nitrogen vacancy (NV) center in diamond. By adjusting the delay between time gate and the excitation laser pulse, we improved both the signal contrast and signal-to-noise ratio for NV spin detection. An enhancement ratio of 1.86 times was reached for the signal contrast. Utilizing the time-gated fluorescence detection, we further demonstrated a high contrast quantum imaging of nanoparticle's stray magnetic field. Without any additional manipulation of the quantum state, we expect that this method can be used to improve the performance of various applications with NV center.

Multifunctional graphene oxide/iron oxide nanoparticles for magnetic targeted drug delivery dual magnetic resonance/fluorescence imaging and cancer sensing.

Graphene Oxide (GO) has recently attracted substantial attention in biomedical field as an effective platform for biological sensing, tissue scaffolds and in vitro fluorescence imaging. However, the targeting modality and the capability of its in vivo detection have not been explored. To enhance the functionality of GO, we combine it with superparamagnetic iron oxide nanoparticles (Fe3O4 NPs) serving as a biocompatible magnetic drug delivery addends and magnetic resonance contrast agent for MRI. Synthesized GO-Fe3O4 conjugates have an average size of 260 nm and show low cytotoxicity comparable to that of GO. Fe3O4 nanoparticles provide superparamagnetic properties for magnetic targeted drug delivery allowing simple manipulation by the magnetic field and magnetic resonance imaging with high r2/r1 relaxivity ratios of ~10.7. GO-Fe3O4 retains pH-sensing capabilities of GO used in this work to detect cancer versus healthy environments in vitro and exhibits fluorescence in the visible for bioimaging. As a drug delivery platform GO-Fe3O4 shows successful fluorescence-tracked transport of hydrophobic doxorubicin non-covalently conjugated to GO with substantial loading and 2.5-fold improved efficacy. As a result, we propose GO-Fe3O4 nanoparticles as a novel multifunctional magnetic targeted platform for high efficacy drug delivery traced in vitro by GO fluorescence and in vivo via MRI capable of optical cancer detection.

Synthetic Magnetic Field Imaging With Triangle Excitation Coil for Inspection of Any Orientation Defect

Detection of any orientation defect that is deeply embedded under rivet head in multilayer riveted structure is a challenging task for eddy current testing (ECT). In this paper, a novel probe with right-angle triangle excitation coil and two tunneling magnetoresistance (TMR) sensor arrays is proposed to address this problem. The two TMR sensor arrays, which are capable of obtaining magnetic field images with spatial resolution of 0.5 mm, are placed on top of the two right-angle sides of the excitation coil measuring the normal component magnetic field. The probe moves along the direction of the long side of the triangular coil during the inspection. Therefore, the two sensor arrays scan the structure under test sequentially and two images are recorded. An image processing algorithm including data shifting, rotating, and multifrequency mixing is developed to fuse the two images, which results in a synthetic image. A prototype probe is built and tested to demonstrate the feasibility of the design. Three-layer aluminum samples with carbon steel rivet and defect located in the second and third layers are evaluated by the prototype probe. Defects with different sizes and orientations are imaged. Experiment results show that the proposed probe is capable of detecting defects in any direction. The signal processing algorithm highlights the defect information. The orientation angle of the defect can be estimated from the synthetic image.