Variable Magnetic Field Research Articles

Ferro-hydrodynamic induced convection flow and heat transfer of nanofluids in a corrugated wall enclosure

This study aims to improve heat transfer by utilizing Kelvin forces and inducing magnetic-induced convection in ferro-hydrodynamic convection, in conjunction with nanoparticle migrations. The fundamental equations governing the conservation of mass, momentum, energy, and nanoparticle mass were formulated as partial differential equations. As primary terms, the model incorporated the buoyancy, Lorenz, and Kelvin forces. In this context, temperature variations in the presence of a variable magnetic field generate a temperature-dependent body force. This can induce fluid circulation. Thus, even without gravitational force, magnetic force can stimulate convection heat transfer flows. The study thoroughly examined the impact of magnetic source placement on heat transfer. An increase in Ha from 0 to 100 reduced the average Nusselt number (NuAvg) by approximately 60% in all cases, regardless of the magnetic source position. However, the magnetic field number (Mnf) and its effect on NuAvg are dependent on the magnetic source's position.

Cryogenic spectroscopic imaging scanning tunnelling microscope in a water-cooled magnet down to 1.7 K

Spectroscopic-imaging scanning tunnelling microscope (SI-STM) in a water-cooled magnet (WM) at low temperature has long been desirable in the condensed matter physics area since it is crucial for addressing various scientific problems, such as the behaviour of Cooper electrons crossing Hc2 in a high-temperature superconductor. Here we report on the construction and performance of the first atomically resolved cryogenic SI-STM in a WM. It operates at low temperatures of down to 1.7 K and in magnetic fields of up to 22 T (the WM's upper safety limit). The WM-SI-STM unit features a high-stiffness sapphire-based frame with the lowest eigenfrequency being 16 kHz. A slender piezoelectric scan tube (PST) is coaxially embedded in and glued to the frame. A well-polished zirconia shaft is spring-clamped onto the gold-coated inner wall of the PST to serve both the stepper and the scanner. The microscope unit as a whole is elastically suspended in a tubular sample space inside a 1K-cryostat by a two-stage internal passive vibrational reduction system, achieving a base temperature below 2 K in a static exchange gas. We demonstrate the SI-STM by imaging TaS2 at 50 K and FeSe at 1.7 K. Detecting the well-defined superconducting gap of FeSe, an iron-based superconductor, at variable magnetic fields demonstrates the device's spectroscopic imaging capability. The maximum noise intensity at the typical frequency is 3 pA per square root Hz at 22 T, which is only slightly worse than at 0 T, indicating the insensitivity of the STM to harsh conditions. In addition, our work shows the potential of SI-STMs for use in a WM and hybrid magnet with a 50 mm-bore size where high fields can be generated.

In-Vehicle Phone Localization for Prevention of Distracted Driving

A new in-vehicle phone localization scheme, called DAPL (Detection and Alarming of in-vehicle Phone Location), is proposed to determine the locations of smartphones inside a moving car, with the goal of preventing smartphone-distracted driving. DAPL operates on commodity smartphones and cars, and does not require additional special/dedicated hardware to be installed inside the car, making its deployment easy and attractive to users and carmakers. Even when a phone is moved from one location to another inside a moving car, DAPL will detect this movement, acquire the sensor data, and estimate the phones destination location. DAPL captures the trajectory of each phone movement, the change of magnetic field, and the RSSI readings from the Bluetooth transceiver builtin most cars, and then estimates the phones destination location by matching the trajectory with the variation of magnetic field and the Bluetooth RSSI readings. Our extensive experimentation has shown DAPL to achieve an average of 91.71% accuracy of in-car phone localization at low energy overhead, i.e., <2.5% reduction of actual usage (screen-on) time.

Which Component of Solar Magnetic Field Drives the Evolution of Interplanetary Magnetic Field over the Solar Cycle?

The solar magnetic structure changes over the solar cycle. It has a dipole structure during solar minimum, where the open flux extends mainly from the polar regions into the interplanetary space. During maximum, a complex structure is formed with low-latitude active regions and weakened polar fields, resulting in spread open field regions. However, the components of the solar magnetic field that are responsible for long-term variations in the interplanetary magnetic field (IMF) are not clear, and the IMF strength estimated based on the solar magnetic field is known to be underestimated by a factor of 3–4 against the actual in situ observations (the open flux problem). To this end, we decomposed the coronal magnetic field into the components of the spherical harmonic function of degree and order (ℓ, m) using the potential field source surface model with synoptic maps from SDO/HMI for 2010–2021. As a result, we found that the IMF rapidly increased in 2014 December (7 months after the solar maximum), which coincided with the increase in the equatorial dipole, (ℓ, m) = (1, ±1), corresponding to the diffusion of active regions toward the poles and in the longitudinal direction. The IMF gradually decreased until 2019 December (solar minimum) and its variation corresponded to that of the nondipole component ℓ ≥ 2. Our results suggest that the understanding of the open flux problem may be improved by focusing on the equatorial dipole and the nondipole component and that the influence of the polar magnetic field is less significant.

Magnetotransport‐Induced Non‐Contact Terahertz Detection of Weak Magnetic Fields in Optically Thin Frequency‐Agile Superlattice Metasurfaces (Advanced Optical Materials 12/2023)

In article number 2202203, S. Karmakar, D. R. Chowdhury, and colleagues have demonstrated an optically thin superlattice metamaterial, which renders demarked ability to differentially tune its resonance frequencies with the combined effect of near-field coupling and spin-dependent magneto-transport mechanism at terahertz (THz) frequencies. Such resonance tuning characteristics (larger intensity modulation: dipole resonance, frequency modulation: Fano resonance) lead to accurate detection of minute variation of external magnetic fields (approximately few milli-tesla) with THz spectroscopy.

Magnetic Properties of Melt-Spun CoMnSi(B) Alloys

MnCoSi and MnCoSiB0.5 alloys were obtained by melt-spinning technique in order to attain polycrystalline microstructures with average grain sizes well below 10 microns. Phase distribution studied by X-ray analysis indicated single-phase materials with orthorhombic structure and TiNiSi-type crystal symmetry. Chemical homogeneity was verified by means of scanning electron microscopy, whereas magnetic behavior corresponded to soft magnetic materials with coercivity values lower than 20 Oe and saturation magnetization of 80 emu/g. Magnetocaloric response of these MnCoSiB alloys was characterized by a maximum magnetic entropy change of 1.0 J/kg K (for a magnetic field variation of 2.0 Tesla) and attractive refrigerant capacity over 100 J/kg, which represents a significant enhancement respect to equivalent MnCoGe alloys.

Magnetism and Exchange Bias Properties in Ba2ScRuO6

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba2ScRuO6 synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P3¯m1. The Rietveld refinement using the room-temperature powder XRD pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the DC electrical resistivity highlights a semiconducting behavior with the electron conduction corresponding to Mott’s 3D variable range hopping (VRH) model. The detailed magnetization measurements show that Ba2ScRuO6 develops antiferromagnetic ordering at TN≈ 9 K. Interestingly, below 9 K (TN), the field-cooled magnetic field variation (FC) of the magnetization curves highlights an exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to the inhomogeneous magnetic correlations due to the disorder in the structure. Remarkably, the appearance of a large exchange bias field in Ba2ScRuO6 indicates that inhomogeneous hexagonal double perovskites are a promising class to explore new materials having potential applications in spintronics.

Seismic Noise Reduction as a Function of Depth Recorded by a Vertical Array Installed in a 285-m-Deep Borehole at a Gas Storage Field in Northern Italy

Abstract The background seismic noise can be generated by different sources such as, ocean waves (microseisms), atmospheric disturbances (strong wind and storms), and anthropogenic activities, temperature changes and magnetic field variations. Such disturbances are characterized by specific frequency bands, time occurrence (diurnal and seasonal variation), and site location (close to populated areas or to the coasts). Reducing the pernicious effect of these noise sources is one of the main challenges that seismologists and engineers need to face when designing seismic monitoring networks and, more specifically when selecting the hosting site of a seismic station. A solution to partially attenuate the seismic noise effect is achieved by deploying seismic stations in boreholes. A general law estimating the sufficient depth to gain to detect even low seismic events, highly masked by background noise, is fundamental for defining the capability of microseismic network. Here, we aim to characterize the seismic noise level at S. Potito-Cotignola in the Po Valley, Italy, from January 2019 to December 2021 recorded by a broadband seismic station at surface and a vertical array composed by six short-period three-component seismometers installed at depth ranging between 35 and 285 m in borehole. We compute the amplitude noise reduction as a function of depth for different frequencies and we evaluate the depth dependency of the signal to noise ratio for 18 seismic events, with different magnitude (from −0.1 to 2.9) and hypocentral distances (from 12.9 to 37.2 km). Results show that (1) the dependence of noise level with depth follows a logarithmic empirical trend and (2) most of the selected seismic events show that signal to noise ratio increases with depth. The empirical relationships we estimated can be used to help the design of microseismic monitoring networks in similar geological settings.

Analysis of blood flow of unsteady Carreau-Yasuda nanofluid with viscous dissipation and chemical reaction under variable magnetic field

Blood flow analysis through arterial walls depicts unsteady non-Newtonian fluid flow behavior. Arterial walls are impacted by various chemical reactions and magnetohydrodynamic effects during treatment of malign and tumors, cancers, drug targeting and endoscopy. In this regard, current manuscript focuses on modeling and analysis of unsteady non-Newtonian Carreau-Yasuda fluid with chemical reaction, Brownian motion and thermophoresis under variable magnetic field. The main objective is to simulate the effect of different fluid parameters, especially variable magnetic field, chemical reaction and viscous dissipation on the blood flow to help medical practitioners in predicting the changes in blood to make diagnosis and treatment more efficient. Suitable similarity transformations are used for the conversion of partial differential equations into a coupled system of ordinary differential equations. Homotopy analysis method is used to solve the system and convergent results are drawn. Effect of different dimensionless parameters on the velocity, temperature and concentration profiles of blood flow are analyzed in shear thinning and thickening cases graphically. Analysis reveals that chemical reaction increases blood concentration which enhance the drug transportation. It is also observed that magnetic field elevates the blood flow in shear thinning and thickening scenarios. Furthermore, Brownian motion and thermophoresis increases temperature profile.

Thermal stability of 6-filament MgB2 wire with resistive CuNi sheath cooled by liquid He and water ice

In this paper, thermal stability of two 6-filament MgB2 wires with resistive CuNi sheath has been examined by DC transport measurements at the temperature of liquid He and variable external magnetic fields, and at variable temperatures of water ice under self-field conditions. Current-voltage characteristics up to the quench were performed and the operation limits of both wires under different cooling are analyzed and compared. The obtained results show that only 6 % of well conducting copper core allows to improve the thermal stability considerably, and it also limits the wire heating after the quench. MgB2 wires showed more stable operation after the quench under subcooled water ice in comparison to traditional Helium bath cooling, which offer a cheap and safe cooling mode for future devices.

Optimal classification and similarity solution for unsteady flow behind a shock wave in a perfectly conducting dusty gas with magnetic field using group invariance method

We have studied the one dimensional unsteady isothermal and adiabatic flows behind the shock waves in a non-ideal dusty gas under the effect of magnetic field using Lie group invariance method. This method is used to get the infinitesimal generators of the Lie algebra. The concept of optimal systems is used for minimizing the group-invariant solutions. The optimal system of subalgebra is used to obtain the similarity variables and similarity transformation which transform the set of partial differential equations (PDEs) into a set of ordinary differential equations (ODEs). Consequently, the system of ODEs in different cases is solved by using Runge–Kutta (R-K) method of forth order to derive the similarity solution in the cases of isothermal and adiabatic flows. The detailed discussions are illustrated by graph through numerical calculation in the case of power-law shock path. It is shown that the shock wave strength has decaying effects with an increase in the values of Alfven Mach number, adiabatic exponent of the gas, and gas non-idealness parameter. Also, the shock strength increases with an increment in the values of mass concentration of solid particles, magnetic field variation exponent, the ratio of density of solid particles to the gas initial density, and by changing the geometry from cylindrical to spherical.

A Revisit of Superconductivity in 4Hb-TaS2−2xSe2x Single Crystals

Previous investigations of 4$H_b$-TaS$_{2-2x}$Se$_{2x}$ mainly focused on the direct competition between superconductivity and charge density wave (CDW). However, the superconductivity itself, although has been prominently enhanced by isovalent Se substitution, has not been adequately investigated. Here, we performed a detailed electrical transport measurement down to 0.1 K on a series of 4$H_b$-TaS$_{2-2x}$Se$_{2x}$ single crystals. A systematic fitting of the temperature-dependent resistance demonstrates that the decreased Debye temperatures ($\Theta_{D}$) and higher electron-phonon coupling constants ($\lambda_{e-p}$) at the optimal Se doping content raise the superconducting transition temperature ($T_c$). Additionally, we discovered that the incorporation of Se diminishes the degree of anisotropy of the superconductivity in the highly layered structure. More prominently, a comprehensive analysis of the vortex liquid phase region reveals that the optimally doped sample deviates from the canonical 2D Tinkham prediction but favors a linear trend with the variation of the external magnetic field. These findings emphasize the importance of interlayer interaction in this segregated superconducting-Mott-insulating system.

Substantial enhancement in magnetic and magnetodielectric properties of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite

In pursuit of room-temperature magnetoelectric materials for numerous technological applications various materials are vigorously explored. Such is the motivation behind the synthesis of 0.7(Bi2Fe4O9)-0.3(La0.67Sr0.33MnO3) composite. The phase purity and structural analysis are examined through Rietveld refinement of room temperature X-ray diffraction (XRD) pattern, which shows that the composite has ‘Pbam + Pbnm’ phases. X-ray photoelectron spectroscopy confirmed the presence of mixed valence state of magnetic ions i.e. Fe2+ (41%), Fe3+ (45%), Fe4+ (14%) and Mn2+ (88%), Mn3+ (12%) favouring superexchange and double exchange interactions contributing to enhanced magnetizations. The presence of weak ferromagnetism in the composite is confirmed by large irreversibility in ZFC-FC data, isothermal magnetization curves and Arrott plots throughout the wide temperature range (10–300 K). High value of coercivity (Hc) is observed with an increase in temperature which indicates magnetic anisotropy in the system. Along with that, a plausible magnetodielectric (MD) coupling is evidenced in temperature dependent dielectric (ε′) and tan loss. Later, it is verified through intrinsic MD results carried out at higher frequency. At room temperature, the MD effect is found to be ∼2%. A contrasting behaviour in magnetic field variation of MD% is at 10 K and 300 K. However, a butterfly-shaped MD curve is evidenced where MD% ∼0.21% at 10 K. Lastly, Landau free energy expression confirmed that MD effect emerges from the coupling term ‘γP2M2′ where γ is ∼1.6 × 10−2 (emu/g)−2 and ∼1.1 × 10−2 (emu/g)−2 at 10 K and 300 K respectively. Thus, the above findings highlight the significance of the composite as a potential room temperature magnetoelectric material for device applications.

The role of the storm-time prompt penetrating electric field on the net distribution of plasma density over the low latitude ionospheric regions

The relative role of the prompt penetration of electric fields and neutral winds in the distribution of ionospheric plasma during geomagnetic storms over the Indian ionosphere region is studied in this paper. Four geomagnetic storms with similar onset times but of varying strengths have been analyzed with the help of data from ground-based magnetometers, and the ACE, GPS, and TIMED satellites. The strength and magnitude of the prompt penetration electric field were inferred from the magnetic field variations of the horizontal component of the magnetic field (ΔH) at Tirunelveli, a dip-equatorial station, using the ground-based magnetometers. The electron density distribution over the Indian ionospheric region was quantified using GPS-derived vertical total electron content (VTEC). Signatures of prompt penetration electric field were present for all the storms considered whose main phase was during the daytime. It is noted that as the strength of the penetration electric field increases, the latitudinal extent to which the electron density gets distributed also increases. The gradient in electron density extends even up to Shimla (a mid-latitude station) during a severe geomagnetic storm. The gradient was less for moderate geomagnetic storms. Since during the geomagnetic storm, a factor that controls electron density modulation is the neutral wind, its contribution is analyzed with the help of the thermospheric O/N2 ratio, measured by the global ultraviolet imager (GUVI) instrument, onboard NASA’s TIMED satellite. The observed increase in the O/N2 ratio does not correspond with the increase in the VTEC. We surmise that during the first day of the storm, the penetrating electric field is an essential factor that controls the electron density distribution in the low-latitude region. Later the plasma density distribution is controlled mainly by the thermospheric wind.

Numerical examination of wall properties for the magnetohydrodynamics stagnation point flow of micro-rotating fluid subject to weak concentration

In this investigation, stagnation point flow of non-Newtonian fluid is considered under the impact of magnetohydrodynamics, porous medium, and mixed convection effects. Additionally, angular momentum and energy transport constitutive equations are also taken into account in order to explore the fluid micro-rotational effects. The fluid motion develops by virtue of linear stretching and slip factors. Furthermore, the energy transport equation is raised with the effect of viscous dissipation and heat source phenomena. Mathematical formulations lead to a set of ordinary differential equations by introducing similarity variables. The proposed model has been solved numerically using fourth-order Runge–Kutta method with shooting technique. Influence of pertinent flow parameters for the case of weak concentration of micro-elements on velocity, temperature, skin friction, and local heat flux at the surface is computed and discussed. Different ranges are chosen for the flow parameters, for example; magnetic field variation is taken [0, 0.9], micro-rotation [0,1], stretching ratio [0,0.2], surface condition [0,1], the Prandtl number [3, 12], and the Eckert number [3, 11]. The fluid velocity slows down when the magnetic number varies from 0.0 to 0.5 in the presence of weak concentration (m = 0.5) of micro-elements. In addition, the maximum increasing percentage of skin friction is obtained when the porosity parameter varies from 0.0 to 0.6. The maximum decreasing percentage of the Nusselt number is obtained when the thermal slip parameter varies from 0.0 to 0.8. The current study has multiple fascinating applications in polymeric solutions, bio-medical functions like magnetic drug targeting, heat conduction in tissues, surface roughness, and squeeze film lubrication problems between conical bearings.

Study of Global Photospheric and Chromospheric Flows Using Local Correlation Tracking and Machine Learning Methods I: Methodology and Uncertainty Estimates

Cyclical variations of the solar magnetic fields, and hence the level of solar activity, are among the top interests of space weather research. Surface flows in global-scale, in particular differential rotation and meridional flows, play important roles in the solar dynamo that describes the origin and variation of solar magnetic fields. In principle, differential rotation is the fundamental cause of dipole field formation and emergence, and meridional flows are the surface component of a longitudinal circulation that brings decayed field from low latitudes to polar regions. Such flows are key inputs and constraints of observational and modeling studies of solar cycles. Here, we present two methods, local correlation tracking (LCT) and machine learning-based self-supervised optical flow methods, to measure differential rotation and meridional flows from full-disk magnetograms that probe the photosphere and text{H}alpha images that probe the chromosphere, respectively. LCT is robust in deriving photospheric flows using magnetograms. However, we found that it failed to trace flows using time-sequence text{H}alpha data because of the strong dynamics of traceable features. The optical flow methods handle text{H}alpha data better to measure the chromospheric flow fields. We found that the differential rotation from photospheric and chromospheric measurements shows a strong correlation with a maximum of 2.85~upmu text{rad},text{s}^{-1} at the equator and the accuracy holds until 60^{circ } for the MDI and text{H}alpha, 75^{circ } for the HMI dataset. On the other hand, the meridional flow deduced from the chromospheric measurement shows a similar trend as the concurrent photospheric measurement within 60^{circ } with a maximum of 20~text{m},text{s}^{-1} at 40^{circ } in latitude. Furthermore, the measurement uncertainties are discussed.

Study of the Relationship Between Sunspot Number and the Duration of the ≈ 1.6 – 2.2 Year Period in Neutron Monitor Counting Rates

Neutron monitor counting rates show periodicities in the ≈ 1.6 – 2.2-year range. These periodicities have been associated with a solar origin affecting the cosmic ray propagation conditions through the heliosphere. Our hypothesis is that the periodicities in the ≈ 1.6 – 2.2-years range correspond to a single periodicity that changes its duration over time.López-Comazzi and Blanco (Astrophys. J.927(2), 155, 2022) found that the duration of the ≈ 1.6 – 2.2-year period (tau ) is linearly related to the average sunspot number (SSN_{a}) in each solar cycle. The relationship shows that shorter ≈ 1.6 – 2.2-year periods occur during stronger cycles when SSN_{a} is higher. Therefore, the duration of this period varies from one solar cycle to another. This study focuses on this relation. For obtaining this relation, the values of the duration of the ≈ 1.6 – 2.2-year period in global neutron monitor counting rates (a virtual station determined by averaging of the different neutron monitor counting rates along the world) along the Solar Cycles 20 – 24 have been used. We extend the sample by adding the duration of the ≈ 1.6 – 2.2-year period in Huancayo neutron monitor counting rates along Solar Cycle 19 to this linear relationship. Once the linear relationship is extended, tau for the current Solar Cycle 25 is computed giving ≈ 2.24 years. Drawing on this more accurate relationship given by SSN_{a} = (-120 pm 10) : tau + (320 pm 20), we computed tau for the cycles previous to the existence of neutron monitors (Solar Cycles 7 – 18).These ≈ 1.6 – 2.2-year periodicities in neutron monitor counting rates could be produce by variations in the solar magnetic field due to an internal mechanism of the solar dynamo called Rossby waves. Concretely, the harmonic of fast Rossby waves with m=1 and n=8 fit with the detected ≈ 1.6 – 2.2-year periodicity. In addition, the variation of the solar magnetic-field strength from weaker to stronger solar cycles could explain the different periods detected in each cycle. Based on the detected periodicities using the dispersion relation for fast Rossby waves, a solar tachocline magnetic-field strength of ≈ 7 – 25 kG has been estimated.

Theoretical analysis of low frequency dust cyclotron waves with dust charge variations

The propagation of nonlinear dust cyclotron (DC) cnoidal waves having superthermal distributed electrons and ions in the presence of external magnetic field and adiabatic dust charge variation is investigated. The effect of dust charge variation is profoundly modified due to the presence of the superthermal electrons and ions. The dust charge variation parameter decreases with an increase in the superthermality index of ions. Adopting the reductive perturbation approach, it is shown that the dynamics of the cnoidal structure is modeled by a Korteweg–de Vries equation. It is found that only negative potential DC cnoidal and solitary structures are observed in such a plasma. The results further reveal that the cnoidal structures strongly depend on the degree of superthermality, dust charge variation parameter, temperature and number density of fluid particles, angle of obliqueness, as well as on the magnetic field strength. The numerical results confirm that as the dust charge variation enters the picture, amplitude as well as the width of the cnoidal waves enhances. Furthermore, the analysis is performed through Sagdeev potential, plane phase plot and spatial variation of potential to elucidate various aspects of the cnoidal wave dynamics in the presence of the adiabatic dust charge variation.

Variable magnetic field electron spectrometer to measure hot electrons in the range of 50-460 keV.

Resonance absorption (RA) occurs when a p-polarized electromagnetic wave, obliquely incident on an inhomogeneous plasma, tunnels past its turning point and resonantly excites an electron plasma wave (EPW) at the critical density. This phenomenon is important, for instance, in the direct drive approach to inertial fusion energy and is a particular example of a wider phenomenon in plasma physics known as mode conversion, which is crucial for heating magnetic fusion devices, such as tokamaks, via RF heating. Direct measurement of these RA-generated EPW accelerated hot electrons, with energy in the range of a few tens to a few hundreds of keV, is a challenging task due to the relatively low deflecting magnetic fields needed. The solution described here is a magnetic electron spectrometer (MES) with a continually changing magnetic field, lower at the entrance of the MES and gradually increasing toward the end, that enables the measurement of a wide spectral range of electrons with energies between 50 and 460keV. Electron spectra taken in a LaserNetUS RA experiment were acquired from plasmas generated by irradiating polymer targets with the combination of an ∼300ps pulse followed by a series of ten high intensity 50-200fs duration laser pulses from the ALEPH laser at Colorado State University. The high intensity beam is designed as spike trains of uneven duration and delay pulses in order to modify the RA phenomenon.

Online measurement of tetraethyllead in aqueous samples utilizing monolith-based magnetism-enhanced in-tube solid phase microextraction coupled with chromatographic analysis

A new procedure that utilizing a preconcentration system based on magnetism-enhanced in-tube solid phase microextraction (ME/IT-SPME) and detection by HPLC with diode array detector (DAD) after liquid desorption from the microextraction column has been developed for the online measurement of tetraethyllead (TEL) in various aqueous samples. In this connection, according to the chemical features of TEL, porous monolith mingled with Fe3O4 nanoparticles were designed and synthesized in a silica capillary, and used as the microextraction column of ME/IT-SPME. To favor the implement of variable magnetic fields during extraction procedure, the as-prepared microextraction column was twined a magnetic coil. Results revealed that the exertion of magnetic field during the adsorption and eluting procedures assisted the extraction of TEL with an enhancement by 52% in extraction efficiency. Under the most beneficial conditions, the developed ME/IT-SPME was online hyphenated with HPLC/DAD to measure trace TEL in various aqueous samples. The limit of detection was 0.082 μg/L and the RSDs for precision were in the range of 6.3–8.5%. The recoveries with low, medium and high fortified levels varied from 80.6% to 95.0% with good repeatability. To the best of knowledge, this is the first study that using IT-SPME to extract TEL and then online quantification with HPLC/DAD.