Search

This paper presents an experimental approach to maximizing the voltage generated by NaxCoO2 and improving the overall efficiency of the p-type thermoelectric leg by doping with Na up to x = 0.88. Two samples with different geometries were tested, each measured with and without an additional magnetic field applied in the direction of the temperature gradient. The properties of sodium cobaltite in response to hydration were explored, at temperatures between 300   a n d   380 K. Water injection boosted the current and power up to 75–100 µW at a temperature of 350–360 K. This power boost can be attributed to an electron-ion fluid flow pattern maintained by the longitudinal thermomagnetic effect and by water molecules forming hydrogen bonds with oxygen atoms in the CoO2 layers, inside the material. An electronic circuit was designed to boost the voltage to the desired level, for three or more sodium cobaltite samples mounted in parallel, and to store the energy in a supercapacitor. The output voltage and resistivity change of sodium cobaltite samples can be readily used as a humidity and temperature-sensing element in a transducer when paired with an appropriate electronic conditioning scheme. [ABSTRACT FROM AUTHOR]

An off-stoichiometric Fe 2 MnSn alloy was prepared by vacuum arc melting and homogenized by vacuum annealing. The structural analysis indicated that the alloy exhibits a D0 19 hexagonal structure. Isothermal magnetization analysis at room temperature showed soft ferromagnetic behavior and exchange magnetic anisotropy. Furthermore, the isofield magnetization study revealed a Curie temperature ( T c ) of 455 K with a second-order magnetic phase transition. A similar trace of the transition point was observed in the differential scanning calorimetric analysis. We estimated a magnetic entropy change ( Δ S M = − 4 J kg - 1 K - 1 ) and refrigerant capacity (RC = 116 J kg - 1 ) from M-T measurements, highlighting its potential for thermomagnetic generators and magnetic refrigerator applications. [ABSTRACT FROM AUTHOR]

The influence of sample geometry on various measured physical properties (including the magneto-Seebeck effect, Nernst effect, magnetoresistance effect, Hall effect, and thermal conductivity) in the presence of a magnetic field was examined using a polycrystalline Bi-Sb sample. The sample, consisting of polycrystalline Bi88Sb12, was prepared through spark plasma sintering and subsequent annealing. Measurements of the physical properties were conducted under a magnetic field of 5 T, and the obtained values were compared with simulated results derived using the finite element method for different sample geometries. Distinct shapes were found to be necessary for accurate measurements, with each physical property requiring a specific aspect ratio of sample length (l) to width (w). These ratios were determined to be l/w > 0.57, 2.9, 4.2, 1.2, and 3.1 for the magnetoresistance, Hall, two-wire magneto-Seebeck, four-wire magneto-Seebeck, and Nernst effects, respectively. Additionally, to achieve a minimal error of less than 2% in thermal conductivity measurement, a thermal conductance ratio of Ks/Kw > 27 was necessary, where Ks and Kw denote the thermal conductance of the sample and lead wire, respectively. [ABSTRACT FROM AUTHOR]

Presented work concerns thermally activated 2D materials inducing an electric field in the presence of a magnetic field. The thermomagnetic Nernst effect combines these quantities, and several works reveal results that could be used for validation of the experimental setup before investigations of other structures with potential thermomagnetic effects. The paper shows experimental studies on the thermomagnetic Nernst effect observed in pure nickel samples. The scope of experimental studies covers relationships of the sensitivity of the Nernst coefficient to magnetic field ranging to 1 T and temperature gradient above room temperature. The obtained results were discussed in relation to the referenced works. [ABSTRACT FROM AUTHOR]

Thermomagnetoelectric effect for the dielectric hydrodynamic system is considered. It is established that in a liquid, which is placed in a magnetic field, the temperature gradient can cause a convective mass flow, which leads to the appearance of an electric field in the surrounding space. The distribution of electric potential for various geometric implementations is calculated. A comparison of the obtained effect for normal and superfluid 4He is performed. [ABSTRACT FROM AUTHOR]

Purpose: The adverse effects of temperature on the lubricating properties of nano magnetorheological grease are reduced by applying of a magnetic field. Design/methodology/approach: Nano magnetorheological grease was prepared via a thermal water bath with stirring. The lubricating properties of the grease were investigated at different temperatures. Then the lubricity of the prepared nano magnetorheological grease was investigated under the effect of thermomagnetic coupling. Findings: As the temperature rises, the coefficient of friction of grease lubrication gradually increases, surface wear gradually increases and lubrication performance gradually decreases. Compared with grease, magnetorheological grease has a decreased coefficient of friction and enhanced lubrication effect under the action of a magnetic field at different temperatures. Originality/value: A lubrication method using a magnetic field to reduce the effect of temperature is established, thereby providing new ideas for lubrication design under a wide range of temperature conditions. [ABSTRACT FROM AUTHOR]

In this review, we consider the impact of magnetic field on the properties of strongly correlated heavy-fermion compounds such as heavy-fermion metals and frustrated insulators with quantum spin liquid. Magnetic field B can be considered a universal tool, allowing the exploration of the physics controlling the remarkable properties of heavy-fermion compounds. These vivid properties are T / B scaling, exhibited under the application of magnetic field B and at fixed temperature T, and the emergence of Landau Fermi liquid behavior under the application of magnetic field. We analyze the influence of quasiparticle–hole asymmetry on the properties of heavy-fermion (HF) compounds such as the universal scaling behavior of the thermopower S / T exhibited under the application of magnetic field B. We show that universal scaling is demonstrated by different HF compounds such as β - YbAlB 4 , YbRh 2 Si 2 , and strongly correlated layered cobalt oxide [ BiBa 0.66 K 0.36 O 2 ] CoO 2 . Analyzing YbRh 2 Si 2 , we show that the T / B scaling behavior of S / T is violated at the antiferromagnetic phase (AF) transition. The residual resistivity ρ 0 and the density of states N 0 experience jumps at the AF transition, causing two jumps in the thermopower and its sign reversal. Our consideration is based on the flattening of the single-particle spectrum that strongly affects ρ 0 and N 0 and leads to the violation of particle–hole symmetry. The particle–hole asymmetry generates the asymmetrical part Δ σ d (V) of tunneling differential conductivity σ d (V) , Δ σ d (V) = σ d (V) − σ d (− V) , where V is the voltage bias. We demonstrate that in the presence of magnetic field, the quasiparticle–hole asymmetry vanishes, the LFL behavior is restored, and the asymmetry disappears. Our calculations of the mentioned properties of HF compounds, based on the fermion condensation theory, are in good agreement with the experiment and support our conclusion that the fermion condensation theory is capable of describing the properties of HF compounds, including those exhibited under the application of magnetic field. [ABSTRACT FROM AUTHOR]

Using the method of SQUID magnetometry, the features of the antiferromagnet-ferromagnet thermomagnetic transition in arrays of the nanosized disks of Py/NiCu/Py synthetic antiferromagnets (SAFs) have been investigated. The effective interlayer interaction in individual SAFs "ferromagnet/diluted ferromagnet/ferromagnet" (F2/f/F1) changes from high-temperature antiferromagnetic to low-temperature ferromagnetic upon the transition at the Curie temperature T C f of the interlayer f. Temperature dependence of the magnetic parameters of individual layers and their effect on the features of the thermomagnetic transition are determined. The observed properties are important for the development of temperature-controlled nanoscale SAFs and multilayer nanostructures based on them. [ABSTRACT FROM AUTHOR]

Low-grade thermal energy, either from waste heat or from natural resources, constitutes an enormous energy reserve that remains to be fully harvested. Harvesting low-grade heat is challenging because of the low Carnot efficiency. Among various thermal energy harvesting mechanisms available for capturing low-grade heat (temperature less than 100 °C), the thermomagnetic effect has been found to be quite promising. In this study, we demonstrate a scalable thermomagnetic energy harvester architecture that exhibits 140% higher power density compared to the previously published spring–mass designs. The alternating force required to oscillate the thermomagnetic mass is generated through the interaction between two magnetic forces in opposite directions. We employed numerical modeling to illustrate the behavior of a thermomagnetic device under different operating conditions and to obtain the optimal hot-side and cold-side temperatures for continuous mode operations. A miniaturized thermomagnetic harvester was fabricated and experiments were conducted to systematically evaluate the performance. The prototype was found to exhibit an oscillation frequency of 0.33 Hz, a work output of 0.6 J/kg/cycle, and a power density of 0.2 W/kg of gadolinium under the temperature difference of 60 K. [ABSTRACT FROM AUTHOR]

We report the anomalous Nernst effect (ANE) in bulk La1-xNaxMnO3 (x = 0.02, 0.05, 0.1, and 0.3) samples whose ferromagnetic Curie temperature (TC) is tunable from 251 K to 310 K. The ANE voltage abruptly increases at TC and decreases for T < TC. The maximum value of ANE is achieved for x = 0.1, which shows the highest magnetization value in the series. The temperature dependent ANE (T < TC) is analyzed with the help of dc resistivity and longitudinal thermopower data using Mott's relation, and it is found that the ANE in La1-xNaxMnO3 is dominated by skew scattering. [ABSTRACT FROM AUTHOR]

We report the anomalous Nernst effect (ANE) in bulk La1-xNaxMnO3 (x = 0.02, 0.05, 0.1, and 0.3) samples whose ferromagnetic Curie temperature (TC) is tunable from 251 K to 310 K. The ANE voltage abruptly increases at TC and decreases for T < TC. The maximum value of ANE is achieved for x = 0.1, which shows the highest magnetization value in the series. The temperature dependent ANE (T < TC) is analyzed with the help of dc resistivity and longitudinal thermopower data using Mott's relation, and it is found that the ANE in La1-xNaxMnO3 is dominated by skew scattering. [ABSTRACT FROM AUTHOR]

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb. [ABSTRACT FROM AUTHOR]

In our recent studies, we have developed a thermodynamic biochemical model able to select the resonant frequency of an extremely low frequency electromagnetic field (ELF-EMF) specifically affecting different types of cancer, and we have demonstrated its effects in vitro. In this work, we investigate the cellular response to the ELF electromagnetic wave in three-dimensional (3D) culture models, which mimic the features of tumors in vivo. Cell membrane was modelled as a resistor–capacitor circuit and the specific thermal resonant frequency was calculated and tested on two-dimensional (2D) and three-dimensional (3D) cell cultures of human pancreatic cancer, glioblastoma and breast cancer. Cell proliferation and the transcription of respiratory chain and adenosine triphosphate synthase subunits, as well as uncoupling proteins, were assessed. For the first time, we demonstrate that an ELF-EMF hampers growth and potentiates both the coupled and uncoupled respiration of all analyzed models. Interestingly, the metabolic shift was evident even in the 3D aggregates, making this approach particularly valuable and promising for future application in vivo, in aggressive cancer tissues characterized by resistance to treatments. [ABSTRACT FROM AUTHOR]

Developing new energy generation technologies able to effectively convert low‐grade thermal energy into electricity is an urgent necessity to tackle the continuous surge in energy demand and mitigate climate change. Here, a hybrid device that couples triboelectric and thermomagnetic effects to generate electrical power in the presence of small temperature gradients near room temperature is demonstrated. The thermomagnetic effect allows to induce the periodic and sustained motion of a second‐order ferromagnetic material in temperature gradients below 30 °C. This mechanical motion is then converted into electrical energy using a low‐cost triboelectric nanogenerator (TENG). The applicability of this concept is demonstrated in a broad range of operating temperatures in both the cold (15 to 37 °C) and hot (60 to 90 °C) sides. It is further shown that the electrical power generated by the hybrid TENG is more than 35× higher than that obtained by a conventional thermomagnetic generator driven by magnetic induction. The obtained results show that this implementation is a feasible thermal energy conversion technology, further expanding the applicability of triboelectricity into the realm of room temperature thermal harvesting. [ABSTRACT FROM AUTHOR]

Recently, the low frequency thermomagnetic effects on cancer cells have been analysed, both theoretically and experimentally. They have been explained by introducing an equilibrium thermodynamic approach. But, in this context, two related open problems have been highlighted: (1) Does there exist a magnetic interaction or do there exist any other processes? (2) Do there exist also thermal effects? Here, we introduce a non-equilibrium thermodynamic approach in order to address an answer to these questions. The results obtained point out that: (a) the effect produced by the electromagnetic wave is just a consequence of the interaction of the magnetic component of the electromagnetic wave with the biological matter; (b) the interaction of the electromagnetic wave causes also thermal effects, but related to heat transfer, even if there have been applied low frequency electromagnetic waves; (c) the presence of the magnetic field generates a symmetry breaking in the Onsager's coefficients, with a related perturbation of the cancer stationary state. [ABSTRACT FROM AUTHOR]

The prospect of altering the thermophysical properties of ferrofluid with an influence of magnetic field leads to improving natural convection in various heat transfer systems. This investigation principally focuses on the studies of electromagnetism-based turbulent natural convection heat transfer of low-density disk-shaped magnesium ferrite/water-based ferrofluid, filled in a novel heat pipe-assisted cubical cavity at various volume fractions. Two flat plate heat pipes were used to maintain temperature differences in the cavity. To advance the buoyancy of the working fluid inside the cavity, deliberately low-density ferrofluid containing disk-shaped particles was formulated using the hydrothermal method. The temperature difference between the two heat pipe-assisted vertical walls was sustained with four distinct temperature ranges from 10 to 25 °C. The ferrofluid filled in the cavity was then subjected to magnetic field ranging from 0 to 350 G to understand the thermomagnetic convection effects on heat transfer. The optimal volume fraction of ferrofluid for maximum heat transfer was found to be 0.05% at a wall temperature difference of 25 °C, owing to 23.51% improvement in average heat transfer coefficient along with 33.37% improvement in average Nusselt number when compared to water. With the application of a magnetic field of 350 G, the average heat transfer coefficient was further enhanced by 10.11%, and the average Nusselt number improved by 6.28% for 0.05% volume fraction in comparison to the condition where no magnetic field was applied. [ABSTRACT FROM AUTHOR]

A method to compare the thermal to magnetic transduction efficiencies of different thermomagnetic systems was developed. The efficiencies of operating about a spin reorientation transition and the alternative ferromagnetic to paramagnetic transformation at the Curie point were directly compared. A case study was performed comparing Gd operating about its spin reorientation temperature and its Curie point. Additionally, a case study on NdCo5 operating about its spin reorientation temperature using experimentally derived values of the materials' temperature dependent magnetic properties was conducted. Analysis suggests that choosing the appropriate material and operating it about its transition produces considerable efficiencies (∼22%) as well as large harvestable energy densities (∼2.6MJ/m³), which is an order of magnitude larger than Gd single domains operating about their Curie point (∼100 kJ/m³). [ABSTRACT FROM AUTHOR]

Magneto-optical imaging films (MOIFs) were used for the study of magnetic stray field distributions above topographically and thermomagnetically patterned permanent magnet films and other miniature elements that could be used in magnetic micro-systems. Calibrated external bias fields were applied to the samples in situ to simplify the graduation procedure, to expand the measurement range and to minimize the measurement errors. Both uniaxial and planar MOIF were used to make quantitative measurements. A scheme for the fast reconstruction of magnetic serial sections of nonuniform field profiles is proposed. The usefulness of biased MOIF imaging is illustrated by a number of specific examples, such as mechanical hole-drilling adapted to the case of magnetic analysis, dynamic range expansion beyond the limits set by MOIF saturation, rendering surface magnetic flux variations at the microscale and in the presence of strong background. [ABSTRACT FROM AUTHOR]

In magnetism literature, usually the applied or external field H0 is taken to present the results of an investigation. But for certain purposes, it is advantageous to work with the internal magnetic field H that occurs inside a magnetic body. It is well-known that the susceptibility of the material and the demagnetization effect, given by the geometry of a body, link the two usually different fields under consideration. If a probe is a long needle with the external magnetic field and the magnetization in the probe parallel to the axis of the slender body, the two fields are identical. But when building thermomagnetic machines, other demands may require also other shapes (porous materials, particle beds, wavy structures, etc.) of the magnetized material and then a correct distinction of these fields becomes important and in some cases also laborious if one of them must be theoretically determined from the other. This article shows how--from a theoretical point of view--the most important physical properties of thermomagnetism/magnetocalorics, namely, the adiabatic entropy change, the effective specific heat capacity, and the adiabatic temperature change must be transformed. Furthermore, this theory reveals the invariants of magnetocalorics, which are combinations of these three most important properties. [ABSTRACT FROM AUTHOR]

The impact of B substitution in Ni50Mn35In15-xBx Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5-400 K). Direct adiabatic temperature change (DTAD) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H=0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔTAD=2.5K was observed at the magnetostructural transition for Ni50Mn35In14.5B0.5. [ABSTRACT FROM AUTHOR]

Ferromagnetic Fe-Ni-Co-Al-(Ta,Nb)-B microwires with diameters from 170 lm to 50lm, which possess both superelastic and good magnetic properties, have been prepared by rapid quenching from the melt using the in rotating water spinning technique followed by cold-drawing and ageing. The cold-drawing and annealing processes lead to the initialization of premartensitic phases as confirmed by the X-ray diffraction and scanning transmission electron microscopic investigations, more significantly in the 50 μm cold-drawn microwires. An increase in the coercive field and in the saturation magnetization has been obtained by annealing, more importantly in the case of Nb-containing alloy. Ageing by thermal or current annealing led to the initialization of the superelastic effect. High values of strain of up to 1.8%, very good repeatability under successive loading, and values of superelastic effect of up to 1.2% have been achieved. The structural analysis coupled with the stress-strain data suggests that these materials annealed at 800 °C have superelastic potential at reduced ageing times. The magnetic behavior was found to be easily tailored through both thermal and thermomagnetic treatments with changes in the magnetic parameters which can be contactless detected. The results are important for future applications where both mechanical and magnetic properties matter, i.e., sensing/actuating systems. [ABSTRACT FROM AUTHOR]

Measurements of the adiabatic temperature change (ΔT) and the specific heat transfer (ΔQ) of Ni2.18Mn0.82Ga Heusler alloy were taken in order to quantify the direct giant magnetocaloric effect of the alloy when it is in the vicinity of magneto-structural phase transition (PT) from paramagnetic austenite to ferromagnetic martensite, and their results are presented. A new vacuum calorimeter was used to simultaneously measure ΔT and ΔQ of magnetocaloric materials with a Bitter coil magnet in fields of up to H=140 kOe. Other thermomagnetic properties of this alloy were investigated using standard differential scanning calorimetry and PPMS equipment. The maximal values of magnetocaloric effect in H=140 kOe were found to be ΔT=8.4K at initial temperature 340K and ΔQ=4900 J/kg at 343 K. Using this direct method, we show that the alloy indeed demonstrates the largest value of ΔQ as compared with previously published results for direct measurements of magnetocaloric materials, even though at 140 kOe the magnetic field-induced magnetostructural PT is still not complete. [ABSTRACT FROM AUTHOR]

Energy consumption levels show a never‐ending increase since the industrial era. Toward sustainability objectives, it is of outstanding importance to reduce the amount of wasted energy, that typically comes as waste heat, as a consequence of nonunitary efficiency of any thermodynamic process. Herein, a breakthrough in conversion of low enthalpy heat into electricity is presented, based on a liquid state device that operates through multiphysics effects: thermomagnetic advection, triboelectricity, pyroelectricity, and Ludwig–Sorét effect. A synergistic interaction between ferroelectric surfaces and a complex composition colloidal suspension is evidenced, owing to an enhancement of the generated potential of 365% in comparison with pyroelectric effect and 267% in comparison with triboelectric effect, while the current extracted is 54% higher than the pyroelectric effect only and the power extracted by induction remains substantially unperturbed. The impact of this technology on society is also analyzed, on the basis of a set of practical applications, by means of a computational analysis. [ABSTRACT FROM AUTHOR]

We use a three-flavor Nambu–Jona-Lasinio model to study the thermodynamics of strange quark matter under a strong magnetic field. The model Lagrangian features flavor SU(3) four-quark interactions and six-quark interactions that break the U A (1) symmetry. We incorporate thermomagnetic effects in the four-quark coupling by fitting lattice results for the average of u and d quark condensates close to the pseudocritical temperature. We compute the pressure at the mean field level and obtain the magnetization of quark matter. We adopt the recently proposed vacuum magnetic regularization (VMR) scheme, in that divergent quark mass independent contributions are not subtracted, thereby avoiding unphysical results for the magnetization. We devote special attention to the renormalized magnetization, a projected quantity that allows for direct comparisons with lattice QCD simulations. Our results are in very good agreement with lattice data indicating a paramagnetic behavior for quark matter. [ABSTRACT FROM AUTHOR]

A nonlinear study is made to find the influence of transverse anisotropy on the onset of thermomagnetic convection in a homogeneous and rotating porous medium. The medium is filled with a magnetic fluid and is subjected to centrifugal force with alternating directions. Unconditional nonlinear stability bounds are found by exploiting the variational principles. Effects of various parameters on the stability threshold are discussed. The overpredicting nature of the linear theory is demonstrated by isolating the subcritical region which cannot be obtained a priori. [ABSTRACT FROM AUTHOR]

The surface current density of charge carriers in two-dimensional doubly periodic n-type semiconductor superlattices in an external magnetic field in the presence of temperature gradient has been calculated in the single-electron approximation. The magnetic field was assumed to be permanent, homogeneous, and oriented perpendicular to the electron-gas plane. A joint solution of the Schrödinger equation and kinetic Boltzmann equation showed that the dependences of the surface density of transverse current on temperature and temperature-gradient magnitude are significantly nonlinear and contain portions with negative transverse differential conductivity. The dependence of the relaxation time on the electron quasi-momentum is phenomenologically taken into account in the model via the dispersion relation for carriers in magnetic subbands. [ABSTRACT FROM AUTHOR]

The benefit of transformer oil seeded with magnetic nanoparticles (forming a transformer oil-based ferrofluid) is numerically studied in an axisymmetric model of 40 kVA transformer. The maximum temperature in the system is decreased by 2.2 °C when using ferrofluid instead of transformer oil. This effect is mainly due to the magnetic body force, which modifies the convective flow in the system and enhances heat transfer. The leakage magnetic field is highly localized and limits the effect of thermomagnetic convection. Varying the geometry of the primary coil assembly allows to increase this effect and to decrease the maximum temperature. [ABSTRACT FROM AUTHOR]

Most spin caloritronics research utilizes thin films on substrates with an in-plane heat flow, where an unintended out-of-plane thermal gradient may develop by heat dissipation through the substrate. In systems exploiting metallic ferromagnets to generate or detect spin currents, such out-of-plane thermal gradients might confuse the signal via undesirable thermomagnetic effects, such as the anomalous Nernst effect. Here, we report direct measurement of the spin current created by the spin Nernst effect in platinum, using ferromagnetic metal contacts as spin accumulation detectors. By comparing the voltage measured transverse and longitudinal to the thermal gradient, we find that the device geometry is crucial in all-metallic systems. Exploiting the orthogonality in the angular dependence on the external magnetic field of the transversely measured voltage, we quantitatively separate the spin Nernst signal from the parasitic anomalous Nernst voltage, which are of the same order of magnitude. As a result, we estimate the spin Nernst angle of platinum to be comparable to the spin Hall angle in magnitude with an opposite sign. [ABSTRACT FROM AUTHOR]

Some of the advances made in the literature to understand the phase transitions of quark matter in the presence of strong magnetic field and finite temperature (zero quark chemical potential) are reviewed. We start by discussing the physics behind the Magnetic catalysis (MC) at zero/finite temperature and then focus on the lattice predictions for inverse magnetic catalysis (IMC) at high temperature and strong magnetic fields. Possible explanations for the IMC are covered, as well. Finally, we discuss recent efforts to modify QCD (quantum chromodynamics) effective models to reproduce the IMC observed on the lattice simulations. We emphasize the fact that applying thermomagnetic effects on the coupling constant of the NJL model significantly improve the effectiveness of the NJL model to obtain a reasonable physical description of hot and magnetized quark matter being in agreement with lattice results. [ABSTRACT FROM AUTHOR]

Thermomagnetic properties and geothermal energy potential in parts of Bida Basin, Nigeria have been evaluated using spectral analysis of integrated nine aeromagnetic data. The study area covering 27.225 km2 of aeromagnetic data was examined and construed in order to delineate the thermal properties of the country-rock in the area. The result of the visual inception of the residual map reveals that the area comprises an extremely irregular pattern of magnetic intensities that range from 220 to 240 nT. Two structural features of folding evidence were also delineated in the area namely; uplift and depression. The result of the lineament structures from the shaded relief map and Rose diagram depicts NE-SW as the major trend with the minor trend is NW - SE. Two depths to magnetic sources were distinguished in the area: the shallower bodies which vary from 1.27 to 1.96 km and the deeper bodies that vary from 2.01 to 4.27 km. The result also shows an average depth to the centroid as 12.97 km in the area. The thermomagnetic properties analysis show average values of 23.12 km Curie isotherm, 25.27 °C/km geothermal gradients and 63.17 mWm2²heat fow in the area. The study concludes that the study area possesses good potential quality for geothermal energy generation and exploration. [ABSTRACT FROM AUTHOR]

Magnetic properties of compacted Sm0.1Ca0.9MnO3 particles with 25 and 60 nm average sizes have been investigated. Particular attention has been paid to Griffiths-like features at temperatures above magnetic transition temperature TC and to the system glassiness at low temperatures. Griffiths-like features in inverse magnetic susceptibility of Sm0.1Ca0.9MnO3 nanoparticles have been linked to the presence of short range ferromagnetically correlated spin clusters above TC. Glassy behavior has been revealed in temperature and frequency dependence of ac-susceptibility, temperature and field dependence of thermoremanent and isothermoremanent magnetization, and time decay of the remanent magnetization. Experiments revealed the major impact of the glassy component on magnetic properties of investigated nanoparticles. The magnetic relaxation associated with glassy features was found to be much more pronounced in smaller particles, where a formation of collective state in an ensemble of phase separated nanoparticles may take place. Thermomagnetic irreversibility found in Sm0.1Ca0.9MnO3 nanoparticles has been linked to martensitic strain effects. [ABSTRACT FROM AUTHOR]

Understanding the locus of fluid flow along thrust and splay faults is important to understand the hydraulic properties of accretionary systems and fault mechanics. Here, we use rock magnetic techniques in combination with backscattered electron imaging to depict the locus of enhanced magnetic mineral alteration within the Pāpaku fault, an active splay fault of the subduction interface at the northern Hikurangi Margin. The Pāpaku fault was cored at Site U1518 during Expedition 375 of the International Ocean Discovery Program and we report room temperature magnetic parameters, complemented by first‐order reversal and thermomagnetic curves in the depth interval 250–400 m below seafloor (mbsf). The ∼60‐m wide Pāpaku fault zone comprises two main slip zones, referred to as the upper main brittle (304–321 mbsf) and lower subsidiary (351–361 mbsf) fault zones, and an intervening zoned, termed the lower ductile deformation zone. Two narrow zones, at the top of the main brittle fault zone, and one in a sand‐rich interval above the subsidiary fault zone, experienced enhanced magnetic mineral diagenesis, which resulted in the recrystallization of ferrimagnetic greigite to paramagnetic pyrite. We propose that secondary magnetic mineral diagenesis was driven by anaerobic methane oxidation within these intervals, which occurs in the presence of methane and sulfate. We relate the observed changes to the fault parallel transport of fluids which is restricted to two damage zones. Overlying compacted and clay‐rich sediments likely act as a barrier to upward advective flow through the fault zone and into the hanging wall. Key Points: We report the results of rock magnetic properties and backscattered electron investigations in a profile through a subduction splay faultEnhanced magnetic mineral diagenesis in two slip zones resulted in the neoformation of iron‐sulfide mineralsWe suggest that the accumulation and fault parallel transport of reactants in fracture zones allowed anaerobic methane oxidation to occur [ABSTRACT FROM AUTHOR]

The spin crossover salt [Fe(bpp)2](isonicNO)2⋅ 2.4 H2O (1⋅2.4 H2O) (bpp=2,6‐bis(pyrazol‐3‐yl)pyridine; isonicNO=isonicotinate N‐oxide anion) exhibits a very abrupt spin crossover at T1/2=274.4 K. This triggers a supramolecular linkage (H‐bond) isomerization that responds reversibly towards light irradiation or temperature change. Isotopic effects in the thermomagnetic behavior reveal the importance of hydrogen bonds in defining the magnetic state. Further, the title compound can be reversibly dehydrated to afford 1, a material that also exhibits spin crossover coupled to H‐bond isomerization, leading to strong kinetic effects in the thermomagnetic properties. [ABSTRACT FROM AUTHOR]

We conducted a geomagnetic paleointensity study of lava flows at ∼30 Ma distributed in the Lima‐Limo section of the Afro‐Arabian Large Igneous Province. The Tsunakawa‐Shaw method, which has built‐in low‐temperature demagnetization and double heating procedures, was applied to 120 specimens from 45 lava flows, successfully obtaining paleointensities from 75 specimens within 34 lava flows. We measured hysteresis loops and thermomagnetic curves to examine the influence of magnetic properties on the paleointensities but found no relationship between the paleointensities and the ratios of the hysteresis parameters. We calculated 27 flow‐level paleointensity means after excluding specimens that possibly contain titanomaghemite based on thermomagnetic curves. We observed cyclic changes of paleointensity in the lowest reversed magnetozone, which may reflect paleosecular variations. To estimate a representative virtual axial dipole moment (V(A)DM) at ∼30 Ma, we applied a flow‐level selection criterion depending on the specimen numbers. Eleven flow‐level means passed the criterion, which gave an averaged VADM of 4.2 ± 2.1 × 1022 Am2. This is similar to five averaged VADMs reported previously in the Late Cretaceous and the Cenozoic using the Tsunakawa‐Shaw method. We combined our data with available data between 25 and 35 Ma. We concluded that the mode of 4.4 × 1022 Am2 from 32 flow‐level means is representative of this period. This is close to two previously reported long‐term representative VADMs since the Jurassic. Key Points: We obtained paleointensities from the Afro‐Arabian Large Igneous Province and examined influence of magnetic propertiesA dipole moment mode from 25 to 35 Ma is estimated at 4.4 × 1022 Am2The geodynamo may have kept a time‐averaged dipole moment of ∼4 × 1022 Am2 since the Jurassic [ABSTRACT FROM AUTHOR]

Variably serpentinized peridotites from the Zedang ophiolite in southern Tibet were magnetically and petrologically examined to understand the serpentinization process and evaluate the origin of magnetic anomalies in ultramafic‐hosted tectonic settings. Magnetite occurs in the serpentine and brucite veins and is identified as the dominant magnetic carrier by thermomagnetic and petrological analyses. The magnetic susceptibility increases rapidly from <0.001 to ~0.02 SI for the <50% serpentinized samples followed by nearly constant values of 0.02–0.03 SI above 50% serpentinization. This transition corresponds with the formation of Fe‐poor serpentine mesh (2–3 wt% FeO) and magnetite in the early stages and the replacement of mesh center olivine by Fe‐rich serpentine (4–5 wt% FeO) without magnetite in the late stages. Brucite veins occur in the 50–70% serpentinized samples and indicate serpentinization temperatures from ~250 to <100°C. The serpentinization may initiate at an oceanic spreading ridge center under high temperatures (>250–300°C) to produce magnetite and subsequently continue at lower temperatures (<200–250°C) in near‐seafloor settings and limit the magnetite formation, possibly associated with ophiolite emplacement. These serpentinized peridotites have higher magnetization intensities (average 2.26 Am−1) than dolerite dykes and basaltic volcanics (mostly <1 A m−1) in the area and should be the major source of aeromagnetic highs in the south Tibetan ophiolite belt. Key Points: Variably serpentinized peridotites from the Zedang ophiolite in southern Tibet were magnetically and mineralogically examinedWe observed that magnetite formation is limited above ~50% serpentinization in the Zedang ophioliteThe serpentinization may start at >250–300°C at an oceanic spreading ridge center and continue at <200–250°C in near‐seafloor settings [ABSTRACT FROM AUTHOR]

This study investigates that the sound wave propagation of multiferroic thermo elastic Nanofibers under the influence of surface effect and parametric excitation via Timoshenko form of beam equations. The equation of analytical model is obtained for Nanofiber through shear and rotation effect. The solution of the problem is reached through the coupled time harmonic equations in flexural direction. Graphs are drawn for frequency, phase velocity, piezoelectric strain, magnetic field and dynamic displacement at different vibration modes of Nanofibers. From the result obtained, it is seen that the surface effect and excitation frequency gives significant contribution to the physical variables of the Nanofiber. The frequency grows in the presence of surface effect and decay as length increases both in Euler's and Timoshenko beam theory. Also, a comparison of numerical results is made with existing literature and good agreement is arrived. The present study is expected to be more helpful for the design of piezo-thermomagneto- mechanical Nanofiber-based devices. [ABSTRACT FROM AUTHOR]

The modern designs of magnetic field transducers (MFTs) based on nanostructures with the spin-tunnel magnetoresistive effect (STMR) and the main areas of their application are considered. The results of an experimental study of two constructive versions of magnetic field transducers with an even and odd output characteristic are presented. The sensitivity of the fabricated MFT model based on the STMR effect with an even output characteristic is 0.54 mV/(V Oe) in the range of a magnetic field with the intensity ranging from 0 to 40 Oe. The results of dependency conversion are presented. R(H) nanostructures with the STMR effect by thermomagnetic treatment to reduce hysteresis and increase linearity in the working range of the magnetic field. The sensitivity of the fabricated MFT model based on the STMR effect with an odd output characteristic is 5.4 mV/(V Oe) in the range of a magnetic field with a strength of ±1 Oe. In conclusion, promising directions of the development of magnetic field converter (MFC) structures based on nanostructures with the STMR effect are described. [ABSTRACT FROM AUTHOR]

Recent studies have pointed out that first-order magnetic transitions can be affected by defects. It however remains unclear which precise microstructural features are involved and how to pragmatically control their formation. Here, we show that a genuine technical parameter such as the compaction pressure employed prior to the sintering can induce subtle differences on magnetization data and yet correspond to a large evolution of the magnetocaloric performances in MnFe 0.95 P 0.575 Si 0.36 B 0.065 compounds prepared by powder metallurgy, resulting in an enhancement of the isothermal entropy change (Δ S) in 1 T up to ∼40 %. This outcome is unexpected as Δ S normalized per mass should not be affected by what is at first glance a matter of compaction or density. Our detailed structural and microstructural investigations indicate that the sharpening of the transition for the highest compaction pressures originate from different distributions of the secondary phase at the grain boundaries. This work not only bring into light an interesting fundamental question how microstructural details can affect the development of a magnetic transition, it has also important practical consequences to ensure a reproducibility of large magnetocaloric or thermomagnetic effects in MnFe(P,Si,B) materials for possible applications. [Display omitted] • Magnetocaloric performances of MnFe(P,Si,B) increase with higher green compaction. • Final density not affected by green pressure with common 24 h high temperature sintering. • Increase in ΔS is not related to secondary phase content but rather to its distribution. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect (ANE), one of the thermomagnetic effects studied for a long time, has recently attracted renewed attention. The ANE, which originates from fictitious fields in momentum space, is essential for clarifying the interplay among heat, spin, and charge in magnets. Moreover, compared to the Seebeck effect, it has various benefits for application to high-efficiency energy-harvesting devices as it may provide much more simple lateral structure, higher flexibility, and much lower production cost. In this review, we discuss various topics related to the methods to modulate the ANE for its thermoelectric applications. In addition, we review strategies to design materials to obtain large ANE including Weyl magnets and thermoelectric devices for effectively utilizing the ANE. [ABSTRACT FROM AUTHOR]

We studied the thermomagnetic power S ii (B) and Nernst–Ettingshausen effect S ij (B) in inclination bicrystals of Bi and 3D topological insulator Bi 1−x Sb x (0.04 < x ≤ 0.12) with superconducting nano-width interfaces (T c ≤ 21 K). High values of thermomagnetic effects in small disorientation angle (SDA) bicrystals far exceeding values in single-crystalline samples were found. It was established that S ii (B) linearly increases in high fields without saturation and change the sign from negative in positive in bicrystals of 3D Dirac point forming (x ∼ 0.04), specifying the signature of 3D topological semimetal. Contrarily, S ii (B) in LDA bicrystals with 0.06 ≤ x ≤ 0.12 undergoes saturation or increases smoothly, the Landau level index depends linearly on 1/ B n , and extrapolate to – 0.5 if 1/ B n → 0, what is typical for the 3D topological insulators. Two new quantum oscillation harmonics are reviled in high fields; they characterize different densities of electronic states and different levels of disorder at LDA and SDA interfaces. • The thermomagnetic effects in small inclination bicrystals with nano-width superconducting interfaces are considerably higher than in single crystals and large disorientation angle samples of Bi and Bi 1−x Sb x (0.04 ≤ x ≤ 0.12) alloys. • The inclination bicrystals of 3D Dirac point forming (x ∼ 0.04) show features of thermomagnetic transport characteristic of 3D topological semimetal. • The high magnetic field dependences of thermomagnetic power in Bi 1−x Sb x (0.06 ≤ x ≤ 0.12) bicrystals are typical for 3D topological insulators with massless Dirac fermions. • Two new quantum oscillation harmonics are reviled in high fields; they characterize different densities of electronic states and different levels of disorder at small and large inclination interfaces. [ABSTRACT FROM AUTHOR]

This paper aims at studying the effect of Mn2+ in MnxZn1−xFe2O4 (x = 0.3, 0.4, 0.5, 0.6, 0.7) ferrite nanoparticles (NPs) and ferrofluid (FF) prepared by chemical coprecipitation method. Structural studies were carried out using X-ray diffraction, fourier transform infra-red spectroscopy and morphological using high-resolution transmission electron microscopy. A vibrating sample magnetometer and electron paramagnetic resonance were employed to study the magnetic properties of prepared samples. It was observed that with increase in Mn content from x = 0.3 to 0.7, maximum magnetization showed increasing trend from 29.24 to 46.66 emu/g (at 2 T) with coercivity and retentivity almost equals to zero and Curie temperature from 380 to 522 K. A practical design of self-regulating cooling device has been constructed employing the synthesized FF as coolant. The device makes use of the dissipated heat and magnet to regulate the fluid flow in the loop exploiting the thermo-magnetic property of FF and transferring heat from heat load to sink. The device is self-powered, self-cooling, inexpensive and easy to maintain. By means of experiments performed, role of temperature of heat load, volume fraction of NPs and magnetic field strength has also been investigated and discussed. [ABSTRACT FROM AUTHOR]

Highlights • Ti fully dissolves in NiMnGa-based single phase structure. • Gd addition promotes dual-phase microstructure in the NiMnGa-based alloy. • Ti for Ga substitution leads to the decrease of the martensitic transition temperature. • Gd shifts the martensitic transition temperature to the room temperature regime. • Ti and Gd improved the mechanical properties of the NiMnGa-based alloy. Abstract The present study is focused on the influence of Ti and Gd doping at the Ga site on the microstructure, magnetic and mechanical properties of the polycrystalline Ni 50 Mn 25 Ga 20-x Z x (x = 0 or 5, Z = Gd, Ti) magnetic shape memory alloys. Microstructure investigations show that reference Ni 50 Mn 25 Ga 25 and Ti-doped alloys, both in the as-cast and annealed state, are single phase materials, whereas Gd-doped sample reveals dendritic dual-phase structure with substantial distinction between Gd-rich and Gd-poor regions. Thermomagnetic measurements expose reversible martensitic transition in the Ni 50 Mn 25 Ga 25 and Ni 50 Mn 25 Ga 20 Ti 5 alloys, where Ti addition to NiMnGa composition leads to the decrease of phase transformation temperature from T M = 193 K for reference sample to T M = 172.5 K for Ti-doped material. Furthermore, the Ni 50 Mn 25 Ga 20 Gd 5 alloy does not experience fully martensitic transition. Temperatures of magnetic transformation also varies with chemical composition and equals to 379 K, 318 K and 370 K for the annealed Ni 50 Mn 25 Ga 25 , Ni 50 Mn 25 Ga 20 Ti 5 and Ni 50 Mn 25 Ga 20 Gd 5 alloy, respectively. Mechanical properties investigation based on the nanoindentation measurements shows beneficial influence of doping elements on material hardness. In addition, planar distributions of hardness allow to deconvolute mechanical properties of each individual phase of the Ni 50 Mn 25 Ga 20 Gd 5 alloy. [ABSTRACT FROM AUTHOR]

Abstract It is usually claimed that structural and magnetic transitions should coincide to improve the total entropy change. Here we show that overlapping structural and magnetic transitions can compete with each other, which gives rise to some signature of the competition misinterpreted as an experimental artifact of the measurements as observed in Ni 49+x Mn 36-x In 15 (nominally x = 0, 0.5, 1.0, 1.5 and 2.0) investigated in this work. Their various magnetic phase transitions show a low temperature conventional magnetocaloric effect (MCE), an inverse MCE followed by another high temperature conventional MCE. For concurrent phase transitions with their respective transition temperatures close to one another, an observed spike embedded in the high temperature conventional MCE region is found arising from the martensitic transformation. We show that a crossover of the magnetic field dependence of the transition temperatures is obtained for concurrent phase transitions occurring in a narrow temperature range. As an evidence of the complexity of overlapping phase transitions, a recently proposed quantitative method for determining the order of phase transition is applied to this compositional series, showing its applicability even to cases when first- and second-order phase transitions occur in a narrow temperature range. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Thermomagnetic convection is a controlling phenomenon for heat-transfer in ferrofluids. It depends upon the magnetic field gradients, variation in magnetic susceptibility, particle concentration and temperature gradients. This article presents the effect of these parameters on cooling of a current carrying micro-wire in ferrofluid with a focus on magnetophoresis effects. A two-phase Euler-Euler model is developed. The predictions of this model are compared with experimental results and predictions from a single-phase ferrofluid model. For ferrofluid with volume fraction of φ = 0.02, the predicted average wire temperature from the Euler-Euler two-phase model is approximately 1 K lower than the measured wire temperature,while the single phase model is 5 K higher. Under identical magnetic field and heat flux conditions, variations in the particle concentration are found to have a non-negligible effect on thermomagnetic convective cooling. The maximum temperature of the wire for φ = 0.01 ferrofluid is significantly increased by 10 K and greater enhancement to cooling is observed in the case of φ = 0.04, where the inception of thermomagnetic cooling is advanced. Correspondingly, significantly different thermal and velocity fields are observed for different volume fractions. The simulations show different regimes of heat transfer. During the first few hundred milliseconds after applying electrical current, a thin boundary layer develops near the wire surface and the colder region is thermally stratified. At larger time, dispersion of ferro-particles between colder and hotter regions produces concentration gradients which affect the thermal and velocity fields. Eddies generated by thermomagnetic convection are found to form at the bottom of the vertical wire and retain their structure as they are convected upwards by natural convection. The particle concentration at the wire surface (φ w s) varies from 0.0188 to 0.0260 for an initial volume fraction (φ) of 0.02. This variation disturbs the thermal boundary layer and generates thermal vortices around the heated wire that differ from single-phase model predictions. • Validation of Two-Phase and Single-phase thermomagnetic model with experiment. • Variation in local concentration of ferroparticles around heated Cu-wire. • Plume-like flow structures for the higher concentration ferrofluid. • Continuous rising of thermal cells adjacent to the vertical wire. [ABSTRACT FROM AUTHOR]