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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]

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]

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]

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]

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]

Magnetic properties and microstructure of directly quenched Nd9.5Fe72.5-yTi2.5Zr0.5CryB15-xCx (x =0-1; y=0-3) magnets with a diameter of 1.1 mm and a length of 15 mm have been investigated. The thermomagnetic analysis show that the bulk magnets with x⩽0.5 and y=0-3 mainly consist of magnetically hard 2:14:1 phase. Besides, a slight substitution of C for B and Cr for Fe in Nd9.5Fe72.5-yTi2.5Zr0.5B15 can effectively refine the grain size of the bulk magnet with larger diameter, resulting in the remarkable enhancement of the magnetic properties. The optimal magnetic properties of Br=5.9 kG, iHc=8.2 kOe, and (BH)max=7.2 MGOe could be attained in Nd9.5Fe71.5-yTi2.5Zr0.5Cr1B14.5C0.5 magnet. [ABSTRACT FROM AUTHOR]

The current stimulated atomic diffusion in YBa2Cu3O7–δ superconducting bridges is investigated. A superconductor to insulator transition can be induced by the current controlled electromigration process, whereas the partial recovery of the superconducting state can be achieved by inverting the polarity of the bias. Interestingly, the temperature dependence of the current density JEM(T), above which atomic migration takes place, intersects the critical current density Jc(T) at certain temperature T*. Therefore, for T < T*, the current-induced dissipative state cannot be accessed without leading to irreversible modifications of the material properties. This phenomenon could also lead to the local deterioration of high critical temperature superconducting films abruptly penetrated by thermomagnetic instabilities. [ABSTRACT FROM AUTHOR]

In this paper, the crystallographic, magnetic, thermomagnetic, and magnetocaloric properties of the quenched NiMn1−xCrxGe (x = 0.04, 0.18, and 0.25) half-Heusler alloys have been studied by x-ray diffraction, differential scanning calorimetry and magnetization measurements. An influence of partial substitution of Cr for Mn and quenching of the samples on the character of structural and magnetic phase transitions is presented. Quenching of the alloys results in the formation of two phase (orthorhombic and hexagonal) crystal structure. The magnetic properties were investigated by means of magnetization measurements over a wide temperature (5–400 K) and magnetic field (up to 60 kOe) ranges. The experimental data indicate that at quenching and with increasing Cr content the magnetic order changes from antiferromagnetic to ferromagnetic. Hardened compounds exhibit a thermal hysteresis in the vicinity of the magnetic phase transition, what is characteristic for a first-order magnetic phase transition. The magnetic phase transition temperatures are decreased as a result of quenching of the samples. The magnetic entropy changes were calculated using the field dependences of isothermal magnetization in terms of the thermodynamic Maxwell relation. The magnetic entropy changes, |ΔSMmax|, obtained for the hardened alloys with x = 0.25 have the maximum value equal to 23 J/(kg·K) near the magnetic phase transition for a field change of ΔH = 0–60 kOe. [ABSTRACT FROM AUTHOR]

Stability of the vortex matter—magnetic flux lines penetrating into the material—in type-II superconductor films is crucially important for their application. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger an electromagnetic breakdown. In this paper, we review recent theoretical and experimental results on development of the above mentioned thermomagnetic instability. Starting from linear stability analysis for the initial critical-state flux distribution we then discuss a numerical procedure allowing to analyze developed flux avalanches. As an example of this approach we consider ultra-fast dendritic flux avalanches in thin superconducting disks. At the initial stage the flux front corresponding to the dendrite's trunk moves with velocity up to 100 km/s. At later stage the almost constant velocity leads to a specific propagation regime similar to ray optics. We discuss this regime observed in superconducting films coated by normal strips. Finally, we discuss dramatic enhancement of the anisotropy of the flux patterns due to specific dynamics. In this way we demonstrate that the combination of the linear stability analysis with the numerical approach provides an efficient framework for understanding the ultra-fast coupled nonlocal dynamics of electromagnetic fields and dissipation in superconductor films. [ABSTRACT FROM AUTHOR]

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS2 is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearly commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS2, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW→NCCDW transition. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect in a perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO thin film is measured using well-defined in-plane temperature gradients. The anomalous Nernst coefficient reaches 1.8 μV/K at room temperature, which is almost 50 times larger than that of a Ta/Co20Fe60B20/MgO thin film with perpendicular magnetic anisotropy. The anomalous Nernst and anomalous Hall results in different sample structures revealing that the large Nernst coefficient of the Ir22Mn78/Co20Fe60B20/MgO thin film is related to the interface between CoFeB and IrMn. [ABSTRACT FROM AUTHOR]

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS2 is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearly commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS2, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW→NCCDW transition. [ABSTRACT FROM AUTHOR]

The results of experimental studies of magnetic flux dynamics in finite-size superconductors, obtained using integral and local measurements methods, are presented. Local methods were aimed at clarifying the role of the demagnetizing factor in the dynamic formation of a complex magnetic structure of the critical state of hard superconductors. To understand the reasons for drastic transformation of the magnetic induction, we further analyzed the literature data on the visualization of flux dynamics in the presence of avalanches, obtained by magneto-optical methods. New features in the behavior of the magnetic flux during and after an avalanche were revealed and characterized: two stages in the formation of the magnetic induction distribution inside the avalanche region were established-homogeneous and heterogeneous filling with magnetic flux; the mechanism of inversion of the induction profile; velocity oscillations in the propagating magnetic flux front; transformation of the critical state band near the edge of the sample; and the role of the thermal effects and demagnetizing factor in the dissipative flux dynamics. The generalized information allowed us to present, within the framework of the Bean concept, a model of the transformation of the patterns of magnetic induction in the critical state and superconducting currents in a finite superconductor occurring as a result of flux avalanches in two different regimes--shielding and trapping of magnetic flux. [ABSTRACT FROM AUTHOR]

Thermomagnetic avalanches in superconducting films propagating extremely fast while forming unpredictable patterns, represent a serious threat for the performance of devices based on such materials. It is shown here that a normal-metal frame surrounding a selected region inside the film area can provide efficient protection from the avalanches during their propagation stage. Protective behavior is confirmed by magneto-optical imaging experiments on NbN films equipped with Cu and Al frames, and also by performing numerical simulations. Experimentally, it is found that while conventional flux creep is not affected by the frames, the dendritic avalanches are partially or fully screened by them. The level of screening depends on the ratio of the sheet conductance of the metal and the superconductor in the resistive state, and for ratios much larger than unity the screening is very efficient. [ABSTRACT FROM AUTHOR]

We report an alternative FeCrCoNiGe magnetic material based on FeCrCoNi high-entropy alloy with Curie point far below the room temperature. Investigations are done using first-principles calculations and key experimental measurements. Results show that the equimolar FeCrCoNiGe system is decomposed into a mixture of face-centered cubic and body-centered cubic solid solution phases. The increased stability of the ferromagnetic order in the as-cast FeCrCoNiGe composite, with measured Curie temperature of 640K, is explained using the exchange interactions. [ABSTRACT FROM AUTHOR]

Typically, the dynamic behaviour of magnetic nanoparticles is investigated by measuring their response to externally applied magnetic fields. In contrast, we present a study of the magnetic fluctuations in an ensemble of magnetic nanoparticles recorded in the absence of any external excitation. Several samples of magnetic nanoparticles with varying particle size, composition, and environment were investigated. We interpret the thermal magnetic noise spectrum to estimate particle size distributions and compare these to the distributions derived from magnetorelaxometry measurements of the same samples. [ABSTRACT FROM AUTHOR]

Material dependence of the anomalous Nernst effect (ANE) in perpendicularly magnetized ordered-alloy thin films is systematically investigated. The ANE was found to have a tendency to increase simply as uniaxial magnetic anisotropy increased at room temperature. The ANE increases as temperature increases from 10 to 300K for all the materials. However, the signs of the ANE in Fe-based ordered-alloys (L10-FePt and L10-FePd) and in a Co/Ni multilayer are opposite to those in Mn-based ordered-alloys (L10-MnGa and D022-Mn2Ga). Ordered-alloys with larger uniaxial magnetic anisotropies reveal larger ANE and might be desirable for thermoelectric applications. [ABSTRACT FROM AUTHOR]

A graded distribution of antidots in superconducting a-Mo79Ge21 thin films has been investigated by magnetization and magneto-optical imaging measurements. The pinning landscape has maximum density at the sample border, decreasing linearly towards the center. Its overall performance is noticeably superior than that for a sample with uniformly distributed antidots: For high temperatures and low fields, the critical current is enhanced, whereas the region of thermomagnetic instabilities in the field-temperature diagram is significantly suppressed. These findings confirm the relevance of graded landscapes on the enhancement of pinning efficiency, as recently predicted by Misko and Nori [Phys. Rev. B 85, 184506 (2012)]. [ABSTRACT FROM AUTHOR]

An intrinsic spin-dependent Seebeck effect in the linear tunneling transport regime of magnetic tunneling junctions (MTJs) was discovered recently. This effect leads to a nonlinear correction of Ohm's law in the dc response. We analyze this intrinsic magneto-thermoelectrical effect for MTJs with different MgO barrier (tb=0.7-1.35 nm) thicknesses. We report strong intrinsic effects in MTJs with thin MgO barriers (1189%), upon reversal of the magnetization of the two CoFeB layers. Such large effects are promising for useful spin caloritronic devices, integrating charge, heat, and spin tunnel transport. [ABSTRACT FROM AUTHOR]

Magnetic, magnetocaloric, and exchange bias properties have been systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic field along in-plane (IP) and perpendicular out of plane (OP) to the ribbon plane. From the thermo-magnetization curves, the sharpness of the martensitic transition is observed to be nearly the same for both IP and OP ribbons. The thermomagnetic irreversibility region is found to be larger in the OP ribbon at 500 Oe, indicating that the magnetic anisotropy is larger in this case. The OP ribbon shows the Hopkinson maximum at 500 Oe, both for the field cooled cooled and zero field cooled modes. The magnetization curve for IP ribbon shows a faster approach to saturation, compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has been found to be nearly same for both the ribbons. At 5 K, the coercivity and exchange bias values are larger for the OP ribbon. Crystallographic texturing of the ribbons and its effect in the easy magnetization direction are found to be the reason behind the differences between the two ribbons. [ABSTRACT FROM AUTHOR]

It is demonstrated that circular holes in superconducting films of Nb can arrest the propagation of thermomagnetic avalanches. The effect was found over a range of temperatures where the material is susceptible to this instability. For other hole shapes, like square and triangular, the sharp corners provoke secondary avalanches, thus extending the breakdown. Making use of circular stop-holes can become a practical way to limit thermomagnetic breakdown in superconducting films. [ABSTRACT FROM AUTHOR]