High-temperature Magnetization Research Articles

Study on the high temperature magnetization reversal mechanism of grain boundary diffusion Nd–Fe–B sintered magnet by magnetic domain evolution observation

Nd–Fe–B sintered magnets with ultrahigh coericivity of 47.1 kOe and maximum energy product of 38.5 MGOe have been successfully prepared by TbH3 nanoparticles grain boundary diffusion (GBD) process. Microstructural observations show that Tb enriches in the outer regions of 2:14:1 matrix phase grains, forming a core–shell structure. High temperature magnetic domain evolution observations indicate that reversed domains tend to nucleate at the outer regions of 2:14:1 matrix phase grains at 200 °C, while the Tb-rich shells show high magnetocrystalline anisotropy improving the nucleation field at outer regions, leading to enhancement of high temperature magnetic performance.

Oxygen diffusion and vacancy migration thermally-activated govern high-temperature magnetism in ceria

Several experimental works currently demonstrate that metallic nano-oxides and carbon nanomaterials expected to be diamagnets, in fact, behave as ferromagnets at room temperature. More than scientifically intriguing, this unconventional and unexpected ferromagnetism pave the way for innovation products and novel nanotechnological applications, gathering the magnetism to interesting functionalities of these nanomaterials. Here, we investigate the non-conventional ferromagnetism observed at high temperatures in nanocrystalline cerium dioxide (CeO2or nanoceria) thin films that are optically transparent to visible light. Nanoceria exhibits several concrete applications in catalytic processes, photovoltaic cells, solid-state fuel cells, among others, which are mostly due to natural presence of oxygen vacancies and easy migration of the oxygen through the structure. The ferromagnetism in non-stoichiometric nanocrystaline ceria can be consistently described by ab initio electronic structure calculations, which support that oxygen vacancies cause the formation of magnetic moments and can provide a robust interconnectivity within magnetic polarons theoretical framework. Additionally, we present a conceptual model to account the oxygen transport to the non-conventional ferromagnetism at temperatures well above room temperature. The approach is complementary to the thermally-activated effective transfers of charge and spin around oxygen vacancy centers.

Fabrication of MnBi alloys with high ferromagnetic phase content: effects of heat treatment regimes and dopants

The low-cost and rare-earth-free MnBi alloys were focused for investigation during last 5 years as a promising alternative for high-cost rare-earth-containing Nd–Fe–B in high-temperature permanent magnet applications. Because of the peritectic nature of solidification, MnBi alloys containing high ferromagnetic phase content could not be easily prepared for massive scale. In this paper, the roles of heat treatment regimes including the zone-travelling under temperature gradient, multi-time annealing (MTA) and the doping soft ferromagnetic Fe65Co35 phase in preparing MnBi alloys with high ferromagnetic phase content were investigated. The results showed that, for the case of applying the temperature gradient assisted zone-travelling technique, the ferromagnetic phase content in prepared alloys reached 85 wt%. By using the MTA technique, the ferromagnetic phase content is raised up 96 wt% when MnBi alloys were annealed three times at 300 °C for 20 h. The doping of Fe65Co35 as a soft ferromagnetic phase stabilized the ferromagnetic phase in the obtained MnBi1−x(Fe65Co35)x alloys (x = 0.1, 0.2, 0.3) with the magnetization measured at 13.5 kOe of 63.1, 70.8 and 80.5 emu/g, respectively.

Intrinsic Half‐Metallicity in 2D Ternary Chalcogenides with High Critical Temperature and Controllable Magnetization Direction

AbstractSearching for 2D ferromagnetic materials with a high critical temperature, large spin polarization, and controllable magnetization direction is a key challenge for their broad applications in spintronics. Here, through a systematic study on a series of 2D ternary chalcogenides with first‐principles calculations, it is demonstrated that a family of experimentally available 2D CoGa2X4 (X = S, Se, or Te) are half‐metallic ferromagnets, and they exhibit high critical temperature, fully polarized spin state, and strain‐dependent magnetization direction simultaneously. Following the Goodenough–Kanamori rules, the half‐metallic ferromagnetism of CoGa2X4 family is caused by superexchange interaction mediated by CoXCo bonds. The half‐metal gaps are large enough (>0.5 eV) to ensure that the half‐metallicity is stable against the spin flipping at room temperature. Magnetocrystalline anisotropy energy calculations indicate that CoGa2X4 favor easy plane magnetization. Under achievable biaxial tensile strain (2–6%), the magnetization directions of CoGa2X4 can change from in‐plane to out‐of‐plane, providing a route to control the efficiency of spin injection/detection. Further, the critical temperatures Tc of ferromagnetic phase transition for CoGa2X4 are close to room temperature. Belonging to the big family of layered AB2X4 compounds, the proposed CoGa2X4 systems will enrich the available 2D candidates and their heterojunctions for various applications.

Effect Laws of Different Factors on Levitation Characteristics of High-Tc Superconducting Maglev System with Numerical Solutions

The interaction between the high-temperature superconducting (HTS) bulk and permanent magnet guideway (PMG) has been a topic among the existing HTS magnetic levitation systems. Up to now, the theories about the electromagnetic and force characteristics have been relatively consummated. Here, using the finite element model by COMSOL Multiphysics 5.3a, we investigated the impact of the intrinsic and external factors on the levitation characteristics of HTS maglev systems, the application laws are concluded. Factors including the critical current density and geometric dimensions of the bulk superconductor, as well as the moving velocity, are discussed. The effects of the multiple back and forth movements are also analyzed. By comparing calculation results of the distributions of the induced current and the levitation force of the bulk superconductor, we can clearly confirm the effect laws of various factors on the electromagnetic characteristics and levitation force. These observations support the physical parameters that are difficult to be tested by experiments. And they also have a significant contribution to the experimental condition selections and optimization of the high-temperature superconducting magnetic levitation.

A Paleomagnetic Study of Sariolian Conglomerates of the Onega Structure of the Karelian Protocraton: The Problem of Global Paleoproterozoic Remagnetization

A paleomagnetic study of Sariolian (2.4–2.3 Ga) conglomerates of the Onega structure distinguished two characteristic magnetization components. The average direction of the mid-temperature magnetization component has a concentrated distribution and coincides with the direction of the Svecofennian remagnetization within the Karelian protocraton. The directions of high-temperature magnetization components distinguished in conglomerates show a wide scatter of values that is evidence of the primary origin of this magnetization component. Two clusters of high-temperature components associated not only with the protolith composition, but also with the different conditions of rock transformation, in particular their fluid saturation, are distinguished.

Paleomagnetic studies sariolyiski conglomerates of the Onega structure of the Karelian craton: Paleoproterozoic global remagnetization

As a result of paleomagnetic studies Sariolian 2,4–2,3 Ga conglomerates of the Onega basin of the Karelian protoctaton, two characteristic components of magnetization have been separated. Mean direction of the medium-temperature component has a heap distribution and coincides with mean direction of the Svecofennian remagnetization within the Karelian protocraton. The directions of high-temperature magnetization components isolated in conglomerates have a significant spread, which indicates the primary nature of this magnetization component. Two clusters of high-temperature components associated not only with the composition of protolites, but also with different conditions of rock transformations, including their fluid saturation, are distinguished.

A New Paleomagnetic Pole for the Silurian Geological Sequences of Tuva

New paleomagnetic data are determined for Silurian rocks of Tuva. One-, two-, and three-component magnetization is distinguished for the rocks. The low-temperature (LT) components of magnetization were close to the directions of the present-day or Cenozoic magnetic field of Tuva. The prefold high-temperature (HT) magnetization is considered close to primary as a result of fold and reversal test. Its age is almost identical to the age of the formation of Silurian rocks, which were formed at 20–30° N. The Silurian paleomagnetic pole calculated can be used to describe the movement of the Caledonian block of Central Asia as well as probably of Siberia, if these blocks were combined tectonically prior to the Silurian. It is characterized by Φ = 4.6, Λ = 146, and А95 = 6.8.

Structural, Magnetic, and Mössbauer Studies of Transition Metal-Doped Gd2Fe16Ga0.5TM0.5 Intermetallic Compounds (TM = Cr, Mn, Co, Ni, Cu, and Zn)

The effect of transition metal substitution for Fe and the structural and magnetic properties of Gd2Fe16Ga0.5TM0.5 (TM = Cr, Mn, Co, Ni, Cu, and Zn) compounds were investigated in this study. Rietveld analysis of X-ray data indicates that all the samples crystallize in the hexagonal Th2Ni17 structure. The lattice parameters a, c, and the unit cell volume show TM ionic radii dependence. Both Ga and TM atoms show preferred site occupancy for 12j and 12k sites. The saturation magnetization at room temperature was observed for Co, Ni, and Cu of 69, 73, and 77 emu/g, respectively, while a minimum value was observed for Zn (62 emu/g) doping in Gd2Fe16Ga0.5TM0.5. The highest Curie temperature of 590 K was observed for Cu doping which is 15 and 5% higher than Gd2Fe17 and Gd2Fe16Ga compounds, respectively. The hyperfine parameters viz. hyperfine field and isomer shift show systematic dependence on the TM atomic number. The observed magnetic and Curie temperature behavior in Gd2Fe16Ga0.5TM0.5 is explained on the basis of Fe(3d)-TM(3d) hybridization. The superior Curie temperature and magnetization value of Co-, Ni-, and Cu-doped Gd2Fe16Ga0.5TM0.5 compounds as compared to pure Gd2Fe17 or Gd2Fe16Ga makes Gd2Fe16Ga0.5TM0.5 a potential candidate for high-temperature industrial magnet applications.

A new Siberian record of the ∼1.0 Gyr-old Maya superchron

We report new magnetostratigraphic data from the Late Mesoproterozoic Linok Formation consisting of clayed carbonates, together with paleomagnetic data from the Neoproterozoic carbonate Sukhaya Tunguska, Burovaya and Turukhansk formations, located in the Turukhansk region (northwestern Siberian platform). We also re-analyzed demagnetization data previously obtained from the Derevnya Formation. Paleomagnetic analyses revealed up to four magnetization components. First, a steep-inclination component, likely of recent origin, is isolated in all sections in the low temperature range. Second, a magnetization is recovered in most samples between ∼250 °C and ∼350–400 °C. It shows a single magnetic polarity and is interpreted as a remagnetization acquired during the Kiaman Permo-Carboniferous reverse superchron. Third, a magnetization component is isolated between ∼400 °C and ∼500 °C in samples from the Burovaya and Turukhansk formations. This component is interpreted as a remagnetization that occurred before the end of the Neoproterozoic. A fourth high-temperature (HT) magnetization component is observed up to ∼575 °C in samples from the Linok and Burovaya formations and up to ∼680 °C for those of the Derevnya and Turukhansk formations. A series of magnetic polarity reversals is observed in the lower and middle parts of the Linok Formation, whereas a single polarity interval is found in its upper part. The syn-depositional origin of this magnetization is attested by positive reversal, conglomerate and fold tests. The HT magnetization component isolated in the Derevnya and Burovaya formations shows a single magnetic polarity. Its primary origin is supported by the fact that the Derevnya and Burovaya HT mean directions are positioned in the continuity of the directional evolution observed through the Linok Formation. It is further constrained by very consistent Late Mesoproterozoic to Early Neoproterozoic apparent polar wander paths obtained from different regions of the Siberian platform. A single magnetic polarity reversal is observed in a ∼40 m-thick section of the Turukhansk Formation. The HT directions found in the upper part of the Linok Formations, over a stratigraphic thickness of ∼200 m, and in the Derevnya and Burovaya formations strengthen the existence of the normal polarity Maya superchron around 1.0 Ga, at the transition between the Mesoproterozoic and the Neoproterozoic.

Structure and Magnetic Properties of Heat-Resistant Sm(Co0.796−xFe0.177CuxZr0.027)6.63 Permanent Magnets with High Coercivity

The structure and temperature stability of high-temperature permanent magnets Sm(Co0.796−xFe0.177CuxZr0.027)6.63 (x = 0.117 and 0.130) were studied using x-ray diffraction analysis, thermomagnetic analysis, and scanning and transmission electron microscopy. The magnets have a nanocrystalline cellular structure composed of the R2:17 cell phase, 1:5 boundary phase (27–28% by volume), and Z-phase platelets. The 1:5 phase is formed in the course of isothermal annealing at 850°C and exists in the entire temperature range from 850°C to 400°C. The Curie temperature of the R2:17 and 1:5 phases is approximately 815°C and 580°C, respectively. The magnets have the following hysteresis properties at room temperature: Br = 890–920 mT, JHc = 2.4–2.6 MA/m, BHc = 629–676 kA/m, and (BH)m = 143–159 kJ/m3. In the temperature range of 20–500°C, the temperature coefficients of Br and JHc of the magnets (x = 0.117 and 0.130) do not exceed |− 0.070| and |− 0.172|%/°C, respectively.

Structure and Properties of Sm – Co – Fe – Cu – Zr Magnets for High-Temperature Applications

Sm – Co – Fe – Cu – Zr sintered high-temperature permanent magnets (HTPM) produced by the “POZ-Progress” Company are studied. The microstructure of the magnets is determined by scanning electron microscopy and x-ray diffraction analysis. The Curie temperature and the magnetic properties of the materials are described. The hysteresis loops of the magnets are measured in strong pulsed fields at room and elevated temperatures. The temperature dependence of the magnetic susceptibility is plotted using the method of compensated transformer in a variable magnetic field.

Comparison of shear strength and failure mechanisms of lap joint between REBCO tapes bonded by different joining techniques

Lap joints between Rare-Earth Barium Copper Oxide (REBCO) tapes are intended to be employed for segmented fabrication of high-temperature superconducting magnet as innovative design of fusion magnets. This study evaluates the shear strength and failure mechanism of lap joints between commercial REBCO tapes from two different manufacturers while using different mechanical joining procedures or soldering alloys. Additionally, the shear strength along the width direction of the different REBCO tapes was experimentally evaluated. Overall results using REBCO tapes with soldered Cu stabilizer revealed that they are unsuitable for field application due to low shear strength of the tapes. On the other hand, REBCO tapes with electro-plated Cu stabilizer are more versatile; soldered lap joints using Pb37Sn63 showed shear strength higher than required value. However, failure mechanism of the soldered joints always involve delamination of the REBCO tape which instantly increase joint resistance. Conversely, mechanical lap joints with indium fabricated using the improved method with heat treatment or indium pre-coating with heat treatment exhibited cohesive failure followed by plastic deformation of indium, which reduces the shear stress while maintaining acceptable joint resistance. This fact makes the mechanical lap joint a more reliable option so far.

Structure elucidation capabilities on typical pharmaceutical drugs by new nuclear magnetic resonance technology: a 400 MHz high-temperature superconducting power-driven magnet NMR system

Nuclear magnetic resonance (NMR) is a powerful technique for the structure elucidation of organic molecules and significantly important in the pharmaceutical industry supporting the discovery and development of drug substances or active pharmaceutical ingredients (APIs). Following an initial study and assessment of a prototype NMR instrument with a high-temperature superconducting (HTS) power-driven magnet of 9.4 T (400 MHz for 1H observation) operating with standard commercial electronics and probes, we tested the instrument with three compounds representing typical pharmaceutical drugs. We compared results from two probes and shimstacks with different geometries (broadband fluorine observe (BBFO) with Bruker orthogonal shim system-3 (BOSS3) and Bruker quattro nucleus probe (QNP) with BOSS1 shims) testing standard one-dimensional (1D) NMR experiments including selective excitation experiments, and two-dimensional (2D) homonuclear and heteronuclear experiments for the purposes of evaluating the equipment for structure elucidation capabilities. In our initial study on cinacalcet HCl, only the 1D 1H experiment showed a loss of resolution when using the longer coiled BBFO probe with the BOSS3 shims compared to the shorter coiled QNP probe with BOSS1 shims. The selective excitation experiments using the cinacalcet HCl were successful. Our characterization of 1D (1H, 13C, 19F) and 2D (1H-1H and 1H-13C) NMR experiments for compounds I and II with the two probes and shimstacks indicated no significance differences. Overall, these results are satisfactory with the HTS magnet at the field of 9.4 T for the structural elucidation work of standard pharmaceutical compounds. This new technology has the advantage of being able to locate the HTS NMR magnet system in any chemistry or analytical laboratory where the samples are produced, facilitating rapid analysis with minor needs from the facilities and without cryogenic liquids.

Systematics of Early Cambrian Paleomagnetic Directions from the Northern and Eastern Regions of the Siberian Platform and the Problem of an Anomalous Geomagnetic Field in the Time Vicinity of the Proterozoic–Phanerozoic Boundary

Representative paleomagnetic collections of Lower Cambrian rocks from the northern and eastern regions of the Siberian platform are studied. New evidence demonstrating the anomalous character of the paleomagnetic record in these rocks is obtained. These data confidently support the hypothesis (Pavlov et al., 2004) that in the substantial part of the Lower Cambrian section of the Siberian platform there are two stable high-temperature magnetization components having significantly different directions, each of which is eligible for being a primary component that was formed, at the latest, in the Early Cambrian. The analysis of the world’s paleomagnetic data for this interval of the geological history shows that the peculiarities observed in Siberia in the paleomagnetic record for the Precambrian–Phanerozoic boundary are global, inconsistent with the traditional notion of a paleomagnetic record as reflecting the predominant axial dipole component of the geomagnetic field, and necessitates the assumption that the geomagnetic field at the Proterozoic–Phanerozoic boundary (Ediacaran–Lower Cambrian) substantially differed from the field of most of the other geological epochs. In order to explain the observed paleomagnetic record, we propose a hypothesis suggesting that the geomagnetic field at the Precambrian–Cambrian boundary had an anomalous character. This field was characterized by the presence of two alternating quasi-stable generation regimes. According to our hypothesis, the magnetic field at the Precambrian–Cambrian boundary can be described by the alternation of long periods dominated by an axial, mainly monopolar dipole field and relatively short epochs, lasting a few hundred kA, with the prevalence of the near-equatorial or midlatitude dipole. The proposed hypothesis agrees with the data obtained from studies of the transitional fields of Paleozoic reversals (Khramov and Iosifidi, 2012) and with the results of geodynamo numerical simulations (Aubert and Wicht, 2004; Glatzmayer and Olson, 2005; Gissinger et al., 2012).

Temperature stability of SmCo (2:17) magnets modified by Ni–Cr two-layer coating

The oxidation resistance behavior of SmCo (2:17)-type high-temperature magnets modified with Ni–Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and Ni–Cr-modified magnets oxidized at high temperature (500 °C) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is 6.95 mg·cm−2 which is more than that (0.08 mg·cm−2) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction (XRD) and electron probe microanalysis (EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.

Fabrication of a new superparamagnetic metal-organic framework with core-shell nanocomposite structures: Characterization, biocompatibility, and drug release study

The Superparamagnetic CoFe2O4NPs@Mn-Organic Framework core-shell nanocomposites that had potential application in targeted drug-delivery were synthesized by layer to layer method. The structure and composition of the obtained microspheres were characterized by SEM, TEM, DLS, XRD, VSM, FTIR, and TG analysis. Results showed that the structures have a high degree crystalline, high temperature stability, magnetics and core-shell nanocomposites. Therefore, it is an excellent candidate for drug delivery systems. Afterwards, Daunorubicin (as a drug model) was laden in the MOFs by a Simple stirring. For comparison of magnetic properties of MOFs for drug delivery, an external magnetic field applied to the plate to evaluate the efficiency. The external magnetic field significantly increases anti-tumor activity of formulation (drug+ MOFs). The results showed that MOFs are biocompatible, which endue MOFs great potential in targeting drug-delivery systems with enhanced efficiency.

Relationship Between Orogenic Gold Mineralization and Crustal Shearing Along Ailaoshan‐Red River Belt, Southeastern Tibetan Plateau: New Constraint From Paleomagnetism

AbstractA new perspective on the relationship between orogenic gold mineralization and crustal shearing is presented in this case study on the gold deposits along Ailaoshan‐Red River shear zone (ARSZ), southeastern Tibetan Plateau. The sinistral ductile shearing along the zone occurred from ca. 31 to 17 Ma resulting in a displacement of ~1,000 km. A series of orogenic gold deposits, represented by the Zhenyuan and Chang'an deposits, occur on western margin of the ARSZ. The timing of mineralization and its relationship to shearing continues to be debated despite extensive geological and geochemical studies. Here we try to clarify this issue by using paleomagnetism to constrain the paleolatitude of mineralized rocks. High temperature magnetization components were isolated from the mineralized rocks, and they record modification by ore‐forming fluid. Their magnetization yields a paleolatitude of 19.9° ± 3.6°N for the Zhenyuan deposit and 16.2° ± 2.9°N for the Chang'an deposit. The paleolatitudes from these deposits are similar to those of ca. 20 Ma strata (19.0° ± 3.6°N), deposited after the large‐scale shearing. By contrast, they differ significantly from the paleolatitude obtained from ca. 130 to 40 Ma strata (28.4° ± 1.1°N), which formed long before the onset of large‐scale shearing. These observations imply that the orogenic gold mineralization occurred after the main offset and associated ductile deformation of the ARSZ. Gold mineralization is thought to be related to ore‐forming fluids and metals derived from the subcrust, rather than from fluids released from shearing‐induced metamorphism of regional strata.

Numerical Multiscale Model for AC Loss Calculation of Large-Scale HTS Solenoid Magnets

A numerical multiscale model is used for the calculation of ac loss in a two-dimensional (2-D) planar model and proves advantageous with regard to time and memory requirements. In this study, we improve the calculation accuracy and apply a multiscale model to a 2-D axisymmetric model of a high-temperature superconducting solenoid magnet by using an iteration method for the background field estimation. The calculation results are compared with those of the H-formulation model, homogenization model, and multiscale model with a J 0 uniform background field estimation method. The iteration method speeds up the calculation by 7.7 to 12.9 times and reduces the error of the average ac loss to 6.71% and the error of the ac loss peak value to 5.95%. In addition, the iteration method is superior to the homogenization model in terms of calculation speed and accuracy as the computational complexity increases.

Modifying the Pulsed-Field-Magnetization Technique for HTS Bulks in Electrical Machines Without Magnetic Field Sensors

This paper studies the high-temperature superconductor (HTS) YBCO and GdBCO bulks pulse-field magnetization (PFM) in loco , that is, when inserted in an electric machine's magnetic circuit. The PFM typically uses cryogenic hall sensors to monitor the magnetization process. However, to install cryogenic hall sensors in the magnetic excitation circuit of an electrical machine may increase the air gap and increase the machine cost. To surpass that, this paper presents an indirect technique capable of monitoring the superconductor magnetization process through the applied pulse voltage and associated electric current transient waveform. Last, different levels and the numbers of pulses were applied to magnetize the HTS bulks inside the magnetic circuit to analyze the resultant trapped magnetic field. Differences between the YBCO and GdBCO are highlighted and discussed.