High-field Hysteresis Research Articles

Giant Magnon-Polaron Anomalies in Spin Seebeck Effect in Double Umbrella-Structured Tb_{3}Fe_{5}O_{12} Films.

We report a giant hysteretic spin Seebeck effect (SSE) anomaly with a sign reversal at magnetic fields much stronger than the coercive field in a (001)-oriented Tb_{3}Fe_{5}O_{12} film. The high-field SSE enhancement reaches 4200% at approximately 105K over its weak-field value and presents a nonmonotonic dependence on temperature. The unexpected high-field hysteresis of SSE is found to be associated with a magnetic transition of double-umbrella spin texture in TbIG. Nearly parallel dispersion curves of magnons and acoustic phonons around this neoteric transition are supported by theoretical calculations, leading to a high density of field-tuned magnon polarons and consequently an extraordinarily large SSE. Our study provides insight into the evolution of magnon dispersions of double-umbrella TbIG and could potentially boost the efficiency of magnon-polarons SSE devices.

Achieving low field-induced large strain by La-Nb co-doping in PZST-based anti-ferroelectric ceramics for high-performance actuators

Anti-ferroelectric (AFE) dielectrics are promising for actuators due to their large strain resulting from the phase transition from AFE phase to ferroelectric (FE) phase. However, their high phase transition electric field and strain hysteresis (Hs) limit their application in actuators. In this work, La-Nb co-doping in Pb(Zr0.85Sn0.08Ti0.07)O3 AFE ceramics realizes collaborative optimization of AFE-FE phase transition electric field (EAFE-FE), Hs and strain. La3+ ions replace Pb2+ ions to weaken long-range FE coupling and refine hysteresis loops. Nb5+ ions replacing B-site ions enhance the stability of FE phase in PZST ceramics, hence further reducing EAFE-FE. Furthermore, doping Nb5+ decreases grain size, which is conducive to producing higher field-induced strains. As a result, EAFE-FE decreases from 119 kV cm−1 to 47 kV cm−1 and Hs decreases from 75 % to 44 %, while strain remains at 0.47 %. The results demonstrate that La-Nb co-doping strategy promotes the application of large-strain AFE materials in actuators.

Second-Harmonic Response in Magnetic Nodal-Line Semimetal Fe3GeTe2

We experimentally investigate second-harmonic transverse voltage response to ac electrical current for a magnetic nodal-line semimetal Fe3GeTe2 (FGT). For zero magnetic field, the observed second-harmonic voltage behaves as a square of the longitudinal current, as it should be expected for nonlinear Hall effect. The magnetic field behavior is found to be sophisticated: while the first-harmonic response shows the known anomalous Hall hysteresis in FGT, the second-harmonic Hall voltage is characterized by the pronounced high-field hysteresis and flat (B-independent) region with curves touching at low fields. The high-field hysteresis strongly depends on the magnetic field sweep rate, so it reflects some slow relaxation process. For the lowest rates, it is also accomplished by multiple crossing points. Similar shape of the second-harmonic hysteresis is known for skyrmion spin textures in nonlinear optics. Since skyrmions have been demonstrated for FGT by direct visualization techniques, we can connect the observed high-field relaxation with deformation of the skyrmion lattice. Thus, the second-harmonic Hall voltage response can be regarded as a tool to detect spin textures in transport experiments.

Enhanced energy storage performance of 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3 lead-free relaxor ceramic by composition design strategy

Dielectric ceramic capacitors with high energy density are one of the great bright energy storage devices. Here, the Bi0.5Na0.5TiO3, 0.75Bi0.5Na0.5TiO3-0.25SrTiO3, 0.65Bi0.5Na0.5TiO3-0.35SrTiO3 and 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3, (abbreviated as BNT, BNT-25ST, BNT-35ST and BNST-BMH, respectively) ceramics were produced by solid state sintering method. The influence of solid solution of SrTiO3 and Bi(Mg0.5Hf0.5)O3 doping in Bi0.5Na0.5TiO3 on crystal structure, microstructure, electrical and energy storage performance were evaluated systematically. By optimizing ceramics composition, high breakdown field and slim hysteresis loops were simultaneously realized due to enhanced band gap, refined grain size and nano-domains formed, which can be verified by the transmission electron microscope (TEM), piezoelectric force microscope (PFM) and ultraviolet–visible spectrum. Therefore, an ultrahigh recoverable energy density of 5.59 J/cm3 with brilliant efficiency of 85.3% is realized in BNST-BMH ceramic. Besides, the BNST-BMH also exhibits prominent temperature stability at 20–140 °C, superior fatigue resistance beyond 105 cycles and outstanding frequency stability at 1–200 Hz. Our work offers a novel way for designing dielectric capacitors and also proves that BNST-BMH is indeed a great hopeful dielectric energy storage material in pulse power electronics.

Wake-up and fatigue mechanisms in ferroelectric Hf0.5Zr0.5O2 films with symmetric RuO2 electrodes

The mechanisms leading to wake-up and fatigue in ferroelectric hafnium zirconium oxide thin film devices with symmetric RuO2 electrodes are investigated via polarization, relative permittivity, dielectric nonlinearity, pyroelectric coefficient, and microfocus x-ray diffraction (XRD) measurements. The devices are observed to wake-up for up to 103 bipolar pulsed field cycles, after which fatigue occurs with polarization approaching zero following 108 cycles. Wake-up is accompanied by a decrease in both high-field permittivity and hysteresis loop pinching and an increase in the pyroelectric coefficient, indicating that the wake-up process involves a combination of transformations from the tetragonal to the orthorhombic phase and domain depinning from defect redistribution. Fatigue is observed to coincide with an increase in irreversible domain wall motion and a decrease in pyroelectric coefficient. Finite pyroelectric coefficients are measured on fully fatigued devices, indicating that domain pinning is a strong contributor to fatigue and that fatigued devices contain domain structures that are unable to switch under the fields applied for measurement. Microfocus XRD patterns measured on each device reveal that the phase constitution is qualitatively unaffected by field cycling and resultant polarization fatigue. These data indicate that the wake-up process has contributions from both phase transformations and domain depinning, whereas the fatigue process is driven primarily by domain pinning, and the near-zero measured switchable polarization is actually a poled device with immobile domains. These observations provide insight into the physical changes occurring during field cycling of HfO2-based ferroelectrics while examining a possible oxide electrode material for silicon CMOS device implementation.

Post-Depositional Fluid Flow in Jurassic Sandstones of the Uncompahgre Uplift: Insights From Magnetic Fabrics

The anisotropy of magnetic susceptibility (AMS) in sedimentary rocks results from depositional, diagenetic, syn- and post-sedimentary processes that affect magnetic grains. Some studies have also shown the potential role played by post-depositional fluid flow in detrital and carbonate formations. Here we present a new case study of Middle-Upper Jurassic sandstones where secondary iron oxides, precipitated from fluids that migrated through pores, give rise to the AMS. These sandstones are well exposed in the Uncompahgre Uplift region of the Central Colorado Trough, Colorado. The magnetic foliation of these undeformed, subhorizontal strata consistently strike NE-SW over a large distance with an average 45° dip to the SE. This steep AMS fabric is oblique with respect to the regional subhorizontal bedding and therefore does not reflect the primary sedimentary fabric. Also, outcrop-scale and microscopic observations show a lack of post-depositional plastic (undulose extinction) or pressure-solution (stylolites) deformation microstructures in these sandstones, hence precluding a tectonic origin. The combination of magnetic hysteresis, isothermal remanent magnetization, and thermal demagnetization of the natural remanent magnetization indicate that these rocks carry a chemical remanent magnetization born primarily by hematite and goethite. High-field magnetic hysteresis and electron microscopy indicate that detrital magnetite and authigenic hematite are the main contributors to the AMS. These results show that post-depositional iron remobilization through these porous sandstones took place due to the action of percolating fluids which may have started as early as Late Cretaceous along with the Uncompahgre Uplift. The AMS fabric of porous sandstones does not systematically represent depositional or deformation processes, and caution is urged in the interpretation of magnetic fabrics in these types of reservoir rock. Conversely, understanding these fabrics may advance our knowledge of fluid flow in porous sandstones and may have applications in hydrocarbon exploration.

Cobalt doping to influence the electrical conductivity of (Bi0.91Dy0.09)FeO3 ceramics

Rare earth modified bismuth ferrites are of interest as lead-free multiferroics, however reliable methods for reducing the electrical conductivity are needed. In this study ceramics with composition (Bi0.91Dy0.09)FeO3 were doped with 0.2 mol% cobalt (Co) and the impedance spectra, high electric field hysteresis and leakage current were compared to undoped ceramics. In pristine ceramics Co addition increased the bulk conductivity of the material but removed a relaxation from the dielectric loss and modulus in the frequency range 100 Hz–1 MHz. The remanent polarization and peak-to-peak strain of both ceramics were 38 µC/cm2 and 0.15% respectively, but surprisingly Co doped ceramics exhibited lower electrical leakage at above-coercive fields. Significant changes in the loss, modulus and leakage current of undoped ceramics after poling suggested that de-trapped charge carriers play a dominant role in the conductivity of undoped ceramics after poling. This effect was reduced by Co doping.

High-Frequency and High-Field Hysteresis Loop Tracer for Magnetic Nanoparticle Characterization

Existing metrology tools for magnetic nanoparticles cannot generate magnetic fields of the necessary high strength at high frequency to determine particle saturation and coercivity at conditions representative of their use, for example, in composite inductor cores, medical imaging, and hyperthermia treatments for cancer. To address this measurement need, this letter presents the design of a high-field and high-frequency hysteresis loop tracer capable of 0.16 T at 46.4 kHz. Hysteresis loops of commercial and custom iron oxide nanoparticles in varying sizes are measured and compared to typical vibrating sample magnetometer results in demonstration of the insight into nanoparticle behavior enabled by the new capabilities.

Magnetostatic interaction in soft magnetic bilayer ribbons unambiguously identified by first-order reversal curve analysis

Monolithic amorphous Fe73.5Nb3Si13.5B9Cu1/Fe74.5Nb3Si13.5B9 bilayer ribbons were obtained by double-nozzle melt-spinning and subsequently annealed to produce a composite with a tailored nano/micro-crystalline structure. The overall magnetic behavior is characterized by butterfly-shaped high field hysteresis loops and positively biased low field ones. The main questions we wish to address here are whether the global magnetic behavior of the bilayer can be separated into the individual contributions of each layer and the magneto-coupling between them can be well understood. For that purpose, we performed first-order reversal curve analysis, which enabled us to distinctly identify two phases, of ultra-soft and semi-soft magnetic natures, whose mutual predominant interaction is the magnetostatic coupling.

Reduction of Dielectric Hysteresis in Multilayered Films via Nanoconfinement

Micro/nanolayer coextrusion was used to fabricate polycarbonate (PC)/poly(vinylidene fluoride) (PVDF) layered films with significantly reduced dielectric losses while maintaining high energy density. The high-field polarization hysteresis was characterized for layered films as a function of PVDF layer thickness (6000 to 10 nm) and composition (10 to 70 vol % PVDF), and was found to decrease with decreasing layer thickness and PVDF content. To gain a mechanistic understanding of the layer thickness (or nanoconfinement) effect, wide-angle X-ray diffraction, polarized Fourier transform infrared spectroscopy, and broadband dielectric spectroscopy were employed. The results revealed that charge migration, instead of dipole flipping, was responsible for the hysteresis in multilayered films. The absence of PVDF dipole-flipping was attributed to the nonuniform electric field distribution in the layered structure, where the field in PVDF layers were calculated to be significantly lower than that in PC layers due t...

Effect of Ru-Doping on Magnetocaloric Effect in Pr Based Charge Ordered Manganites

It is shown that charge-orbital ordered antiferromagnetic state of the parent compound (x = 0) in Pr0.5Ca0.5Mn1-xRuxO3 series is destabilized and ferromagnetism is induced by Ru doping, as small as 3%, at the Mn site. The ferromagnetic transition temperature (TC) increases with Ru content from TC = 213 K for x = 0.03 to 239 K for x = 0.1 but the field dependence of magnetization does not show metamagnetic transition above or below TC unlike Pr0.5Ca0.5Mn1-xRuxO3. The change in magnetic entropy (?SM) is the largest for x = 0.03 (?SM = -4.2 J/kg K at 213 K for ?H = 5 T) and decreases with increasing Ru content (?SM = -3.8 J/kg K at 221K and -3.4 J/kg K at 239 K for ?H = 5 T, for x = 0.05 and 0.10, respectively). However, the relative cooling power increases with Ru content from 284.9 J/kg for x = 0.03 to 303.6 J/kg for x = 0.1. The large magnetic entropy change found in x = 0.03 and the absence of high field hysteresis in M-H curves make the Ru-doped samples suitable candidates for magnetic refrigeration.

Geomagnetic paleointensity dating of South China Sea sediments for the last 130 kyr

Relative paleointensity records from the northern South China Sea, northwest Pacific Ocean were studied in two gravity piston cores. Continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples. Detailed rock magnetic parameters, such as thermomagnetic and high-field hysteresis data, indicate that pseudo-single domain magnetite in a narrow range of grain-size and concentration is the main contributor to the remanent magnetization. The uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records. The relative paleointensity (RPI) curves were constructed by normalizing the natural remanent magnetization (NRM) with isothermal remanent magnetization (IRM), both in the 20–60 mT demagnetization state. Dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores. Furthermore, we have correlated our paleointensity records with NAPIS-75, S.Atlantic-1089, Sint-200 and NOPAPIS-250 to determine the chronological RPI framework for the South China Sea (SCS-PIS). Although some temporal offsets of paleointensity features between the different records have been recognized, their similar shape suggests that relative paleointensity on the 10 3–10 4 year scale is globally coherent and can provide an age framework for sediments independent of δ 18O ages.

Magnetic and electric transport properties of polycrystalline manganite Pr 0.6Na 0.4MnO 3

The magnetic and electric transport properties of the polycrystalline manganite Pr 0.6Na 0.4MnO 3 were reported. In zero field, the sample shows an insulator behavior. Under applied fields higher than 10 kOe, a field-induced insulator–metal transition occurs, and at the same time the colossal magnetoresistance (CMR) effect is also observed. At the temperature of 5 K, the metamagnetic transition from charge ordering/antiferromagnetic (CO/AFM) to ferromagnetic (FM) state is observed. With increasing temperature, the metastable FM phases can transform back to the CO state, accompanied by a high field hysteresis. The CMR effect of the sample can be understood by a percolative regime and is related to the CO–FM transition under a large magnetic field.

Magnetic and magneotransport properties of Nd 0.75Na 0.25MnO 3 manganite

We report the magnetic and magnetotransport properties of the polycrystalline manganite Nd 0.75Na 0.25MnO 3. In zero field, the sample shows a ferromagnetic insulator behavior. Under applied fields higher than 30 kOe, a field-induced insulator-metal, followed by a metal-insulator transition at a lower temperature occur; at the same time the colossal magnetoresistance (CMR) effect is also observed. At the temperature of 5 K, the metamagnetic transition from charge ordering/antiferromagnetic (CO/AFM) to ferromagnetic (FM) state is observed. With increasing temperature, the metastable FM phase can transform back to the CO state, accompanied by a high field hysteresis. The CMR effect of the sample can be understood by a percolative regime and is related to the CO-FM transition under a large magnetic field.

Structural and magnetic properties of zinc- and aluminum-substituted cobalt ferrite prepared by co-precipitation method

Spinal ferrites having the general formula Co1 − xZnxFe2 − xAlxO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were prepared using the wet chemical co-operation technique. The samples were annealed at 800°C for 12 h and were studied by means of X-ray diffraction, magnetization and low field AC susceptibility measurements. The X-ray analysis showed that all the samples had single-phase cubic spinel structure. The variation of lattice constant with Zn and Al concentration deviates from Vegard’s law. The saturation magnetization σs and magneton number nB measured at 300 K using high field hysteresis loop technique decreases with increasing x, suggesting decrease in ferrimagnetic behaviour. Curie temperature TC deduced from AC susceptibility data decreases with x, suggesting a decrease in ferrimagnetic behaviour.

Flux line motion in superconducting(YBa2Cu3O7−d)1−x/(SiO2)x composite systems in high magnetic fields

Superconducting (YBa2Cu3O7−d)1−x/(SiO2)x (i.e.Y123/S) composites with x = 0, 0.05, 0.1, 0.15 and 0.2 were prepared by solid state synthesis. Detailed investigations ofstructural and electrical transport and magnetization in applied magnetic fields(B = 0–9 T) were carried out. The typical double-step superconducting transitions observed both resistively(B = 0) andmagnetically (B = 1 mT) reveal the granular nature of all the samples. The XRD,SEM and superconducting transitions show that addition ofSiO2 mainly influences the inter-grain regions of the samples, leaving the pure Y123 phase inintra-grain regions practically intact. This leads to an interesting behaviour ofM(T,B) andresistivity ρ(T,B) in the samples. The field-cooled (FC) magnetizationM(T) measuredat B = 1 mT shows a dip in the diamagnetic transition at a characteristic temperaturethat coincides with the onset of the second step in the zero-field-cooled (ZFC)M(T) measured in the same field. In the presence ofB≥1 T, the broadening of the superconducting transition revealed byρ(T) below the first step is found to be field-dependent, whereas below the secondstep at lower temperatures the broadening becomes field-independent. The width(ΔM) of the high fieldhysteresis loops (M–B) measured isothermally in the superconducting state initially varies as a power law ofB. Dependingon SiO2 content and temperature, the power law further deviates into either a shallow peak or amonotonically decreasing curve. We show that these results and a host of otherconsiderations point towards an interaction of vortices in inter- and intra-grain regions.

Superconductivity in Pb inverse opal

Type-II superconducting behavior was observed in highly periodic three-dimensional lead inverse opal prepared by infiltration of melted Pb in blue ( D = 160 nm), green ( D = 220 nm) and red ( D = 300 nm) opals and followed by the extraction of the SiO 2 spheres by chemical etching. The onset of a broad phase transition (Δ T = 0.3 K) was shifted from T c = 7.196 K for bulk Pb to T c = 7.325 K. The upper critical field H c2 (3150 Oe) measured from high-field hysteresis loops exceeds the critical field for bulk lead (803 Oe) fourfold. Two well resolved peaks observed in the hysteresis loops were ascribed to flux penetration into the cylindrical void space that can be found in inverse opal structure and into the periodic structure of Pb nanoparticles. The red inverse opal shows pronounced oscillations of magnetic moment in the mixed state at low temperatures, T < 5.5 K. The shape of these oscillations and their temperature dependence indicate on phase transitions in the fluxoid state of Pb core. The weak matching effect in the field dependence of magneto-resistivity measurement at low magnetic fields and T > 0.9 T c has been observed for all of the samples studied. The magnetic field periodicity of resistivity modulation is in good agreement with the lattice parameter of the inverse opal structure. We attribute the failure to observe pronounced modulation in magneto-resistive measurement to difficulties in the precision orientation of the sample along the magnetic field.

Environmental magnetic studies on some Quaternary sediments of varied depositional settings in the Indian sub-continent

The efficacy and limitations of routine environmental magnetic approaches to characterize and compare the Quaternary sediments of varied depositional settings (fluvial, fluvio-lacustrine and marine) from the Indian sub-continent are discussed. The various studied profiles fall under tropical wet and dry, subtropical humid, cold arid and alpine climatic zones at altitudes varying from ∼2000 m below sea level to ∼4500 msl. The magnetic mineral assemblages are characterized by magnetic susceptibility, high field hysteresis parameters and their ratios and bivariate plots. Besides applying the conventional models, we produced new and multi-parametric environmental magnetic models for finer discrimination of the mineral magnetic assemblages (MMA) amongst these deposits. In similar hinterland setup and climate zones, independent MMA characteristics are shown by the Late Quaternary frontal Himalayan basins: the Ganga basin, the intermontane Pinjor Dun and the folded Siwalik sequence. Such variations are attributed to diverse energy conditions due to varied basin morphology, climate and the source to sink proximity. Contrasting channel to overbank MMA relations are discernible during the glacial and interglacial periods within the Ganga Basin. The Siwalik sediments are notably restricted to antiferromagnetic region of the bivariate plots indicating formation and stability of iron oxides under warm humid to arid conditions. The post-Siwalik intermontane sediments show steep gradients in MMA domain within a short distance from proximal to distal fan regime. In the tropical Peninsular region, the ‘source to sink’ relation is marked by the Deccan Trap province (source) and Bengal submarine fan (sink) at least since the Last Glacial Maxima (LGM) in the Middle fan region. The MMAs for the lacustrine and fluvio-lacustrine deposits in the Himalayan foothills as well as the Higher Himalaya indicate detrital variations governed by the fluvial dynamics in the region. This demands a more detail catchment to sink studies in each basin and to explore the climatic tele-connections amongst the varied altitudinal regions. Overall, this study indicates a strong detrital control on MMA governed by the energy conditions of the transporting media that in turn is controlled by catchment morphology, regional tectonics and climatic fluctuations. In the absence of suitable unmixing models, the new bivariate and diamond plots attempted here are helpful in describing the detrital modes within the basin and its comparison to other basins.

Variations of the geomagnetic field during the Holocene: Relative paleointensity and inclination record from the West Pacific (ODP Hole 1202B)

We conducted detailed rock magnetic investigations on 36 m of drill core collected during Ocean Drilling Program Leg 195 at Hole 1202B (24°48.24′N, 122°30.00′E), in the Southern Okinawa Trough, with the goal of extracting a reliable paleointensity signal with centennial resolution. An age-depth model was established from a chronology obtained by accelerator mass spectromety 14C dating. The sedimentary section spans almost the entire Holocene (0–9.4 kyr) and exhibits sedimentation rates close to 400 cm/kyr. The magnetic properties are dominated by stable, pseudo-single domain magnetite. High-field hysteresis data and the grain-size sensitive ratio of anhysteretic remanent magnetization (ARM) to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations. Magnetic parameters vary by a factor of 4 thereby fulfilling the usual criteria for a relative paleointensity study. The relative geomagnetic paleointensity was obtained by normalizing the intensity of natural remanent magnetization (NRM) by the ARM and the low field magnetic susceptibility. Both normalizations yield nearly identical results ( r = 0.89). Spectral analysis indicates that the record is not significantly affected by local environmental conditions. Comparison of this West Pacific paleointensity curve with other curves suggests a geomagnetic origin for the signal. Millennial-scale features of our record correlate to variations of the archeomagnetic dipole moment. This suggest that the sediments at Hole1202B recorded changes of the geomagnetic field over the studied time interval.

Reversible hysteresis loop tuning

We utilize antiferromagnetically coupled bilayer structures to magnetically tune hysteresis loop properties. Key element of this approach is the non-overlapping switching field distribution of the two magnetic layers that make up the system: a hard magnetic CoPtCrB layer (HL) and a soft magnetic CoCr layer (SL). Both layers are coupled antiferromagnetically through an only 0.6-nm-thick Ru interlayer. The non-overlapping switching field distribution allows the measurement of magnetization reversal in the SL at low fields while keeping the magnetization state of the HL unperturbed. Applying an appropriate high field or high field sequence changes the magnetic state of the HL, which then influences the SL magnetization reversal due to the interlayer coupling. In this way, the position and shape of the SL hysteresis loop can be changed or tuned in a fully reversible and highly effective manner. Here, we study specifically how the SL hysteresis loop characteristics change as we move the HL through an entire high field hysteresis loop sequence.