Magnetization Jumps Research Articles

Correlation Between the Crystal Structure and Magnetic Properties of Bi1−yCayFe1−xMnxO3 Multiferroics near the Polar-Anti(non)polar Phase Boundary

This paper reports the results of a systematic investigation into the magnetic properties of Bi1−yCayFe1−xMnxO3 (0.1 ≤ y ≤ 0.175, 0.35 ≤ x ≤ 0.45) solid solutions. The substitution of Bi3+ with Ca2+ and the concurrent introduction of Mn3+/Mn4+ ions result in the stabilization of various structural phases, with each exhibiting distinct magnetic characteristics. The investigation indicates that the samples containing the polar rhombohedral phase display metamagnetic transitions at low temperatures, characterized by pronounced jumps in magnetization. Single-phase samples with a nonpolar orthorhombic structure exhibit weak ferromagnetic behavior without metamagnetic features. The observed metamagnetic behavior, accompanied by anomalies in temperature-dependent magnetization and significant remnant magnetization at low temperatures, particularly in samples near the polar-anti(non)polar phase boundary, highlighted the presence of both antiferromagnetic and glassy magnetic components.

Barkhausen Noise as A Magnetic Nondestructive Testing Technique

Magnetic Barkhausen Noise (MBN) is a magnetic-based non-destructive electromagnetic testing method. Due to the electromagnetic working principle of MBN, it can be used for ferromagnetic materials, which consist of small magnetic fields discredited by domain walls and oriented in various directions. In an external magnetic field application, the fields turn to the magnetic direction, and the domain walls move and cause magnetic flux jumps. The jumps are named Barkhausen Noise (BN). The domain wall movements are sometimes pushed down by microstructure, composition, and defects. As the magnetic domain walls break away from the pinning sites produce MBN signal. MBN can be used for different material properties such as microstructure, composition, residual stress, and hardness. The paper's purpose is to analyze MBN as an improved NDT, clarify the relationship between material properties and MBN profile, and introduce MBN's applications and test equipment of MBN.

Electromechanical behavior of a rectangular bulk superconductor with an inhomogeneous critical current density under pulsed-field magnetization

Bulk high-temperature superconductors are widely used in various superconducting devices for their high critical current density and the ability to trap large magnetic field. In some applications, bulk superconductors can be arranged in an array structure to increase the magnetic field strength. However, rectangular bulk superconductors can be arranged more compactly than commonly used cylindrical bulk superconductors. The unique shape of rectangular bulk superconductors results in different distributions of electromagnetic fields, temperature, and stress under a pulsed-field magnetization (PFM) than for cylindrical bulk superconductors. In bulk superconductors, growth sector boundaries and growth sector regions have different critical current density, resulting in an uneven critical current density. Therefore, in this study, the electromagnetic and mechanical behavior of non-uniform rectangular bulk superconductors during the PFM process is investigated. The corresponding distribution and variation in the magnetic field, current, temperature, and stress in the bulk are calculated and analyzed. The influence of rectangle aspect ratio on the electromagnetic and mechanical behavior is discussed. The calculation results show that the magnetic flux jumps occur accompanied by sudden changes in the temperature and pressure. The effect of the aspect ratio of rectangular bulk superconductors on their electromagnetic and mechanical properties is analyzed. The influence of preexisting cracks in a non-uniform rectangular bulk superconductor on the simulation results is discussed. The numerical results indicate that the presence of an edge crack exacerbates the magnetic flux jump as well as the jumps in the temperature and stress. However, a central crack has a relatively small effect on the stability of a bulk superconductor.

Magnetic properties of ferro-antiferromagnetic spin triangle chain

Frustrated spin- 12 model consisting of a linear chain of triangles with ferro (F)- and antiferromagnetic interactions connected by ferromagnetic interactions (triangles chain) is studied. The ground state phase diagram depending on the interaction ratios consists of ferromagnetic, two ferrimagnetic and singlet phases. The magnetic properties in these phases are analyzed both analytically and numerically. We show that in some regions of the singlet phase the magnetization curves have magnetization plateau and magnetization jumps. We study the thermodynamics and its relation to the specific structure of the excitation spectrum of the triangle chain.

Anomalous Magnetic Viscosity in (Sm,Zr)Fe<sub>11</sub>Ti Alloys with ThMn<sub>12</sub>-Type Structure

Abstract—Magnetic properties of the microcrystalline Sm1 – xZrxFe11Ti (x = 0, 0.1, 0.2) alloys with ThMn12-type structure were investigated. Irreversible jumps of magnetization on major hysteresis loops at low temperatures (2–4 K) were found. The jumps are random either in the magnitude of the magnetic field in which they occur or in their amplitude, and are independent of the chemical composition. There is a specific annealing temperature for each alloy, above which magnetization jumps are not observed in annealed alloys at low temperatures. The magnetic viscosity of Sm0.9Zr0.1Fe11Ti alloy annealed at 700°C was investigated at temperatures of 2–4 K. The magnetic viscosity coefficient has a discontinuity in the field of magnetization jump. This behavior is explained by thermal processes occurring during magnetization of the alloy through the magnetization jump.

Hybrid Superconducting/Superconducting Mesoscopic Heterostructure Studied by Modified Ginzburg–Landau Equations

Studies involving vortexes in hybrid superconducting devices and their interactions with different components inside samples are important for reaching higher values of critical parameters in superconducting materials. The vortex distribution on each side of a sample with different fundamental parameters, such as temperature T, penetration depth λ, coherence length ξ, electron mass m, and the order parameter Ψ, may help to improve the superconducting properties. Thus, in this work, we used the modified Ginzburg–Landau theory to investigate a hybrid superconductor (HS), as well as to provide a highly tunable and adjustable theoretical tool for theoretically explaining the experimental results involving the HS in order to study the vortex behavior in superconductors of mesoscopic dimensions with extreme differences among their fundamental parameters. Therefore, we evaluated the influence of the HS on the vortex configuration and its effects on field-dependent magnetization. The results show that when the applied magnetic field H was increased, the diamagnetic response of the HS (Meissner effect) included additional jumps in magnetization, while diamagnetism continued to increase in the sample. In addition, the differences among parameters created an interface between both components, and two different magnitudes of supercurrent and vortex sizes caused less degradation of the local superconductivity, which increased the upper critical field. On the other hand, this type of HS with differences in parameters on both sides can be used to control the vortex movement in the selected sample of the superconducting region with more accuracy.

Thermomagnetic instabilities in 3D network of superconducting lead nanofilaments in porous glass

Thermomagnetic instabilities in the lead-porous glass (Pb-PG) nanocomposite in superconducting state were studied, and a model was proposed that relates magnetization jumps and heat release spikes with average critical current density. The samples were created by filling porous glass (characteristic pore size d = 7 nm) with lead from a melt under pressure, which created a 3D multiply connected system of lead filaments. The critical temperature of superconducting transition in Pb-PG T c = 7.2 K is the same as for bulk lead and the critical magnetic field H c (0) ≈ 40 kOe is much higher than H c bulk (0) ≈ 800 Oe for bulk lead. Hysteresis and magnetic flux jumps were observed in the magnetization curves m(H) of the Pb-PG nanocomposite, which are connected with the formation of magnetic flux gradients in a system of interconnected contours. Magnetic flux jumps are thermomagnetic processes accompanied by heat release which was directly observed by measuring adiabatic temperature change in the sample during magnetic field sweep. The flux jumps in the magnetization and heat release events were almost periodic in the magnetic field. The period dependences on the magnetic field are similar to the calculated average critical current density dependence j c (H).

Magneto-optical measurements of mesoscopic Nb superconducting structures using a ferromagnetic metal indicator layer

Imaging local magnetic fields produced by nano- and micrometer-scale superconductors has become a vital tool that can not only reveal crucial information on the vortex dynamics and order parameters of the superconducting materials but also visualize the working mechanism of superconducting devices made for quantum information. Here, we performed measurements of the magnetic field distributions of mesoscopic superconducting structures with various geometries by combining a thin ferromagnetic metal layer as a magneto-optical sensing element that responds to the environmental magnetic fields and a custom-made sensitive Sagnac interferometer. The sensitivity of the technique enables the observation of magnetic flux jumps due to individual vortex entries into nanostructured superconductors. In addition, with the control of incident power at a focused laser spot, we induce thermally driven movement of vortices that leaves a trace of a microscopic optical heating pattern.

Giant magnetization jumps in multiscale-distortion dual-antiferromagnetic system

Large magnetization jumps (MJs) can realize an avalanched flip of the spin structure from a low spin state (antiferromagnetic) to a high spin state (ferromagnetic) and has potential applications in spin devices. Here, we report giant MJs in dual-antiferromagnetic hematite-ilmenite (Fe2O3)0.1(FeTiO3)0.9 (HI-9) solid solution. The obtained intensity of MJs (the ratio of an abrupt change in magnetization to saturation magnetization) increases to 53.3%, which is about twice as much as previously reported values in HI-9. These unusually large MJs are achieved by intentionally introducing multiscale distortions with high-stress compression deformation. Both experiments and Monte Carlo simulations demonstrate that the increase in MJs' intensity originates from the tunable atomic-scale and nano-scale distortions induced by crystal strain energy during the deformation process. Our findings provide an approach to modulate metamagnetic transitions and may inspire fresh ideas for creating high-performance antiferromagnetic materials.

Magnetic Instabilities in the Quasi-One-Dimensional K2Cr3As3 Material with Twisted Triangular Tubes.

The magnetic response of a frustrated K2Cr3As3 sample having triangular arrays of twisted tubes has been studied by means of dc magnetization measurements as a function of the magnetic field (H) at different temperatures ranging from 5 K up to 300 K. Looking at the magnetic hysteresis loops m(H), a diamagnetic behavior of the sample was inferred at temperatures higher than 60 K, whereas at lower temperatures the sample showed a hysteresis loop compatible with the presence of ferrimagnetism. Moreover, spike-like magnetization jumps, both positive and negative, were observed in a narrow range of the magnetic field around 800 Oe, regardless of the temperature considered and they were compared with the theoretical predictions on frustrated systems. The field position of the magnetization jumps was studied at different temperatures, and their distribution can be described by a Lorentzian curve. The analogies between the expected features and the experimental observations suggest that the jumps could be attributed to the magnetic frustration arising from the twisted triangular tubes present in the crystal lattice of this compound.

Majorana Anyon Composites in Magneto-Photoluminescence Spectra of Natural Quantum Hall Puddles.

In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius rs~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling factors ν > 1 (B < 10 T). Additionally, we observed B-hysteresis of the jumps and a dependence of all these anomalous features on rs. Using a theoretical description of the magneto-PL spectra and an analysis of the electronic structure of these dots based on the single-particle Fock–Darwin spectrum and many-particle configuration-interaction calculations, we show that these observations can be described by the rs-dependent formation of the anyon (magneto-electron) composites (ACs) involving single-particle states having non-zero angular momentum and that the anyon states observed involve Majorana modes (MMs), including zero-B modes having an equal number of vortexes and anti-vortexes, which can be considered as Majorana anyons. We show that the paramagnetic shift corresponds to a destruction of the equilibrium self-formed ν~5/2 AC by the external magnetic field and that the jumps and their hysteresis can be described in terms of Majorana qubit states controlled by B and rs. Our results show a critical role of quantum confinement in the formation of magneto-electrons and implies the liquid-crystal nature of fractional quantum Hall effect states, the Majorana anyon origin of the states having even ν, i.e., composite fermions, which provide new opportunities for topological quantum computing.

A theoretical simulation for MBN testing: Modeling microscopic local magnetization jumps in magnetic domain movement

Magnetic Barkhausen Noise (MBN) signals are adoped for the non-destructive evaluation of residual stress and plastic deformation due to their sensitivity to micro defects in material. Such MBN signals originate from discontinuous magnetization jumps accompanied by blocking of the pinning effect on the magnetic domain. This paper analyzes the influencing factors and laws of MBN non-destructive evaluation by numerically simulating discontinuous magnetization jumps. The pinning effect on the movement of the magnetic domain is considered as a random barrier field with a Gaussian distribution, and the discontinuous magnetization jumps are described as a transition in the local magnetization state. Solving Maxwell equations under varying current excitations based on the finite difference method allows simulating the magnetization evolution during non-destructive testing based on an iterative algorithm to realize MBN signal analysis. The theoretical analyses combined with existing experimental data show that the simulations can predict the influence of the excitation frequency, plastic deformation and stress level on the MBN signals, while also give explanations on some basic experimental phenomena and laws. This proposed theoretical simulation method is available to describe the mechanisms and causes of the MBN signals from a microscopic perspective for magnetic jump events.

Anomalous magnetization jumps in granular Pb superconducting films

In granular superconductors, the grain boundaries are closely related to the vortex dynamics and the macroscopic superconducting properties. In our research, Pb films with different grain sizes were prepared by tuning the substrate temperature. With the grain size decreasing, Pb films are prone to feature the anomalous magnetization jumps in the M − T curves, while in the M − H curves flux avalanche happens. Both phenomena appear in the same region of the H − T phase diagram and thus are considered to have the same origin. The further theoretical analysis shows that with grain size decreasing the pinning mechanism evolves from a mixed δTc and δl pinning to the δl pinning mechanism. The results shed light on the study of pinning mechanism for granular superconductors and is beneficial to the potential application of manipulating vortex pinning by regulation of intrinsic defects.

Large magnetization jumps in Ca-doped bismuth ferromanganite

Magnetic properties of the phase-separated (antiferromagnetic + glassy) Bi0·85Ca0·15Fe0·6Mn0·4O3 multiferroic have been studied over a wide temperature range. It has been found that the material exhibits a metamagnetic transition (shifting toward smaller fields with decreasing temperature) which is accompanied by the magnetization jumps whose value (up to ∼4 emu/g at T = 2 K) far exceeds that characteristic of the field-driven transformation from the cycloidal to the canted antiferromagnetic order in the pure BiFeO3. The metamagnetic behavior can be explained as originating from the spin-reorientation transition in the long range-ordered antiferromagnetic phase and involving magnetic moments from the glassy-like phase. The obtained results shed new light on the conditions favoring the coexistence of large switchable magnetization and spontaneous electric polarization in BiFeO3-based multiferroics.

Colossal magneto-resistive relaxation effects in La0.9Ce0.1Fe12B6

The study of the magnetic, electronic transport, and magnetotransport properties of La0.9Ce0.1Fe12B6 itinerant-electron system has been performed by combining magnetization, electrical resistivity, and magnetoresistance experiments. Along with the antiferromagnetic (AFM) ordering at TN = 35 K, two consecutive magnetic transformations, antiferromagnetic–ferromagnetic (AFM–FM) and ferromagnetic–paramagnetic (FM–PM), occur upon heating under certain magnetic field values. At fixed temperatures, it is revealed that both AFM and PM phases can be converted into the FM phase irreversibly and reversibly via a first-order metamagnetic transition associated with a large hysteresis. Below 8 K, the metamagnetic transition is discontinuous, manifesting itself by multiple sudden jumps in magnetoresistance and magnetization. A giant negative magnetoresistance effect of about −78% is found. We further demonstrate that the time dependencies of the electrical resistivity and the magnetization exhibit colossal spontaneous steps after an incubation time in conditions where both the applied magnetic field and temperature are constant. Another intriguing observation in the phase diagram is the presence of a critical point at the crossover of the three distinct PM, FM, and AFM magnetic states.

Zero-field cooling exchange bias induced by spin metastable state in MnNiGa system

<p indent="0mm">The existence of the spin metastable state in magnetic materials often causes novel physics including magnetization jumps, metamagnetic transition, and skyrmions. In this paper, we design the occupancy of Mn atoms in the MnNiGa system, and based on first-principles calculations, we anticipate the existence of spin metastable state in Mn₂Ni_1.5Ga_0.5. Therefore, Mn₂Ni₂₋_{<italic>x</italic>}Ga_{<italic>x</italic>} (<italic>x</italic>=0.36–0.60) is selected as the research platform to carry out related research. The experimental results show that near the composition of Mn₂Ni_1.5Ga_0.5, the lattice constant, crystal axis ratio, DC and AC magnetic test all have abnormal changes, and the zero-field cooling exchange bias is observed, which indicates the dual effects of the spin metastable state on structure and magnetic structure, and proves the dominant effect of spin metastable state on zero-field cooling exchange bias. This work provides a new idea for the design of spin metastable states in magnetic materials, and a new method for the realization of a zero-field cold exchange bias system.

Enhanced magnetocaloric effect in a mixed spin-(1/2, 1) Ising–Heisenberg two-leg ladder with strong–rung interaction

The magnetic and magnetocaloric properties of the mixed spin-(1/2,1) Ising-Heisenberg model on a two-leg ladder with dimer-rung alternation are exactly examined under an adiabatic demagnetization process using the transfer-matrix formalism. We notify that the magnetization curve of the model exhibits plateaux as a function of the applied magnetic field and cyclic four-spin Ising interaction at certain rational fractions of the saturation value. We precisely investigate the ability of cooling/heating of the model nearby the critical points at which discontinuous ground-state phase transition occurs. It is evidenced that the model manifests an enhanced magnetocaloric effect in a proximity of the magnetization steps and jumps, accompanying with the plateaux and jumps of correlation function of the dimer spins. We conclude that not only the cooling/heating capability of the model could be pleasantly demonstrated by the applied magnetic field variations, but also a typical cyclic four-spin Ising interaction plays essential role to determine an efficiency of the magnetocaloric effect of the model.

Comparative study of the magnetic phase diagrams and spin-flop-driven magnetodielectric responses of the pure and Mn3+-doped Pb2Fe2Ge2O9 single crystals

The Pb2Fe2-xMnxGe2O9 (x = 0.43) orthorhombic antiferromagnet single crystals have been synthesized by a modified pseudo-flux technique and their magnetic and magnetodielectric properties have been investigated. It has been established that partial substitution of highly anisotropic Mn3+ ions for iron ones significantly affects the magnetic structure of the crystal. Under magnetization of the crystal along the rhombic b and c axes, magnetization jumps have been detected, which are indicative of the occurrence of orientational transitions identified as first-order ones. No weak ferromagnetism characteristic of the pure crystal in the rhombic a axis direction has been detected. The field dependences of the magnetization for the pure and Mn-doped crystals have been analyzed using the thermodynamic potential that takes into account the crystal symmetry. It has been shown that, in the Mn-substituted crystal, the antiferromagnetic vector in the ground state is parallel to the rhombic b axis; in this state, weak ferromagnetism has not been observed. Under magnetization along the b axis, a conventional spin-flop transition occurs. The orientational transition under magnetization along the c axis has been attributed to the reorientation of the antiferromagnetic vector relative to the a axis with the simultaneous occurrence of a weak ferromagnetic moment along the c axis. Magnetic phase diagrams of the Mn-doped crystal for the magnetic fields H||b and H||c have been built.In the Mn-doped crystal, at E||c and H||c, the orientational transition-induced magnetodielectric response jump has been detected, which is higher than the jumps observed for the undoped crystal by a factor of 3. The magnetodielectric properties of the pure and Mn-doped crystals have been analyzed using their magnetic phase diagrams.

Magnetic anomalies, chemical and magnetic properties at wide temperature range (15–1000 K) in LiSrxFe5-xO8 (x = 0, 0.025, 0.05)

We report on magnetic anomalies at low temperatures, high Curie temperature values, structural and chemical properties of Sr doped LiFe5O8 bulk material. Micron size LiSrxFe5−xO8 (x = 0, 0.025, 0.05) are seen to crystallize in ordered α-LiFe5O8 phase with the space group of P4332. Chemical states of Li, Fe, Sr and O are confirmed from X-ray photoelectron spectroscopy measurements. Domain wall thickness is calculated to be 60 nm, 59.4 nm and 52.5 nm for x = 0, 0.025, 0.05 samples respectively. Field cooled (FC) and zero field cooled (ZFC) measurements from 300 K to 15 K shows several anomalies in LiSrxFe5−xO8 (x = 0, 0.025, 0.05) samples. Magnetic anomalies are observed at Tm1 (275 K), Tm2 (225 K), Tm3 (125 K), Tm4 (80 K) and Tm5 (30 K) for the pure LiFe5O8 sample and for the Sr doped samples, two sharp jumps in magnetization are observed around Tm6 (250 K) and Tm7 (75 K). Saturation magnetization and Curie temperature values are seen to decrease with the partial substitution of Sr2+ ions for the Fe3+ ions in α-LiFe5O8 structure. Remanent magnetization, magnetocrystalline anisotropy constant (K1) and coercivity values are seen to increase with increasing Sr concentration. LiSrxFe5−xO8 (x = 0, 0.025, 0.05) samples exhibit magnetic anomalies at low temperatures and exhibit hard magnetic behavior with Sr substitution.

The Impact of Disorder on the Disappearance of Metamagnetic Behavior and Enhancement of Temperature Coefficient of Resistivity for (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 Ceramics

The polycrystalline samples (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 were prepared by the solid-state reaction method. Magnetization measurements versus temperature were performed in order to investigate the magnetic properties such as the metamagnetic transition. The transition temperature estimated from the maximum of dM/dH is found sensitive to disorder σ2 leading to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps. The peak temperature coefficient of the resistivity improved significantly from 1.54 to 8.21% K−1 due to the increase in disorder. These findings suggest that (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 ceramics can be used to prepare uncooled infrared bolometers.