Changes In Magnetic Properties Research Articles

Effect of Surface Oxidation and Crystal Thickness on the Magnetic Properties and Magnetic Domain Structures of Cr2Ge2Te6.

van der Waals (vdW) magnetic materials, such as Cr2Ge2Te6 (CGT), show promise for memory and logic applications. This is due to their broadly tunable magnetic properties and the presence of topological magnetic features such as skyrmionic bubbles. A systematic study of thickness and oxidation effects on magnetic domain structures is important for designing devices and vdW heterostructures for practical applications. Here, we investigate thickness effects on magnetic properties, magnetic domains, and bubbles in oxidation-controlled CGT crystals. We find that CGT exposed to ambient conditions for 5 days forms an oxide layer approximately 5 nm thick. This oxidation leads to a significant increase in the oxidation state of the Cr ions, indicating a change in local magnetic properties. This is supported by real-space magnetic texture imaging through Lorentz transmission electron microscopy. By comparing the thickness-dependent saturation field of oxidized and pristine crystals, we find that oxidation leads to a nonmagnetic surface layer that is thicker than the oxide layer alone. We also find that the stripe domain width and skyrmionic bubble size are strongly affected by the crystal thickness in pristine crystals. These findings underscore the impact of thickness and surface oxidation on the properties of CGT, such as saturation field and domain/skyrmionic bubble size, and suggest a pathway for manipulating magnetic properties through a controlled oxidation process.

Gas‐Induced Electrical and Magnetic Modulation of Two‐Dimensional Conductive Metal–Organic Framework

AbstractControlled modulation of electronic and magnetic properties in stimuli‐responsive materials provides valuable insights for the design of magnetoelectric or multiferroic devices. This paper demonstrates the modulation of electrical and magnetic properties of a semiconductive, paramagnetic metal−organic framework (MOF) Cu3(C6O6)2 with small gaseous molecules, NH3, H2S, and NO. This study merges chemiresistive and magnetic tests to reveal that the MOF undergoes simultaneous changes in electrical conductance and magnetization that are uniquely modulated by each gas. The features of response, including direction, magnitude, and kinetics, are modulated by the physicochemical properties of the gaseous molecules. This study advances the design of multifunctional materials capable of undergoing simultaneous changes in electrical and magnetic properties in response to chemical stimuli.

Gas-Induced Electrical and Magnetic Modulation of Two-Dimensional Conductive Metal-Organic Framework.

Controlled modulation of electronic and magnetic properties in stimuli-responsive materials provides valuable insights for the design of magnetoelectric or multiferroic devices. This paper demonstrates the modulation of electrical and magnetic properties of a semiconductive, paramagnetic metal-organic framework (MOF) Cu3(C6O6)2 with small gaseous molecules, NH3, H2S, and NO. This study merges chemiresistive and magnetic tests to reveal that the MOF undergoes simultaneous changes in electrical conductance and magnetization that are uniquely modulated by each gas. The features of response, including direction, magnitude, and kinetics, are modulated by the physicochemical properties of the gaseous molecules. This study advances the design of multifunctional materials capable of undergoing simultaneous changes in electrical and magnetic properties in response to chemical stimuli.

Effect of divalent ion of strontium substitution on the structural, optical, magnetic and blood compatibility studies in cobalt ferrite

This study investigates the effects of Sr2+ substitution on the structural, morphological, and magnetic properties of magnetic cobalt ferrite (CoFe2O4). Through sol–gel auto-combustion synthesis, Sr2+ was substituted into Co-spinel ferrites (Co1-xSrxFe2O4, where x = 0.0, 0.25, 0.5, 0.75, 1.0). SEM analysis revealed spherical grains with an average size of 54.4 nm. XRD analysis indicated systematic changes in crystallographic parameters and the formation of secondary phases with Sr-substitution. While the crystal size for CoFe2O4 was calculated as 262 nm, this value was determined as 18 nm for Co0.25Sr0.75Fe2O4. FT-IR results suggested increased force constants of octahedral and tetrahedral bonds with higher Sr content, with main vibration bands at 423.6 and 606 cm−1. M-H curves exhibited S-shaped behavior, indicating drastic magnetic property changes with Sr2+ substitution. Coercivity field (Hc), saturation magnetization (M S ), and remanent magnetization (M r ) values ranged from 1447.8–545.4 Oe, 58.8-14 emu g−1, and 36.8-7.6 emu g−1, respectively. Blood compatibility experiments highlighted Co0.75Sr0.25Fe2O4 nanoparticles with significantly low hemolysis rates compared to other concentrations.

Magnetic property changes of NdGa upon hydrogen absorption

Magnetic property changes of NdGa upon hydrogen absorption

Characterizing changes in microstructures, mechanical and magnetic properties of non-oriented silicon steel due to pulsed current

In this paper, the influence of electrical pulse treatment (EPT) on the evolution of microstructure and texture and the resultant magnetic and mechanical properties of a cold rolled Nb-alloyed non-oriented silicon steel (NOSS) was investigated carefully. When the temperature rise caused by Joule heat is higher than the starting temperature of dissolution, more precipitates are dissolved in the EPT specimens than those subjected to the conventional heat treatment (CHT) at the same temperature, and higher current density resulted in Laves precipitates dissolved at lower temperature. The permeability of all the EPT and CHT specimens increase first and then decrease with the increasing temperature, and it reaches the maximum at the temperature for nearly the complete recrystallization. B50 is higher for the EPT specimen than CHT before the completion of recrystallization due to enhanced recrystallization, but lower than CHT after the completion because the athermal effect of pulsed current promotes the growth of γ-fiber grains, disfavoring the permeability. Moreover, the EPT specimen has the lower iron loss and lower yield strength than the CHT one at the same annealing temperature, because the dissolution of precipitates, recrystallization and grain growth in cold rolled matrix are all enhanced due to the athermal effect of pulsed current.

Tuning the coercivity of synthetic antiferromagnetic nanoplatelets with perpendicular anisotropy by varying the Co1−xBx alloy composition

Synthetic antiferromagnetic (SAF) nanoplatelets (NPs) with perpendicular magnetic anisotropy based on archetype SAF structures, e.g., Pt/Co/Ru/Co/Pt are of particular interest for torque-related bio-applications due to their large uniaxial magnetic anisotropy. However, when the diameter of the NPs is reduced, the magnetic properties change. For instance, the coercive field increases and starts to vary strongly from NP to NP in a batch due to an increased variation in the reversal probability dominated by local defects. In this study, we investigate how the concentration of boron (B) in Co1−xBx affects the switching properties of NPs, because the addition of B renders the Co layer amorphous and hence introduces more defects. Moreover, it reduces variations in local crystalline anisotropy making the magnetic properties of the NPs more soft. Specifically, we show that the coercivity of the NPs decreases with higher B concentration. This decrease is explained by two mechanisms: (i) the loss of interfacial anisotropy due to less Co–Pt hybridization at the Pt–Co interface and (ii) an increase in the surface’s magnetic domain nucleation site density leading to a narrower distribution of the coercivity of an ensemble of NPs. This understanding will greatly help the field of NP-torque related applications as the spread in applied torque from the NPs to their surroundings can be homogenized.

Bending strain–induced changes in perpendicular magnetic properties of Pt/Co/Pt films on flexible substrates

We studied the irreversible changes in the perpendicular magnetic properties of Pt(2.2 nm)/Co(0.8 nm)/Pt(2.2 nm) films deposited on a flexible polyethylene terephthalate substrate with bending deformation. The changes in the magnetic properties of the Pt/Co/Pt film with deformation were analyzed using magneto-optical Kerr-effect microscopy. The film was bent in one direction using cylindrical rods or semicylindrical grooves of different radii and then restored to the initial flat state. No significant changes in the magnetic properties due to bending strain were observed below a critical bending curvature. However, for bending curvatures above +0.25 mm−1 or below −0.14 mm−1, the magnetic domain shape changed from circular to elongated ellipses, perpendicular to the bending direction, and the coercivity of the film increased by 10%–30%. Furthermore, the domain wall motion exhibited a distinct anisotropic behavior, with ∼12-fold difference in the velocity of domain wall motion in different directions. Conclusively, the magnetic properties of the Pt/Co/Pt film fabricated on a flexible substrate exhibited irreversible changes beyond a critical deformation of +2.44% or −1.37%.

Eu Doping in the GdCd7.88 Quasicrystal and Its Approximant Crystal GdCd6.

The effect of Eu doping in the Tsai quasicrystal (QC) GdCd7.88 and its periodic 1/1 approximant crystal (AC) GdCd6 are investigated. This represents the first synthesis of Eu-containing stable QC samples, where three samples with the final composition Gd1-xEuxCd7.6±α at Eu doping concentrations x = 0.06, 0.13, and 0.19 are obtained (α ∼ 0.2). They are compared to two 1/1 ACs with compositions Gd1-xEuxCd6 (x = 0.12, 0.16). In addition, a new type of 1/1 AC, differing only by the inclusion of extra Cd sites unique to the Eu4Cd25 1/1 AC, has been discovered and synthesized for the concentrations Gd1-xEuxCd6+δ (x = 0.25, 0.33, 0.45, 0.69, 0.73, and 0 < δ ≤ 0.085). Due to the preferred cube morphology of its single grains, we refer to them as c-type 1/1 ACs and to the conventional standard ones as s-type. In both QCs and s-type ACs, the Eu content appears to saturate at a concentration of ∼20%. On the other hand, any Gd| Eu ratio is allowed in the c-type ACs, varying continuously between GdCd6 and Eu4Cd25. We describe and contrast the changes in composition, atomic structure, specific heat, and magnetic properties induced by Eu doping in the quasicrystalline phase and the s-type and c-type 1/1 ACs. By comparing our results to the literature data, we propose that the occupancy of the extra Cd sites can be used to predict the stability of Tsai-type quasicrystalline phases.

Acoustic shock wave processing on amorphous carbon quantum dots – correlation between spectroscopic-morphological–magnetic and electrical conductivity properties

In this context, we report the acoustic shock wave processing on amorphous Carbon quantum dots (a-CQD) such that its degree of graphitization and magnetic properties are analyzed. Analytical techniques such as the Raman spectrometer, high resonation–transmission electron microscopy (HR-TEM) and vibrating sample magnetometer (VSM) are utilized to understand the structural, morphological and magnetic properties changes under shocked conditions. The Raman spectroscopic data reveal that the ID/IG ratio is slightly reduced under shocked conditions and the observed values are 0.78, 0.77 and 0.75 for the respective 0, 150 and 300 shocked conditions. The formation of ultra-short-range graphitic nanostructures is confirmed by HR-TEM results at the 300-shocked condition. The most convincing and supporting results for the enhancement of the degree of graphitization are found by the outcome of the magnetic properties such that the saturation magnetization (Ms) is found to be linearly reduced with respect to the number of shock pulses and the observed values are 0.869, 0.757 and 0.710 emu/g for the 0, 150 and 300 shocked conditions, respectively. The electrical resistance of the a-CQD is found to be linearly reduced with respect to the number of shock pulses due to the reduction of sp3 carbon networks. The formation of crystalline graphitic nanostructures in amorphous CQD is explained on the basis of the hot-spot nucleation mechanism. Based on the obtained Raman, HR-TEM and VSM results, during the shocked conditions, slight enhancement of the graphitization is observed; however, from the structural stability point of view, the Carbon dots have high shock resistance than that of the amorphous carbon nanoparticles, multi-wall carbon nanotubes, and reduced graphene oxide nanoparticles. Hence, the title quantum dots can be strongly considered for the applications of device fabrication.

Strong Room-Temperature Ferromagnetism of MoS2 Compound Produced by Defect Generation.

Ferromagnetic materials have been attracting great interest in the last two decades due to their application in spintronics devices. One of the hot research areas in magnetism is currently the two-dimensional materials, transition metal dichalcogenides (TMDCs), which have unique physical properties. The origins and mechanisms of transition metal dichalcogenides (TMDCs), especially the correlation between magnetism and defects, have been studied recently. We investigate the changes in magnetic properties with a variation in annealing temperature for the nanoscale compound MoS2. The pristine MoS2 exhibits diamagnetic properties from low-to-room temperature. However, MoS2 compounds annealed at different temperatures showed that the controllable magnetism and the strongest ferromagnetic results were obtained for the 700 °C-annealed sample. These magnetizations are attributed to the unpaired electrons of vacancy defects that are induced by annealing, which are confirmed using Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR).

Restoration and Transformation: The Response of Shocked and Oxidized Magnetite to Temperature

AbstractLarge impact craters on Earth are associated with prominent magnetic anomalies, residing in magnetite of the shocked target rocks and impactites. Shock experiments on magnetite suggest that up to 90% of magnetic susceptibility is lost at pressures &gt;5 GPa, but can be partially restored by post‐shock thermal annealing. The magnetic property changes are caused by shock induced grain size reduction and fragmentation, as well as domain wall‐pinning at crystal lattice defects. A recent study of granitoids from the peak‐ring of the Chicxulub crater found that annealing may occur naturally, but can also be overprinted by high‐temperature hematite‐to‐magnetite transformation in non‐oxidizing environments. In this study, we isolate the effect of defect annealing and hematite‐to‐magnetite transformation using the evolution of hysteresis, isothermal remanent magnetization components and first order reversal curve (FORC) diagrams at different high‐temperature steps. We used a laboratory‐shocked magnetite‐quartz ore, a non‐shocked naturally oxidized granite, and a naturally shocked and oxidized granite. Our findings suggest that annealing of shock‐induced lattice defects partially restores some pre‐shock magnetic behavior and causes an apparent average bulk‐sample domain state increase. Hematite‐to‐magnetite transformation creates new fine‐grained magnetite that strongly overprints the original signal, and decreases the average bulk‐sample domain state. Where annealing and hematite‐to‐magnetite transformation both occur, the new magnetite masks the annealing‐induced property restoration and apparent domain state modification in the shocked magnetite. As magnetite oxidation is a ubiquitous process in surface rocks, these findings are fundamental to understand hematite‐to‐magnetite transformation as a potential overprint mechanism, and could have broad implications for paleomagnetic interpretations.

Investigating oxidation behavior of Fe38Co38Mo8B15Cu1 alloy ribbons – structural, magnetic and Mössbauer study

This study addresses the oxidation behavior of Fe38Co38Mo8B15Cu1 alloy. Amorphous, melt-spun ribbons were heat treated in an oxygen atmosphere for different times at 350 °C, 550 °C, and 800 °C. We focus on the change in structural, thermal, and magnetic properties induced by oxygen treatment. The low-temperature heat-treated samples displayed broad, continuous, and low-intensity X-ray diffraction peaks. While no structural change was observed in the heat treatments at 350 °C both 30 min and 480 min, a significant oxide formation was observed in the heat treatment at 800 °C for 480 min. DTA/TG analysis demonstrates the weight gains and oxide formation with the temperature and time of heat treatment increase. The weight gain occurs rapidly for the sample treated for 480 min at 800 °C. A remarkable change in magnetic properties was observed. Bulk oxidation is seen by Mössbauer analysis in the heat treatment of alloy in air at 800 °C. Besides hematite, a defective CoFe2O4 phase emerged after 30 min, while after 480 min this phase was well-crystallized CoFe2O4.

Changes in Material Behavior according to the Amount of Recycled Magnetic Materials in Polymer-Bonded Magnets Based on Thermoplastics

The applications of polymer-bonded magnets are increasing within drive technology mostly because of new concepts concerning the magnetic excitation of direct current (DC) or synchronous machines. To satisfy this rising demand for hard magnetic filler particles—mainly rare earth materials—in polymer-bonded magnets, a recycling strategy for thermoplastic-based bonded magnets has to be found that can be applied to polymer-bonded magnets. The most important factor for the recycling strategy is the filler material, especially when using rare earth materials, as those particles are associated with limited resources and high costs. However, thermoplastic-based bonded magnets reveal the opportunity to reuse the compound material system without separation of the filler from the matrix. Most known recycling strategies focus on sintered magnets, which leads to highly limited knowledge in terms of strategies for recycling bonded magnets. This paper illustrates the impact of different amounts of recycling material within the material system on material behavior and magnetic properties that can be achieved by taking different flow conditions and varying gating systems into account. The recycled material is generated by the mechanical reuse of shreds. We found that a supporting effect can be achieved with up to 50% recycled material in the material system, which leads to only minimal changes in the material’s behavior. Furthermore, changes in magnetic properties in terms of recycled material are affected by the gating system. To reduce the reduction in magnetic properties, the number of pin points should be as low as possible, and they should located in the middle. The filler orientation of the recycled material is minimally influenced by the outer magnetic field and, therefore, mainly follows the flow conditions. These flow conditions are likely to be affected by elastic flow proportions with increasing amounts of recycled material.

Analyzing the impact of interlocking on non-oriented electrical steel (NOES) laminations: A microstructural and mechanical property perspective

Non-oriented electrical steel laminations are widely used in electric motor cores and are manufactured using various techniques such as cutting, punching, interlocking, and welding. These manufacturing processes can have a detrimental effect on the performance of the electric motor. Thus, in order to enhance the performance of the electric motor, it is essential to comprehend the microstructural, mechanical, and magnetic property changes resulting from manufacturing. The current study focuses on the microstructural modifications caused by interlocking, which is known to impact the core magnetic properties of motors, and its relation to mechanical properties like hardness. Six interlocked non-oriented electrical steel samples were prepared by incomplete punching at different loads from 500 N to 4000 N. Scanning Electron Microscopy (SEM) and Electron backscattered diffraction (EBSD) analysis was performed on the interlocked samples to study the microstructure and crystallographic texture near the edge whereas nanoindentation was used to determine the hardness profile. Pop-in analysis was done to study the extent of work hardening due to punching and its effect on hardness. The hardness change due to residual stress was determined, which was used to estimate the induced residual stress near the edge. It ranged from 0.04 GPa at 550 N load to 11 GPa at 4000 N load near the punched edge.

ВПЛИВ МІГРАЦІЇ ФЛЮЇДІВ НА МАГНІТНУ МІНЕРАЛОГІЮ ҐРУНТІВ

Background. The war in Ukraine arises the urgent need to intensify hydrocarbon production on its own territory in order to maintain and develop the country's energy independence. The effectiveness, low cost and relevance of the involvement are demonstrated by magnetic methods of studies of the near surface geological section and the soil for the oil and gas prospecting. Methods. The methodology of magnetic studies for the hydrocarbon prospecting is based on the methods of studying the environmental magnetism and soil, precision magnetic survey of natural systems and authigenic models of changes in magnetic mineralogy under the influence of hydrocarbon fluid migration. Results. The crucial aim is to distinguish the sources of the formation of the magnetic minerals. In most cases, soils contain minerals of natural pedogenic origin, authigenic secondary magnetic minerals, and sometimes detrital fine-coarse magnetic phases. For Ukraine, magnetite, maghemite, hematite, and goethite are the most common magnetic minerals of soils of the pedogenic origin. At the same time, the experience of conducting magnetic mineralogical analyzes of soils in the territories of oil and gas deposits indicates the presence of iron sulfides. First of all, monoclinic pyrrhotite is identified. The soils also contain accompanying hexagonal pyrrhotite, pyrite, and greigite. The results of thermomagnetic analyzes and hysteresis loops of soil samples collected at the territories of hydrocarbon deposits are presented and their mineral composition is analyzed. Conclusions. The results of the study of the impact of hydrocarbon fluid migration (microseepage) on the change in the mineral composition of soils indicate significant informativeness and the perspective of introducing the method into the complex of geological exploration works at various stages. Authigenic changes of magnetic minerals in the near surface geological section and soil, as well as natural and anthropogenic accumulation of hydrocarbon products in soils, cause changes in magnetic properties and form magnetic field anomalies.

Switching of magnetic properties by topotactic reaction in a 1D CN-bridged Ni(II)-Nb(IV) system.

Two 1D CN-bridged assemblies: the nearly straight Li2[Ni(cyclam)][Nb(CN)8]·7.5H2O (1) chains and the zigzag-shaped Li2[Ni(cyclam)][Nb(CN)8]·2H2O (2) chains, are obtained in the reaction between [Ni(cyclam)]2+ and [Nb(CN)8]4- in warm concentrated LiCl water solution. Both compounds are composed of alternating bimetallic Ni(II)-Nb(IV) chains and contain incorporated lithium cations, which compensate the negative charge of the coordination skeleton. The straight chain 1 (Ni-Nb-Ni angle = 153.2°) can be reversibly dehydrated under dry nitrogen flow at room temperature to an intermediate dihydrate phase 1d and further transformed to the zigzag-shaped chain 2 (Ni-Nb-Ni angle = 86.6°) by annealing at 150 °C. The process can be reversed by exposure to high humidity at room temperature, upon which 2 is converted back to 1. This water sorption-induced breathing effect is accompanied by changes in magnetic properties, most notably reflected in different values of saturation magnetization and critical field of metamagnetic transition, which indicate that both intra- and inter-chain interactions are affected by the structure reorganization.

Magnetic properties and electron oxidation state transition of immunomagnetic nanoparticles specifically captured with the target bacteria

Immunomagnetic nanoparticles (IMNPs) have been widely applied for the capture and concentration in the rapid detection of target bacteria. In this research, the focus was on studying the changes in magnetic properties changes of the IMNPs when they were attached to bacterial cells. These alterations in properties could facilitate an even rapid detection of the target bacteria and eliminate the need for culturing on plating media. The variation of magnetizing values, including saturated magnetization (Ms), remanent magnetization (Mr), coercivity force (Hc), and magnetic susceptibility (χm), was analysed through M-H loops. It was observed that the magnetizing properties of the IMNPs underwent changes based on the concentrations of Salmonella Typhimurium cells in the test solution. The correlation of this phenomenon was confirmed by the results of synchrotron x-ray absorption spectroscopy (XAS), which revealed electronic transition changes in the IMNPs after capturing the bacteria cells. Additionally, the electronic bands of the magnetite nanoparticle [Fe(II) and Fe(III)] were detected, indicating an electronic transformation between the Salmonella cells and the bound IMNPs. The XAS change was further verified using different cell types, such as Campylobacter jejuni which also showed electronic transformation after attaching to IMNPs. These findings suggest that IMNP-cell attachment triggered the change in the magnetic properties of IMNPs. Such insights could serve as valuable information for the development of novel rapid bacteria detection assays/devices using magnetic sensing techniques.

Exploring intermixed magnetic nanoparticles: insights from atomistic spin dynamics simulations.

Binary nanoparticles, composed of both rare-earth elements with substantial magnetic properties and transition metals known for their high magnetic ordering temperatures, hold great promise as innovative materials for novel magnetic applications. In this study, we employ an atomistic spin dynamics framework to investigate how the magnetic properties change at finite temperatures in mixed NiGd nanoparticles. We specifically examine parameters such as saturation magnetization and spin-reorientation in relation to the nanoparticle's size, which ranges from 4 nm to 16 nm, and composition. Our findings reveal that Ni75Gd25 nanoparticles demonstrate exceptional magnetic properties at finite temperatures, marked by significantly increased saturation magnetizations and magnetic ordering temperatures. In contrast, nanoparticles containing 50% and 75% Gd contents exhibit notably reduced saturation magnetizations and magnetic ordering temperatures. Theoretical findings of our study shed light on the pivotal role that the Gd content plays in determining the magnetic behaviour at finite temperatures.

Microstructure and soft magnetic properties of nanocrystalline Fe–Si–B–Cu–Nb soft magnetic alloy by laser annealing

The impact of laser annealing on the nanocrystalline Fe–Si–B–Cu–Nb soft magnetic alloy has been investigated. The experimental results showed that the microstructure of nanocrystals produced by laser annealing is comparable to that of furnace annealing. However, the annealing time plays a crucial role in determining the grain size and crystalline fraction evolution, thereby affecting both the coercivity and saturation magnetization. Nonetheless, the volume crystalline fraction of the laser annealed samples is lower than that of the furnace annealed ones due to the ultrahigh heating and cooling rate, which hinders the growth of nanocrystals and crystallization region. In addition, laser annealed samples demonstrate no distinct crystallization at high scanning speeds, even with noticeable changes in soft magnetic properties. Furthermore, the correlation between coercivity and grain size is examined, revealing a progressive decline in coercivity with a decrease in grain size. It is also found that the rule Hc ∝ D6 is also valid in laser annealing for relatively larger grains, whereas the rule becomes Hc ∝ D3 for smaller grains.