Wasp-waisted Hysteresis Loops Research Articles

Magnetic properties of chains of spherical nanoparticles with cubic magnetic anisotropy: A Monte Carlo study

Monte Carlo techniques are used to simulate magnetic properties of chains of identical, spherical, single-domain, ferromagnetic nanoparticles with cubic magnetocrystalline anisotropy. Nanoparticles are placed along a straight line with their positions and directions of anisotropy axes fixed in changing external magnetic field. Hysteresis curves as well as zero field cooled (ZFC) and field cooled (FC) experiments are simulated for chains of different lengths, i.e. differing in both: the number of particles and inter-particle distances. Strongly anisotropic dipole–dipole inter-particle interactions lead to significant differences in system’s response to the external magnetic fields oriented parallel and perpendicular to the chain, and further, to the occurrence of wasp-waisted hysteresis loops. We compare results for chains that differ in the size of particles they are built of. To get the idea about the quantitative scale of the discussed phenomena we assume values of magnetocrystalline anisotropy constants for fcc-Co.

Magnetic characterization of self-assembled nanostructures in cobalt ferrites using first-order reversal curve (FORC) analysis

Magnetic ceramics are important for numerous technologically relevant applications with a detailed understanding of structure, property, and processing inter-relationships playing a critical role in tailoring magnetic properties. Spinel ferrites are a particularly interesting class of magnetic ceramics of chemical formula AB2O4, with applications including biomedical hyperthermia and high frequency electrical power conversion. In this contribution, we seek to investigate a unique class of Co-ferrites in which spinodal decomposition can produce a ferrite nanocomposite with chemistry and stress state fluctuating within the interior of crystalline grains on the nm-scale, resulting in corresponding fluctuations of intrinsic magnetic properties as well as exchange and magnetostatic interactions. Structural and magnetic characterization of spinel ferrite samples are carried out (1) in the as-milled state prior to thermal processing, (2) after chemical and structural homogenization with a thermal calcination step, and (3) in the spinodal decomposed state following a subsequent annealing treatment within the Co-ferrite miscibility gap. Of note is the formation of a wasp-waisted hysteresis loop which emerges for the spinodal decomposed Co-ferrite sample, indicative of more complex magnetization reversal processes at relatively large applied fields than for homogeneous Co-ferrite samples of similar particle size and identical nominal chemistry. First order reversal curve (FORC) analysis is applied to further characterize the magnetization response, and a conventional interpretation of observed features in the FORC contrast is presented to discuss potential dominant magnetization mechanisms. The work described here represents the first application of FORC to spinodal decomposed magnetic ceramics and provides a strong foundation for future investigations seeking to quantitatively describe the impacts of nm-scale chemical, structural, and magnetic fluctuations on magnetization processes in ferrite spinel nanocomposite systems.

ПЕРІОДИЧНІСТЬ ЗЕМЛЕТРУСІВ У КАСПІЙСЬКОМУ МОРІ

Magnetic minerals form or alter in the presence of hydrocarbons, making them a potential magnetic proxy for identifying hydrocarbon migration pathways. We concentrate in the precision magnetic mineralogical analyzes to understand what magnetic minerals in soil from the hydrocarbon fields are responsible for the magnetic signal. To illustrate the results of our studying, we consider the study area of the hydrocarbon deposits near the village Balabanivka, Bogodukhiv district, Kharkiv region. A collection of soil samples is represented by deep medium-humus chernozems. The thermomagnetic analyzes, hysteresis parameters, and isothermal remanent magnetization curves (IRM) were studied for the samples collected near the well (point PR 28) and at the area located out of the hydrocarbon influence zone (point PR 0403). To study the thermomagnetic parameters, different types of the magnetization and magnetic susceptibility (MS, χ), and hysteresis loops we used the Variable Field Translation Balance (VFTB) instrument. The results are confirmed by the highest values of the gas geochemical parameters. The MS variations at temperatures ranging from 200 to 400 ˚C may reflect the presence of either iron sulphides or maghemite. The magnetite occurs for all soils. The wasp-waisted hysteresis loops identified either a mixture of two magnetic minerals (magnetite and hematite) and the admixture of the superparamagnetic and larger grains of the same minerals.

Optical and magnetic properties of Sm-doped BiFeO3 nanoparticles around the morphotropic phase boundary region

The crystal structure, photocatalytic activity, and ferromagnetic properties of Sm-substituted (Bi1−xSmxFeO3, x = 0.05, 0.10, 0.15, 0.20) nanoparticles were systematically investigated within the entire Sm substitution region. The morphotropic phase boundary (MPB) consisting of a rhombohedral phase, orthorhombic interim phase (Pna21), and orthorhombic phase with 0.1 ≤ x ≤ 0.2 is constructed and confirmed by x-ray diffraction and Raman spectra with new vibration modes at ∼310 cm−1. The photocatalytic activity and ferromagnetism are improved around the MPB region (x = 0.10). Meanwhile, the wasp-waisted hysteresis loops are present around the MPB region. Wasp-waisted hysteresis loops have the features of low hysteresis loss in low magnetic fields and are helpful in designing some multiferroic devices.

Wasp – Waisted loop and spin frustration in Dy2−xEuxTi2O7 pyrochlore

The Raman spectroscopy and AC and DC magnetization of Dy2−xEuxTi2O7 pyrochlore materials have been investigated. A systematic shift in all phonon modes with higher Eu content in Dy2−xEuxTi2O7 observed in Raman spectra confirms the successful substitution of Dy3+ ion by Eu3+ ions. High concentration of Eu induces the exchange interactions between atoms and alters the crystal-field interactions in Dy2−xEuxTi2O7. Rich Eu content samples (x = 1.5, 1.8 and 1.9) show the existence of wasp-waisted hysteresis loop which is explained on the basis of dipolar field, anisotropy exchange interaction and spin frustration present in the samples. Interestingly, AC susceptibility shows two single ion spin freezing transitions corresponding to Dy3+ and Eu3+ ions respectively in Eu rich samples only.

Thickness-Dependent Magnetism in Epitaxial SrFeO3-δ Thin Films

Strained oxygen-deficient perovskite SrFeO $_{3 - \delta }$ (SFO) films have been epitaxially grown by pulsed laser deposition (PLD) on SrTiO3 (STO) (001) substrates. Oxygen deficiency of the films in comparison with the stoichiometric perovskite SrFeO3 is manifested in the increased lattice parameter, $c = 3.97$ A, the decreased mass density, $\rho = 4.825$ gcm−3, and the presence of Fe3+ cations. The SFO perovskite structure is monoclinically distorted with an increase of the film thickness, resulting in the reduction of the total magnetic moment. A wasp-waisted hysteresis loop and a negative exchange bias are observed for the 69 nm thick film due to the possible magnetic sublayers arising from a proper monoclinically distorted surface layer and a substrate-locked core layer.

Peculiarities of magnetic ordering in the S=5/2 two-dimensional square-lattice antimonate NaMnSbO4

An orthorhombic compound, NaMnSbO4, represents a square net of magnetic Mn2+ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and density functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with TN about 44 K, which is preceded by a short-range one at about 55 K. In addition, a non-trivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of 2D square lattice model with the main exchange parameter J = -5.3 K, which is in good agreement with density functional analysis, NMR and ESR data.

Tailoring magnetic properties with interfacial spins interaction for bundled cobalt ferrites nanowires

Abstract Bundled cobalt ferrites (CoFe2O4) nanowires (BNWs) were successfully prepared by nanocasting pathway with ordered mesoporous SiO2 (SBA-15) templates. The well-dispersed CoFe2O4 nanowires (NWS) were separated from CoFe2O4 BNWs by centrifugal technology. Microstructure characterization indicated that CoFe2O4 BNWs and NWS possessed the same diameter and similar length. Thus, the influence of surface spins interaction between neighboring nanowires on the magnetic properties could be distinguished and discussed excluding the difference of morphology. Both samples presented ferromagnetism with the wasp-waisted hysteresis loops and the exchange bias effect was observed above 100 K. The surface spins interactions between the neighboring nanowires not only recombined the mismatch spins at the surface to form antiferromagnetic surface, but also inhibited the shape anisotropy of nanowires, leading to the decrease of saturation magnetization and coercivity of CoFe2O4 BNWs. The wasp-waisted hysteresis loops was attributed to the low temperature spin reorientation caused by the inclined spin on the surface of nanowires.

Mineral magnetic properties of granodiorite, metagabbro and microgabbro of Petermann Island, West Antarctica

The research focuses on studying the magnetic properties and mineralogy of iron-bearing minerals of granodiorite, metagabbro, and microgabbro of Petermann Island, West Antarctica. The predominant iron-bearing minerals of the rocks are ilmenite, magnetite, and iron sulphides. Magnetite in metagabbro and microgabbro is pointed out to be present as two morphological types with different grain size and morphology. The rocks owe their magnetic properties to the presence of different amounts of magnetite with the Curie temperatures of 570–575°C for granodiorite, 555–560°C for metagabbro and 560–565°C for microgabbro. Magnetite in the rocks is stable under heating to 650°C. A slight decrease in magnetisation at 350–400°C is attributed to the conversion of maghemite or maghemite-like phase into hematite. Variation of the magnetite content within each sample has a strong expression in the saturation magnetisation. The latter increases in sequence: granodiorite (0.8–1.3 Am2/kg), microgabbro (1.8–3 Am2/kg) and metagabbro (3.1–3.5 Am2/kg). The saturation magnetisation of rocks increases with the increasing content of iron. However, the inverse relation is observed for metagabbro and microgabbro due to the replacement of titanite for magnetite in the latter. The magnetic fraction of microgabbro reveals the wasp-waisted hysteresis loop suggesting bimodal size distribution. According to X-Ray Diffraction, the characteristic peaks (d-spacing) of pure magnetite are identified for magnetic fraction of granodiorite and metagabbro, while magnetite of microgabbro form stable intergrowth with titanite and chlorite.

The wasp-waisted hysteresis loop and exchange bias in multiferroic BaNiF4

Multiferroic BaNiF4 has been fabricated by hydrothermal method. The bifurcation between zero field cooling (ZFC) and field cooling (FC) temperature dependent magnetization (M-T) curves starts at 150 K, indicating the 2D antiferromagnetic (FM) transition. A further upturn of magnetization has been observed below 68 K in FC M-T curve, corresponding to the emergence of 3D AFM structure. Wasp-waisted hysteresis loop was observed under 130 K, which is explained by that the AFM aligned net spins from the canting of neighboring AFM spins due to Dzyaloshinskii-Moriya interaction can be easily aligned by the magnetic field. Exchange bias effect was detected below 70 K, which has been interpreted by the magnetization pinned by the spontaneous polarization through magnetoelectric coupling.

Wasp-waisted magnetism in hydrothermally grown MoS2 nanoflakes

Two-dimensional semiconducting materials are emanating as a requisite group of materials for future nanoscale electronics and optoelectronics. Particularly, transition-metal dichalcogenides like molybdenum disulphide (MoS2), a semiconducting inorganic counterpart of graphene have intrigued intensive interest as two-dimensional materials due to its novel functionalities. In this work, the utilization of high pressure and low temperature hydrothermal method offers a facile, versatile synthetic tool for MoS2 nanoflakes formation without the addition of any surfactants. Our experimental results resolve the formation of hexagonal phase, well-ordered stacking of S–Mo–S layers, quantum confinement and interlayer interaction. The strong spin–orbit coupling in MoS2 provides enthralling optical and magnetic properties. A large optical absorption in 400–700 nm region and strong luminescence provide evidence for the indirect to direct band gap transition in MoS2. Magnetic measurement results reveal ferromagnetism for all the MoS2 nanoflakes and also indicate an increase in saturation magnetization with increase in duration of growth. In addition, a wasp-waisted hysteresis loop was also observed for the first time in MoS2 nanostructures indicating multimodal population, increased grain growth and MoS2–MoO3 coupling. Our findings provide important insights into the future applications of MoS2 in high-performance nanodevices and spintronics.

Simulation of Wasp-Waisted Magnetic Hysteresis Loop for NiCoP-Coated BaFe12O19–Polystyrene Bilayer Composite Film

Brillouin function was modified to model the wasp-waisted magnetic hysteresis loop for soft-magnetic NiCoP-coated hard-magnetic M-type ferrite BaFe12O19 polystyrene (PS) bilayer composite film taking into account the effective applied magnetic field due to localized impurity phases and significant change in the azimuthal angle of the magnetic moment due to the formation of bilayer structure of film by the addition of PS. It is shown that there is a good fit to the experimental data observed in wasp-waisted magnetic hysteresis loop. The analysis shows that the forward magnetization and reversal process are typical.

‘Anomalous’ magnetic fabrics of dikes in the stable single domain/superparamagnetic threshold

‘Anomalous’ magnetic fabrics in dikes that appear to indicate flow into the wall confound many workers. Here, we present extensive magnetic data on five dikes from Tenerife, Canary Islands, and use these to interpret the causes of the anomalous fabrics. Comparison of the anisotropy of magnetic susceptibility (AMS) and anhysteretic magnetization (AARM) results show that, in some cases, the anomalous fabrics are caused by single-domain grains, which produce AMS fabrics perpendicular to the grain elongation, whereas AARM fabrics are parallel. To check this, hysteresis experiments were used to characterize the domain state. These show most are mixtures of pseudo-single-domain or single-domain plus multi-domain particles, but many have wasp-waisted hysteresis loops, likely indicating mixed populations of stable single-domain and superparamagnetic grains. First-order reversal curves were used to better characterize this and show mixtures of stable single-domain and superparamagnetic grains dominate the magnetic signal. Magnetic particles at the stable single-domain/superparamagnetic threshold are unstable at timespans relevant to the analytical techniques, so they produce complicated results. This suggests that anomalous AMS fabrics in dikes cannot simply be attributed to elongated stable single-domain particles and that mixtures of the different grain types can produce hybrid fabrics, in which the fabrics are neither perpendicular or parallel to the dike plane, that are difficult to interpret without extensive magnetic analysis.

Template-free synthesis of Nd0.1Bi0.9FeO3 nanotubes with large inner diameter and wasp-waisted hysteresis loop

One-dimensional (1D) nanotubes of Nd0.1Bi0.9FeO3 (NBFO) with an inner diameter of ∼50 nm were synthesized via sol-gel based electrospinning without template assistant. The phases, morphologies, crystalline structures, and magnetic properties of these 1D nanostructures were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and SQUID, respectively. It was found that the calcination condition plays a crucial role in determining the morphologies and the magnetic properties. Interestingly, these 1D NBFO nanotubes exhibit wasp-waisted magnetic hysteresis with a lower coercivity and larger saturation magnetization, which were prevalent in natural rocks and artificial composite materials. The origin of these wasp-waisted hysteresis loops was discussed.

Microemulsion synthesis and magnetic properties of hydroxyapatite-encapsulated nano CoFe2O4

Hydroxyapatite-encapsulated cobalt ferrite (CoFe2O4) nanopowders were synthesized by one step microemulsion method. The powders were characterized by X-ray Diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer. TEM results showed that nanoparticles calcined at 700°C have core–shell morphology. It was found that the resultant phases, morphology and magnetic properties of the samples depend on calcining temperature. The synthesized nanoparticles showed a maximum saturation magnetization of 7.8emu/g with a wasp-waisted hysteresis loop. The magnetion was reduced by increasing calcining temperature to 900°C. This reduction is due to the reaction of cobalt ferrite with hydroxyapatite which leads to CaFe12(PO4)8(OH)12 phase.

High-pressure synthesis, structural and complex magnetic properties of the ordered double perovskite Pb2NiReO6

The ordered double perovskite Pb2NiReO6 has been prepared at 6 GPa and temperatures ranging from 1273 to 1373 K. Its crystal structure determined by X-ray powder diffraction and selected area electron diffraction shows monoclinic symmetry with centrosymmetric space group I2/m (a = 5.6021(1) Å, b = 5.6235(1) Å, c = 7.9286(1) Å and β = 90.284°(1)). High angle annular dark field microscopy studies reveal the existence of compositional microdomains. The compound displays a re-entrant spin-glass transition from a ferrimagnetic ordering below T(N) ~ 37 K between the Re(+5) and Ni(+3) (high spin configuration) magnetic sublattices to a spin-glass configuration. Magnetic field dependent magnetization measurements revealed wasp-waisted hysteresis loops at 5 K. These shaped features originate from the antiferromagnetic/ferromagnetic (AFM/FM) competing interactions.

Coercivity Control of Variable-Length Iron Chains in Phthalocyanine Thin Films

The magnetic characteristics of iron phthalocyanine thin films are studied with a vibrating sample magnetometer, identifying a ferromagnetic transition temperature at 4.5 K. The metal ions at the center of the molecule are self-assembled along chains producing quasi one-dimensional magnetic chains of variable length in the thin films. The average chain length is varied from 20 to 300 nm via substrate temperature during deposition. Below the critical transition temperature, the magnetization curves have the shape of wasp-waisted or constricted loops. The in-plane chain length modulates the coercivity and saturation field and larger grains increase the coercivity significantly. First-order reversal curves of the wasp-waisted hysteresis loops reveal a long narrow strip that suggests a broad distribution of coercive fields and weak intergrain magnetic interactions. These findings are also supported through simulations based on the Preisach model.

A unique magnetic behavior and dielectric properties of Bi 0.9– xLa 0.1Ca xFeO 3 nanoparticles at room temperature

Ca 2+ and La 3+ ions co-doped BiFeO 3 nanoparticles, Bi 0.9– x La 0.1Ca x FeO 3 (BLCFO x ) ( x=0, 0.10, 0.13, 0.17 and 0.20), were prepared by a sol–gel method. X-ray diffraction analysis showed that the average grain size of the prepared samples was in the range of 24–19 nm. The lattice structure of the nanoparticles transformed from orthorhombic to cubic with Ca 2+ ions substitution increased. Dielectric properties were measured up to high frequency ∼80 MHz. It was found that the co-doping of suitable amount of La 3+ and Ca 2+ ions was helpful to improve the dielectric properties of the samples. Magnetic properties of the samples were improved and all the co-doped samples presented a wasp-waisted hysteresis loop, which was rarely reported in BFO. Characteristics of wasp-waisted hysteresis loops show low hysteresis loss in low magnetic fields, and are helpful to design some multiferroic devices.

Paleomagnetic and magnetic fabric studies of the San Gaspar ignimbrite, western Mexico—constraints on emplacement mode and source vents

Paleomagnetic and magnetic fabric data for the 4.8 Ma San Gaspar ignimbrite, one of the largest in western Mexico, are used to investigate the source vents, emplacement mechanism and tectonics. Rock magnetic properties from distant parts of the ignimbrite are similar, suggesting relatively homogeneous mineralogy of the unit. Isothermal remanence and continuous susceptibility-temperature experiments point to low to medium-Ti titanomagnetites as the main magnetic carriers. Hysteresis ratio parameters of most samples fall in the pseudo-single-domain grain size region; wasp-waisted hysteresis loops were identified corresponding to high H cr / H c values. Stepwise thermal and alternating field demagnetization shows that secondary components are completely removed below 20 mT or 400 °C. Thereafter, the characteristic component is isolated with small within-site dispersion of mean direction ( α 95 < 10° at 7 out of 10 sites). The within-site consistency of directional features of magnetic fabric supports that the ignimbrite welded and cooled in situ and was probably emplaced in a NW-SE rift zone from a single eruption center located south or east of a younger Pleistocene caldera in the area. Paleomagnetic, rock magnetic and ore microscopy data support the hypothesis that the extensive and widespread ignimbrite deposits in western Mexico correspond to a major explosive volcanic phase in the Pliocene.

Investigation on electro-strain effect in Rh-doped BaTiO3 single crystals

The electric-field-induced strain in Rh-doped BaTiO3 single crystals increases with increasing ageing time at 80℃. After 27 days' ageing, the strain can reach 1.11% under bipolar field cycling conditions. However, the strain under mo nopolar field cycles is strongly dependent on the drive frequency and reaches as high as 0.95% at frequency of 0.01Hz. The hysteresis loop (P-E curve) of the aged sample is similar to a wasp-waisted hysteresis loop. Ageing can significant ly improve the electro-strain effect in the Rh-doped BaTiO3 crystal a nd make t he BaTiO3 crystal a promising and lead-free material for novel applic ations in ultra-large strain and nonlinear actuators.