Shape Of Magnetic Hysteresis Loops Research Articles

Microstructure evolution, magnetic properties and frequency characteristics of Si-rich FeSiBCuNb soft magnetic alloy induced by annealing treatment

The influences of heat treatment on the microstructure, domain structure and magnetic characteristics of the Fe 73.5 Si 15.5 B 7 Cu 1 Nb 3 alloy were investigated. We demonstrated that the as-spun alloy exhibits high amorphous forming ability and good thermal stability with a large annealing interval between the primary and secondary crystallization peaks over 170 °C. Also, the interaction of chemical concentration fluctuations and heterogeneous nucleation is responsible for the nanocrystallization mechanism of alloy. Furthermore, the magnetic structures change from the narrow and zigzag-like branched domains to wide and regular striped domains with increasing annealing temperature, which leads to a decrease in pinning effects. Appropriate magnetic anisotropy introduced by heat-treatment process has effect on the magnetic mechanism and the shape of magnetic hysteresis loops, which adjusts the frequency characteristics. After the optimum annealing, the alloy exhibits the excellent magnetic properties including high Ms. of 135.4 emu/g and low Hc of 0.56 A/m, together with good low-frequency characteristics. • Nanocrystallization mechanism of the Si-rich Finemet amorphous alloy were studied roundly. • High volume fraction, fine, and uniformly distributed nanocrystalline structure was obtained. • Optimal Ta induced wide magnetic domains achieves high Ms., low Hc and high L. • High-temperature annealing introduced anisotropy improves high frequency characteristics.

A Study of Temperature-Dependent Hysteresis Curves for a Magnetocaloric Composite Based on La(Fe, Mn, Si)13-H Type Alloys

In the present paper, the effect of temperature on the shape of magnetic hysteresis loops for a magnetocaloric composite core was studied. The composite core, based on La(Fe, Mn, Si)13-H, was set up using three component disks with different Curie temperatures. The magnetic properties of the components and the outcome composite core were determined using a self-developed measurement setup. For the description of hysteresis loops, the phenomenological T(x) model was used. The presented methodology might be useful for the designers of magnetic active regenerators.

H−T phase diagram of rare-earth–transition-metal alloys in the vicinity of the compensation point

Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic field and in the vicinity of the compensation temperature have so far been explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic rare-earth ion approximation and taking into account rare-earth (Gd) magnetic anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice is larger than that of the $d$-sublattice, the tricritical point can be at higher temperature than the compensation point. The obtained phase diagram explains the observed anomalous hysteresis loops as a result of high-field magnetic phase transition, the order of which changes with temperature. It also implies that in the vicinity of the magnetic compensation point the shape of magnetic hysteresis loop is strongly temperature dependent.

Critical hydrogenation effect on magnetic coercivity of perpendicularly magnetized Co/Pd multilayer nanostructures

Low dimensional materials of perpendicularly magnetized [Co(0.5 nm)/Pd(3 nm)] multilayer, including continuous thin film, nanodots and nanodot-chains were prepared for the investigation of reversible hydrogenation effect on the magnetic and optical properties. For the continuous film, after hydrogenation the magnetic coercivity (Hc) was enhanced by 47% and the Kerr intensity was significantly reduced to 10% of the pristine value. In nanodots, hydrogenation led to 25% reduction of Hc and Kerr intensity as well. For nanodot-chains, the shape of magnetic hysteresis loop was modulated by hydrogenation. The hydrogenation and desorption completed within few seconds in nanodots.

Synthesis and magnetic properties of (CoNiPsoft/CoPhard) n multilayers

Magnetic interactions in Co-Ni-P multilayers consisting of alternating magnetically soft and magnetically hard layers are investigated experimentally. Variations in the shape of magnetization hysteresis loops upon the conjugation of magnetically soft and hard layers are found, along with saturation field oscillations that depend on the number of layer pairs.

Modification in Structure, Phase Transition, and Magnetic Property of Metallic Gallium Driven by Atom–Molecule Interactions

The present work supports a novel paradigm in which the surface structure and stacking behavior of metallic gallium (Ga) were significantly influenced by the preparation process in the presence of organic small molecules (ethanol, acetone, dichloromethane, and diethyl ether). The extent of the effect strongly depends on the polarity of the molecules. Especially, a series of new atom-molecule aggregates consisting of metallic Ga and macrocyclic hosts (cyclodextrins, CDs) were prepared and characterized by various techniques. A comprehensive comparative analysis between free metallic Ga and the Ga samples obtained provides important and at present rare information on the modification in structure, phase transition, and magnetic property of Ga driven by atom-molecule interactions. First, there is a notable difference in microstructure and electronic structure between the different types of Ga samples. Second, differential scanning calorimetry analysis gives us a complete picture (such as the occurrence of a series of metastable phases of Ga in the presence of CDs) that has allowed us to consider that Ga atoms were protected by the shielding effect provided by the cavities of CDs. Third, the metallic Ga distributed in the aggregates exhibits very interesting magnetic property compared to free metallic Ga, such as the uniform zero-field-cooled and field-cooled magnetization processes, the enhanced responses in magnetization to temperature and applied field, and the fundamental change in shape of magnetic hysteresis loops. These significant changes in structural transformation and physical property of Ga provide a novel insight into the understanding of atom-molecule interactions between metallic atoms and organic molecules.

Relaxation study of RE-123 materials with different types of pinning defects

The well known fact that the shape of magnetic hysteresis loop (MHL) is closely related with relaxation phenomena, is documented on a wide range of different pinning structures. It is shown that the normalized relaxation rate can be directly calculated from characteristics of the MHL. In the case of known additive contributions to the global moment, the relaxation behaviour is accessible for these individual pinning mechanisms. Thus relaxation studies have exactly the same information value as magnetic hysteresis curves.

The remagnetization process in spin-valve structures

The process of magnetization reversal in ultrathin magnetic trilayer is analyzed. It is shown that the shape of magnetization hysteresis loops and the giant magnetoresistance essentially depend on the relative magnitudes of magnetic parameters of the top and the bottom layers. New types of hysteresis loops are found for characteristic relative magnitudes of the parameters. Analysis of the dependence of the shape of hysteresis loops on the magnitude of interlayer exchange is performed. The phase diagram which determines the regions of existence of characteristic hysteresis loops for different relative magnitudes of the uniaxial anisotropy constant and exchange constant J 1 is constructed.

Field-cooled magnetization of YBa 2Cu 3O 7− δ superconductors

DC susceptibility as a function of temperature was measured in both field-cooled cooling and warming modes in magnetic fields in the range of 10 mT⩽μ 0H a⩽7 T on a variety of YBa 2Cu 3O 7− δ samples, comprising different single crystals, melt-processed bulks and polycrystalline samples, with and without KClO 3 addition. The Meissner curves measured at a field of 1 mT reveal that all the samples are of a single phase. However, with increasing applied fields, the superconducting transitions of the single crystals and the melt-processed samples develop kinks, and above 4 T, even a secondary transition can be observed. At low temperatures, the field-cooled moment increases in all samples, except the KClO 3-doped samples, where a clear decrease is observed. These features are discussed in detail. Further, we discuss the correlation between the kinks in the DC susceptibility and the appearance of the fishtail shape of magnetization hysteresis loops.

Features of magnetization reversal in trilayer nanostructures

The process of magnetization reversal in an ultrathin magnetic trilayer is analyzed. It is shown that the shape of magnetization hysteresis loops and the giant magnetoresistance essentially depend on the relative magnitudes of magnetic parameters of the top and bottom layers. Hysteresis loops are found for characteristic relative magnitudes of the parameters. Analysis is performed of the dependence of the shape of hysteresis loops on the magnitude of interlayer exchange. A phase diagram is constructed, which determines the regions of existence of characteristic hysteresis loops for different relative magnitudes of the uniaxial anisotropy constant and exchange constant J1.

Variable shape of magnetic hysteresis loops in the Chinese loess-paleosol sequence

Shape of magnetic hysteresis loops of the Chinese loess-paleosol sequence is variable with low-field susceptibility and is weakly constricted in samples with intermediate susceptibility (~1.0 × 10−6 m3/kg). The analyses of the hysteresis loops show that both low- (ferrimagnetic) and high-coercivity (antiferromagnetic) components are present and the ferrimagnetic component dominate the magnetic characteristics. The ratio of ferrimagnetic over antiferromagnetic minerals (S ratio) and the superparamagnetic fraction increase with increasing susceptibility. Neither simple two-component mixtures of ferrimagnetic and antiferromagnetic minerals nor of single-domain and superparamagnetic grains fully explain the constricted hysteresis loops. We interpret the variation of the loop shape with susceptibility in the following way. When the ratio of the ferrimagnetic to antiferromagnetic contribution is relatively low (low susceptibility), the broad loop is controlled by lithogenic ferrimagnetic and antiferromagnetic minerals. For samples with intermediate susceptibility values, constricted shape originates from an addition of a broad loop from the lithogenic fraction and a narrow loop from a pedogenic fraction with high superparamagnetic content. Then with further susceptibility increase, the constricted shape almost disappears and the loop is dominated by the pedogenic fraction. The variation of hysteresis loop shape with susceptibility can be a useful indicator of the degree of pedogenesis for loess-paleosol samples.

Modeling of Barkhausen noise in magnetic core material: Application of Preisach model

The Preisach model is utilized to model Barkhausen noise in magnetic core materials. Barkhausen noise is generated each time the magnetization goes through a sudden change at a local site in the core material. In this article we examine the relationship between the shape of magnetization hysteresis loops to details of Barkhausen noise levels or excitations. On the basis of hysteresis loops alone it may be possible to profile the noise spectrum of a magnetic core.

Shape of magnetic hysteresis loop measured on superconducting Bi-2223/Ag tapes

An anomalous position of the central peak of magnetic hysteresis loops (MHL) was observed in (Bi, Pb)-2223/Ag tapes by a vibrating sample magnetometer at positive external fieldBext for dBext/dt<0. It can be explained by joint effect of both intra-and intergranular currents and by regarding the value of the local magnetic fieldBi at the circumference of flat, well oriented grains in the tape. While in majority of the sample volumeBi is delayed behindBmax, just at the grain circumferences (the bottleneck for intergrain currents)Bi is considerably ahead ofBext.

The effect of viscous forces in the flux-line lattice of high-Tc superconductors on the shape of magnetic hysteresis loops

The half-height M of magnetic hysteresis loops in superconductors (directly related to the induced critical current) is larger for larger rates of sweep, B=dBext/dt, of the external magnetic induction, Bext. If the flux-line (FL) motion is determined only by thermally activated flux creep then the induced magnetization M, increases linearly with the logarithm of B. In this paper, the author analyses another mechanism affecting the distribution of FL due to viscous forces. This mechanism yields a linear increase of M with B. Measurements on YBaCuO single crystals initially show a close to logarithmic dependence (corresponding to the dominant flux creep mechanism of FL motion), but the dependence turns towards higher values of M at higher speeds of FL motion. This deviation can be partly attributed to viscous forces in a moving FL lattice.

Comparison between conventional flux creep in constant magnetic field and the effect of creep on the shape of magnetic hysteresis loops in high-Tc superconductors

The effect of the magnetic induction sweep rate B= delta Bext/ delta t on the shape of magnetic hysteresis loops, in particular on the induced magnetic moment m ( implies/implied by critical current jc) was calculated directly from the basic mechanism of thermally activated flux creep introduced by Anderson taking jc constant through the sample. It was found (a) that m changes linearly with ln mod B mod , and (b) that delta m/ delta ln mod B mod is equal to - delta m/ delta ln t in conventional relaxation at Bext=constant. Similar results were obtained recently from a phenomenological model using differential susceptibility chi to characterize the effect of sweeping Bext.