δM Curves Research Articles

Carbon-Doped Co2MnSi Heusler Alloy Microwires with Improved Thermal Characteristics of Magnetization for Multifunctional Applications.

In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.

Effect of an aluminum layer deposited with magnetron sputtering on magnetic and remanence properties of Sr-hexaferrite

This work deals with the effect that aluminum deposited on the strontium hexaferrite has on the magnetic and remanence properties. The aluminum was deposited using magnetron sputtering and the deposit thickness was varied through two deposition times. The presence of the aluminum was corroborated by X-ray diffraction and scanning electron microscopy. The magnetic characterization showed an increment in remanence squareness (Mr/Ms), while the maximum energy product (BHmax) exhibited a large increment regarding the hexaferrite without aluminum. Isothermal remanent magnetization (IRM) and direct current demagnetization (DCD) curves were measured for two samples with different amounts of deposited aluminum and for the strontium hexaferrite without aluminum. The Henkel plots and δM curves were discussed in the Stoner-Wohlfarth framework. Results show a diminishing of demagnetizing-like interactions as the deposited aluminum increases on the hexaferrite surface. This behavior suggests that aluminum promotes the emergence of a type of exchange interaction with a magnetizing effect.

Analysis of Vibrating Sample Magnetometer (VSM) data of Brantas river sediments using HYSITS

Several vital activities in East Java are supported by the Brantas River, ranging from irrigation, supply of water raw materials, to industry. Along with the growing population, has the potential to increase the pollution that occurs in the Brantas River. VSM data was taken from the measurement results in Brantas River sediments. The aim of this study is to analyze the VSM measurement data in the Brantas River using the HYSITS script. The analysis was carried out to determine the type of magnetic domain contained in the Brantas river sediment. HYSITS program is used to provides a deeper and better analysis and interpretation. The results show that HYSITS produces 2 curves besides hysteresis loop graphic, that is 1st derivative of ΔM curve and ΔM curve. From the Hysteresis curve of sample, it is known that the Saturation Magnetization (Ms ) value are 5.3262 - 5.998587 emu/g, the Saturation Remanent Magnetization (Mrs ) value are 1.1537 - 1.545586 emu/g, the Magnetic Coercivity (Bc ) value are 0.0188 - 0.020784 T, and Magnetic Remanent Coercivity (Bcr ) are 0.059891 - 0.0815. Result of the analysis indicates that the magnetic minerals in Brantas River are strongly suspected to represent ferrimagnetic minerals with Pseudo-Single Domain (PSD).

The effect of the Mo addition on the magnetic properties and phase constituents of the Ce-(FeCo)–B ribbons

The effect of molybdenum (Mo) addition on the magnetic properties and phase constituents of Ce14Fe78-xMoxCo2B6 (x = 0–1.25 at %) ribbons has been investigated. The investigated ribbons have been prepared by melt spinning technique at different velocities. Samples were studied in as-cast state and after annealing. The results reveal that the addition of Mo in Ce14Fe78-xMoxCo2B6 ribbons and the subsequent annealing improves the magnetic properties. Mo acts as inhibitor of the growth of crystalline grains and reduces the volume fraction of the undesirable non-magnetic phases. As a result, the coercivity of Ce14Fe78-xMoxCo2B6 ribbons increases with the increase of Mo content from x = 0 to x = 1.25 at%, while the remanence remains unchanged up to 0.75 at% Mo content and after this value slightly decreases. Analysis of the δM curves showed that a suitable content of Mo improves the exchange coupling interaction. The optimum magnetic properties, i.e. coercivity, Hc = 6.1 kOe, remanence (Br) = 5.2 kG and energy density (BH)max = 4.92 MGOe, were obtained in ribbons with 1.0 at% Mo. The addition of Mo lead to an improvement of the magnetic properties of CeFeB-based ribbons making them good candidate precursors for the preparation of permanent magnets without heavy critical rare earths.

A fatigue model based on M-integral in notched elastic–plastic material

In this paper, an innovative fatigue model is investigated based on the concept of M-integral in notched elastic–plastic material. The contribution of notch and plastic zone damage to the lifetime of material are taken into account in the present fatigue model. The new form of fatigue damage evolution rate (dAD/dN) and fatigue driving force (ΔM) are introduced, where AD deontes the equivalent damage area of notch, plastic zone and cracks, N is the number of cycles, and ΔM corresponds to the M-integral range per load cycle. The fatigue experimental evaluations of a typically elastic–plastic material (e.g., No. 45 steel) with a circular notch have been carried out to validate the effectiveness of the present fatigue model. For experimental study, the change of the total potential energy (CTPE) is introduced to measure the value of M-integral. The results demonstrate that dAD/dN shows an apparent power law relation with ΔM in notched elastic–plastic material. The slope n and intercept λ of lg(dAD/dN)-lg(ΔM) curve has linear correlation with the initial notch radius R, but not with applied stress σ. Moreover, the model can clearly describe the two-stage process from the initiation of microcracks to the growth of macrocracks in notched body. It is concluded that the proposed fatigue model based on M-integral can accurately predict the fatigue lifetime of the notched elastic–plastic material.

Isothermal Remanent Magnetization (IRM) and Direct Current Demagnetization (DCD) Curves for Nanocrystalline Sm-Y-Co Alloys

Magnetization curves were measured using the methods of isothermal remanent magnetization (IRM) and direct current demagnetization (DCD) for nanocrystalline Sm0.5Y0.5Co5 alloys. The study of magnetic properties for nanocrystalline Sm0.5Y0.5Co5 alloys was performed with the Physical Property Measurement System (PPMS). The alloys exhibited a high remanent coercivity of 2.1 MA/m. The ratio of magnetic susceptibilities for nanocrystalline Sm0.5Y0.5Co5 alloys was χd/χr = 4.6, indicating the presence of magnetic interactions in the alloys. Nanocrystalline Sm0.5Y0.5Co5 alloys with magnetic interactions were studied by measuring ΔM curves against the magnetic field, and the alloys showed dipolar and exchange interactions.

The relationship between magnetic properties and morphology of nanocomposites

The ZnFe2O4/CoFe2O4 nanofibers and nanoparticles were prepared by electrospinning and hydrothermal methods respectively. Through the analysis of hysteresis loops, it was found that the nanofibers have higher saturation magnetization coercivity and remanence than nanoparticles, which was due to the shape anisotropy of nanofibers. Through the analysis of the switching field distribution and δM curve, it was found that there was exchange-spring behavior between soft and hard magnetic phases, and nanofibers had stronger exchange interaction than nanoparticles.

Magnetic and microstructural properties of Nd7Fe67B22Mo3Zr0.5Ti0.5 nanocomposite magnets produced by injection casting

The microstructure and magnetic properties of Nd7Fe67B22Mo3.5-xZr0.5Tix (x = 0, 0.5, 1.0) nanocomposite magnets prepared by annealing the amorphous precursors have been investigated and presented. The Nd7Fe67B22Mo3Zr0.5Ti0.5 alloy exhibits high glass forming ability as well as good hard magnetic properties in magnetic rods of 2 mm in diameter and 40 mm in length. As-cast Nd7Fe67B22Mo3Zr0.5Ti0.5 amorphous rod shows soft magnetic properties. Annealing induces promising hard magnetic properties as Br = 0.55 T, iHc = 965 kA/m and (BH)max = 47.6 kJ/m3. Electron microscopy elucidates a microstructure composed of magnetically soft α-Fe (27 nm), Fe3B (24 nm) and hard Nd2Fe14B (50 nm) magnetic grains. The single phase hard magnetic characteristics of M-H loop and δM curve yield the existence of strong exchange coupling interactions between the magnetically soft and hard phases.

Preparation and magnetic properties of the Sr-hexaferrite with foam structure

This work reports an optimal way to fabricate strontium hexaferrite with porous-reticulated structure using a variation of the replication technique and taking two different precursors, one obtained from the coprecipitation and the other from the ceramic method. Changes made to the original replication technique include the addition of Arabic gum as binder, and the addition of ethylene glycol to form the ceramic sludge. In addition, some parameters such as the relation between solid material and liquid phase, the quantity of binder and the heat treatment were varied to obtain high quality magnetic foams. Two polymeric sponges were used as patterns, one with average pore size of 300μm diameter and the other with 1100μm. The characterization of the samples included the analysis of the structure and phase purity, the magnetic properties, the remanence properties, magnetic interactions and the microstructural characteristics. Results indicate that both, the powder precursors and the polymeric pattern play an important role in the configuration of the foam structure and this configuration has an important influence on the dipolar interactions which tend to demagnetize the samples. In addition, it was analyzed the behavior between the minimum value of the δM curves and the hysteresis properties.

Magnetic self-assembly for the synthesis of magnetically exchange coupled MnBi/Fe–Co composites

Exchange coupled hard/soft MnBi/Fe–Co core/shell structured composites were synthesized using a magnetic self-assembly process. MnBi particles were prepared by arc-melting, and Fe–Co nanoparticles were synthesized by an oleic acid assisted chemical reduction method. Grinding a mixture of micron-sized MnBi and Fe–Co nanoparticles in hexane resulted in MnBi/Fe–Co core/shell structured composites. The MnBi/Fe–Co (95/5wt%) composites showed smooth magnetic hysteresis loops, enhanced remanent magnetization, and positive values in the ΔM curve, indicating exchange coupling between MnBi and Fe–Co particles.

Magnetic and structural properties of MnBi multilayered thin films

Magnetic and structural properties of MnBi films with thicknesses up to 50 nm were investigated. Thin films of the MnBi LTP (Low Temperature Phase) were fabricated onto silica-glass substrates by sputter-deposition of Bi/Mn multilayer, followed by a subsequent annealing at about 550 °C for 30 min. Coercivity of such thin films is higher than 15 kOe, even though the film thickness is about 10 nm. These thin films show the preferential growth of c-axis of the LTP along the film normal. Moreover, high resolution transmission electron microscopy indicates that the LTP regions of 30–50 nm in size are physically isolated by Bi. The magnetization reversal mechanism of such a LTP region is mainly governed by a coherent rotation mode based on the δM curve measurement.

Intercrystallite magnetic interactions and properties of nanostructured magnetic materials (review)

Intercrystallite magnetic interaction in nanostructured films for magnetic recording and magnetic microelectronics and also its correlation with magnetic properties and performance characteristics of materials is analyzed on the basis of investigation of δM curves, data of Mossbauer spectroscopy, the anomalous Hall effect, etc.

Fe64B22.8Nd6.6Y3.9Nb2.7 bulk nanocomposite magnets with improved size and magnetic properties

Abstract

Microstructure and magnetic interactions in Pr–Fe–Co–Zr–Nb–B magnets

The microstructure and interactions between grains in Pr9Fe52Co13Zr1Nb4B21 magnets produced by short time annealing (at 983K for 5min) of rapidly solidified samples were investigated. The specimens were produced in the form of suction-cast 1mm diameter rods, 1mm thick plates and 3mm outer diameter (o.d.) tubes. The X-ray diffraction analysis and Mössbauer spectroscopy shown presence of hard magnetic Pr2Fe11.2Co2.8B and paramagnetic Pr1+xFe4B4 crystalline phases diluted within the amorphous matrix in all samples. The microstructure was studied using TEM microscopy. Furthermore, rates of irreversible magnetization changes upon the change of external magnetic field H, were studied. In order to characterize interactions between grains of crystalline phases the δM curves were also constructed from recoil data.

Study of the magnetic interaction in nanocrystalline Pr–Fe–Co–Nb–B permanent magnets

The magnetic properties of an isotropic, epoxy resin bonded magnets made from Pr–Fe–Co–Nb–B powder were investigated. The magnetization reversal process and magnetic parameters were examined by measurements of the initial magnetization curve, major and minor hysteresis loops and sets of recoil curves. From the initial magnetization curve and the field dependencies of the reversible and irreversible magnetization components derived from the recoil loops it was found that the magnetization reversal process is the combination of the nucleation of reversed domains and pinning of domain walls at the grain boundaries and the reversible rotation of magnetization vector in single domain grains. The interactions between grains were studied by means of δM plots. The nonlinear behavior of δM curve approve that the short range intergrain exchange coupling interactions are dominant in a field up to the sample coercivity.The interaction domains and fine magnetic structure were revealed as the evidence of exchange coupling between soft α-Fe and hard magnetic Nd2Fe14B grains.

Low temperature magnetic hardening in self-assembled FePt/Ag core-shell nanoparticles

The FePt/Ag core-shell nanoparticles with different Ag shell thickness have been fabricated using a seed mediated technique. The core-shell nanoparticles are annealed at temperatures ranging from 350 to 600 °C for 30 min in vacuum. The magnetic measurement demonstrates that the FePt/Ag core-shell nanoparticles show a better chemical ordering tendency with a magnetic hardening temperature of 400–450 °C, which is almost 100 °C lower than that of pure FePt nanoparticles. Negative peaks on the δM curves of the annealed FePt/Ag core-shell nanoparticles demonstrate that the predominant interparticle interactions are dipolar type rather than exchange coupling one. Besides, the FePt/Ag core-shell nanoparticles show both sensitive plasmonic and superparamagnetic properties. The present results indicate that our composite nanoparticles are very promising from the viewpoint of the optoelectronics and biomedical applications.

Intercrystalline magnetic interaction and hysteresis characteristics of high-coercivity cobalt-based alloy coatings

δM(H) curves and the time dependences of the magnetization and the rotational hysteresis losses are used to analyze the effect of intercrystalline magnetic interaction on the magnetization reversal and the hysteresis characteristics of nanostructured cobalt-based alloy coatings, which manifest themselves in a change in the relations between the rotation and displacement of reversible and irreversible processes and between thermally activated and field processes.

First-order reversal curves of magnetic recording tapes

The interaction and its variation between magnetic grains in two kinds of magnetic recording tapes are investigated by first-order reversal curves (FORC) and the δM method. The composition and microstructure of the samples are characterised by x-ray diffraction and scanning electron microscope. The FORC diagram can provide more accurate information of the interaction and its variation, but the δM curves cannot. The positive interaction field and the large variation of the interaction field have opposite effects on the δM curve.

Adjust the resonance frequency of (Co90Nb10/Ta)n multilayers from 1.4 to 6.5 GHz by controlling the thickness of Ta interlayers

In this work, the static and high frequency magnetic properties of (Co90Nb10/Ta)n multilayers have been investigated. The results show that the in-plane uniaxial magnetic anisotropy fields can be adjusted from 12 to 520 Oe only by decreasing the thickness of Ta interlayers from 8.0 to 1.8 nm. As a consequence, the resonance frequencies of the multilayers continuously increased from 1.4 to 6.5 GHz. It was found that the changes in the in-plane uniaxial anisotropy field are ascribed to the interlayer interactions among the magnetic layers by investigating the δM(H) curves.

Enhancement of Magnetic Properties for FePt Nanoparticles by Rapid Annealing in a Vacuum

FePt nanoparticles with uniform compositions were synthesized by a modified coreduction process of FeCl2·4H2O and Pt(acac)2 and then rapidly annealed in a vacuum under temperatures ranging from 500 to 700 °C. We found that the coercivities of the FePt nanoparticles were greatly enhanced by the rapid annealing in a vacuum. Negative peaks on δM curves for the annealed FePt nanoparticles demonstrate that the predominant interparticle interactions are dipolar-type rather than exchange coupling ones, which indicates that the rapid annealing in a vacuum can prevent the agglomeration of the nanoparticles. Through the heat treatment of annealing in a vacuum, monodispersed Fe46Pt54 nanoparticles with a high coercivity of 9230 Oe were successfully fabricated.