Increase In Coercivity Research Articles

Investigation of structural and magnetic properties of Al and Cu doped MnBi alloy

Alloys of Mn-Bi, MnBi-Al and MnBi-Cu were prepared by arc-melting followed by homogenization treatment. All the alloys exhibited hexagonal NiAs crystal structure. Weight fraction of the Low Temperature Phase (LTP) MnBi phase in the Mn-Bi alloy was found to be 88% with a magnetization of 51 emu/gm at 20 kOe, whereas Al and Cu doping resulted in the decrease of the weight fraction of the LTP MnBi phase as well as saturation magnetization. The coercivity is found to increase with the increase in the doping concentration. Upon ball milling the alloys, phase decomposition and a decrease in the magnetization were observed in undoped Mn-Bi alloy. On the other hand, there was no significant phase decomposition and change in the magnetization in doped MnBi alloys due to ball milling. A change in the magneto structural phase transition temperature of MnBi was observed with doping, which is attributed to the lattice modifications occurring in the MnBi system. Doped and undoped Mn-Bi alloys shows increase in coercivity with temperature. Details of investigation are presented in this paper.

Correlation between the magnetic properties and phase constitution of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys

The as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys (HEAs) were produced by vacuum arc melting. The correlation between the magnetic properties and phase constitution of the HEAs was thoroughly investigated. The results reveal that all samples contain BCC plus FCC duplex phases and the addition of Ga can promote the formation of BCC phases. Energy dispersive spectroscopy (EDS) results revealed that Cu and Ga elements are enriched in the BCC phases and they are more seriously in the phase boundary regions. Furthermore, the magnetic properties are closely related to the phase constitution of the as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs. The values of saturated magnetization (Ms), maximum magnetic flux density (Bm), remanence (Br), coercivity (Hc) and hysteresis losses (Pu) increase with the increase of the volume fraction of BCC phases, while the values of initial permeability (μi) and maximum permeability (μmax) increase with the increase of the volume fraction of FCC phases. In addition, the mechanical property of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs was also discussed in the work.

Effect of composition and powder size on magnetic properties of rapidly solidified copper-iron alloys

Powders of copper-iron alloys with composition of 10, 30 and 50 at% Fe were prepared by gas atomization process, sintered by Spark Plasma Sintering. The analysis of the as synthesized sample shows two phase FCC-Cu and BCC-Fe structure in all the three compositions independent of powder size. However, solid solution was formed between Cu and Fe during rapid solidification stages. Samples of CFA measuring ≤24 μm exhibited higher magnetic saturation (Ms) as compared to larger powder particles of the same composition due to the presence of enhanced amount of solid solution. With the increase in Fe contents, Ms and coercivity of the alloy both increase.

Microwave absorption properties of hexagonal barium doped @cip composite in wide band

M-type (BaM) hexagonal ferrite with chemical composition Ba1.0Mn0.5Co0.5Ti1.0Fe10O19 synthesized by solid state reaction. The XRD Pattern of BaM confirms the formation of hexagonal ferrite without any other impurity phases. The particle size and surface morphology has been analyzed by SEM characterization, which reveals the hexagonal morphology of Ba1.0Mn0.5Co0.5Ti1.0Fe10O19, with average size of 10 micron. The XRD pattern and SEM images of purchased Carbonyl Iron Powder (CIP) shows single phase of CIP with average size of 5 micron with spherical morphology.The XRD Pattern of BaM@CIP reveals the formation of composite, in which both phases are coexistant with CIP particles are connected with hexagonal particles of BaM to enhance the interfacial polarization due to accumulation of charges at the interfaces and improve the absorption of EM waves. The magnetic properties of pristine BaM, CIP and their composites has been studied at room temperature by Vibrating Sample Magnetometer (VSM), the M-H loop of composite sample shows increase in coercivity due to exchange spring effect produce in hard and soft magnetic composite materials. For RCS measurement, the pristine BaM ferrite and its composite with 50% (CIP) mixed with a suitable ratio of epoxy and harden, applying on a metallic surface. The Reflection loss results of composite BaM@CIP shows enhancement in widening the band width (7.75–12.5 G Hz) at a minimum thickness of 1.2 mm.

Study of structural and magnetic properties of cobalt ferrite (CoFe2O4) nanostructures

CoFe2O4 nanostructures have successfully via the auto-combustion sol-gel method. The effects of the calcined temperatures (600, 700 and 800 °C) on the structural and magnetic properties of CoFe2O4 were studied by XRD and VSM analysis. Well defined and sharp peaks corresponding to the CoFe2O4 were developed by increasing the calcination temperature in the XRD pattern. The functional groups of as prepared and calcined sample were identified by the FTIR spectra analysis. The VSM measurements showed that the saturation magnetization and coercivity increase with increasing calcination temperature. Significant differences in the magnetic properties of the CoFe2O4 nanoparticles have been observed and these differences seem to result from the calcination temperature of the spinel ferrite nanoparticles.

Influence of La content on magnetic properties of Cu doped M-type strontium hexaferrite: Structural, magnetic, and Mossbauer spectroscopy study

The present study investigates the influence of Cu2+ and La3+-Cu2+ doping on the magnetic properties of Sr1−xLaxFe12−xCuxO19 (x = 0.0–0.5) hexaferrite (SrM) compounds. The samples were prepared via facile autocombustion technique followed by sintering. X-ray powder diffraction patterns show the formation of the pure phase of M-type hexaferrite for all x. Invariance in lattice parameters was observed with only Cu2+ substitution while lattice contraction along c-axis was observed with co-doping La3+-Cu2+ in SrM. The magnetic property of these compounds is explained based on Cu2+ occupancy in the absence and presence of La3+ in SrM magnetoplumbite structure. The Cu2+ doped SrFe12−xCuxO19 sample showed a monotonic decrease in Ms value while La3+-Cu2+ showed a noticeable increase in Ms value with x. Furthermore, while coercivity of Cu2+ doped SrM reduced with x, the coercivity of La3+-Cu2+ doped SrM showed a marked 12% increase in coercivity at x = 0.1 (Hc = 4391 Oe) from that of x = 0.0 (3918 Oe). Interestingly, Cu2+ doped SrM displayed invariance in Tc ∼ 458.6 °C with x, while La3+-Cu2+ doping reduced Tc by 5% from its x = 0 (Tc = 451.9 °C) to 429.6 °C. The room temperature Mossbauer spectral analysis confirmed a Cu2+ preference for the 12k site and its occupancy is observed to be influenced by the presence of La3+ ion at the Sr2+ site.

Microstructure and magnetic properties of fcc-FePt/L10-FePt exchange-coupled composite films

The fcc-FePt/L10-FePt exchange-coupled composite films were prepared on (100)-oriented single-crystal MgO substrates using dc magnetron sputtering. The effects of fcc-FePt layer thickness and annealing temperature on microstructure and magnetic properties of fcc-FePt/L10-FePt films have been investigated. The fcc-FePt/L10-FePt film with high (001) orientation, low coercivity field, and strong soft/hard magnetic exchange-coupled interaction is obtained with 4 nm fcc-FePt layer. After annealing, there are interdiffusion and coalescence between fcc-FePt and L10-FePt layers. With increasing annealing temperature, (001) orientation and perpendicular magnetic anisotropy of the annealed films decrease, and coercivities increase. The annealed films have a relatively small value of switching field distribution.

Electroplated Fe-Co-Ni films prepared in ammonium-chloride-based plating baths

We electroplated Fe-Co-Ni films in ammonium-chloride-based plating baths, and investigated the effect of the Co content on the magnetic properties and the structural ones of the as-plated films. The coercivity increased abruptly when the Co content become more than 60 at.%. As the rough surfaces were observed in the high Co content region, we considered that degradation of the surface is a factor of the abrupt increase in the coercivity. From the XRD analysis, we found that another factor of the abrupt increase is fcc-bcc phase transformation, and concluded that we need to keep the fcc structure to obtain Fe-Co-Ni films with low coercivity.

Simultaneous magnetic investigations of Cu precipitation and recovery in thermally aged Fe-Cu alloy by first-order-reversal-curves

We have measured first-order reversal curves (FORCs) for Fe-1wt%Cu alloy thermally aged at 753 K up to 20000 min. While hardness exhibits a maximum at around 1000 min, reflecting the formation and growth of Cu precipitates, major-loop coercivity monotonically decreases and becomes almost constant above 100 min.; an increase of coercivity associated with Cu precipitation is masked by a large decrease due to recovery. On the other hand, FORC diagrams exhibit two distribution peaks at low and high switching fields after aging. While the former shifts towards a lower switching field after aging, reflecting recovery, the latter shows up after aging up to ∼1000 min, possibly due to the formation of Cu precipitates. These observations demonstrate that FORCs are useful to separately evaluate competing microstructural changes in thermally aged Fe-Cu alloy where recovery and Cu precipitation take place simultaneously.

Tailoring magnetic and dielectric properties of Co0.9Cu0.1Fe2O4 with substitution of small fractions of Gd3+ ions

This paper describes the structural, magnetic, and dielectric properties of Gd3+ substituted cobalt–copper ferrite. The influence of Gd3+ substitution on the structural, magnetic and electrical properties of cobalt–copper ferrite was investigated through various characterization techniques. Thermal analysis was carried out on the prepared gel to know the combustion and calcination temperature. The detailed structural analysis suggests that the substitution of a Fe3+ ion with a Gd3+ ion at B site results in lattice distortion, modification in crystallite size and grain size of the material. X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Magnetic measurement performed at 300 and 50 K depicts the decrease in saturation magnetization (Ms) and increase in coercivity (Hc) with Gd3+ substitution in the cobalt–copper spinel ferrite. The dielectric measurements acquired over a wide range of frequencies and temperature showed an increase in dielectric constant with increasing Gd3+ concentration.

Influence of Misorientation Angle Between Adjacent Grains on Magnetization Reversal in Nd-Fe-B-Based Sintered Magnet

To clarify the difference between the degree of alignment dependence of coercivity and the angular dependence of coercivity, the crystal orientation distribution and demagnetization curve of Nd-Fe-B-based sintered magnets with different degrees of alignment were compared. It is suggested that the increase in coercivity due to a low degree of alignment cannot be explained only by the angular dependence of coercivity. A crystal orientation analysis and in-situ observation of magnetic domains that were performed in the same area clarified that the ratio of the grain boundary where the magnetization reversal stopped became larger when the misorientation angle between adjacent grains became larger. This suggests that a grain boundary having a larger misorientation angle is one of the factors that suppresses magnetization reversal.

Effect of aging on the magnetic properties of rapidly quenched Nd-rich Nd-Fe alloys

The FexNd100-x (x = 14, 28) alloys were successfully prepared by melt-spinning. Hysteretic and thermomagnetic properties of the as-melt-spun alloys and short-aged ribbons were investigated. Both ribbons exhibit a soft magnetic behavior at room temperature but at 5 K, the coercive force (Hci) proliferated to 8.6 kOe and 11.7 kOe, respectively. Thermomagnetic measurements, Zero Field Cooling (ZFC) and Field Cooling (FC), demonstrated that the rise in magnetization of the ribbons at temperatures lower 34 K is associated with ferromagnetism of fcc Nd-Fe solid solution clusters. Positive effect of aging on the coercivity of the Fe14Nd86 and Fe28Nd72 ribbons was observed. At 300 K, Hci of the ribbons upsurge to 2 - 2.8 kOe after aging at 400 - 450°C for 15 minutes but sharply diminished after aging at temperatures higher than 500°C. It was suggested that the increase in RT coercivity during aging was as a result of the decomposition of the amorphous phase and formation of the hard magnetic Fe-rich clusters. For both ribbons aged at 500°C, the magnetic transition at 340 K was observed to be in relation to the TC of the Nd2Fe17 compound. The appearance of this soft magnetic phase in the microstructure of the aged ribbons was linked with the drastic diminution of the coercivity at that temperature.

Structural and magnetic anisotropy of directionally-crystallized ferromagnetic microwires

Amorphous ferromagnetic microwires have drawn attention primarily due to their excellent soft magnetic properties as the elements of sensors. In this work, semi-hard magnetic microwires of composition Fe4.3Co67.7Si11B14Cr3 were obtained after a process of directional crystallization from amorphous state. The XRD analysis of crushed and whole wires identified the formation of the face-centered Co-modification as the main phase of directionally crystallized core alloy, which explains a large increase in anisotropy and coercivity. The application of a magnetic field during crystallization may orient the easy anisotropy axis of crystallites along the wire. This is confirmed by the investigation of crystallite orientation with respect to the wire axis and X-rays direction in diffractometer. The obtained results revealed that the formation of crystallites in amorphous Co-rich microwires occurs with the predominant orientation of the crystallographic direction [111] along the wire axis and the direction of a magnetic field during the directional crystallization process.

Structural elucidation and magnetic behavior evaluation of Cu-Cr doped BaCo-X hexagonal ferrites

Ba2−xCuxCo2CryFe28−yO46 (x = 0.0, 0.1, 0.2, 0.3, 0.4, y = 0.0, 0.2, 0.4, 0.6, 0.8) X-type hexagonal ferrites were synthesized via micro-emulsion route. The techniques which were applied to characterize the prepared samples are as follows: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Dielectric measurements and vibrating sample magnetometer (VSM). The structural parameters i.e. lattice constant (a, c), cell volume (V), X-ray density, bulk density and crystallite size of all the prepared samples were obtained using XRD analysis. The lattice parameters ‘a’ and ‘c’ increase from 5.875 Å to 5.934 Å and 83.367 Å to 83.990 Å respectively. The crystallite size of investigated samples lies in the range of 28–32 nm. The magnetic properties of all samples have been calculated by vibrating sample magnetometer (VSM) analysis. The increase in coercivity (Hc) was observed with the increase of doping contents. It was observed that the coercivity (Hc) of all prepared samples is inversely related to the crystalline size which reflects that all materials are super-paramagnetic. The dielectric parameters i.e. dielectric constant, dielectric loss, tangent loss etc were obtained in the frequency range of 1 MHz–3 GHz and followed the Maxwell-Wagner’s model. The significant variation the dielectric parameters are observed with increasing frequency. The maximum Q value is obtained at ∼2 GHz due to which these materials are used for high frequency multilayer chip inductors.

Magnetic and dielectric behavior of praseodymium substituted barium hexaferrite

Magnetic and dielectric properties of barium hexaferrite doped with praseodymium at different calcination temperatures have been investigated. Sol gel auto-combustion method was used to synthesize Ba1-xPrxCoxFe12-xO19(x = 0.4). Fourier-transform infrared spectroscopy (FTIR), thermo-gravimetry analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and dielectric spectroscopy have been used to characterize the synthesized M-type hexaferrite. Analysis of FTIR, TGA and XRD results, confirmed the complete formation of M-type hexagonal phase with average crystallite size lying in the range 38 ± 5 nm. VSM analysis revealed the increase of coercivity, retentivity, and saturation magnetization at higher calcination temperature but under same condition decrease in the values of dielectric constant and tangent loss is observed by dielectric spectroscopy. On the basis of obtained results, Ba1- xPrxCoxFe12-xo19(x = 0.4) calcinated at 800 °C is being proposed as a harder magnetic material for manufacturing permanent magnets.

Influence of Fe substitution on structural and magnetic features of BiMn2O5 nanostructures

Nanostructures of complex oxides [BiFexMn2−xO5 (x = 0, 1, 2)] have been designed to study their structural, optical and magnetic behaviour. X-ray diffraction data (XRD) revealed orthorhombic phase with Pbam space group. Noticeable expansion in unit cell parameters has been found from BiMn2O5 (x = 0) to BiFe2O4.5 (x = 2). The observed structural changes via tuning of B-site (x = 0–2) played an important role in overall magnetic properties. Transmission electron microscopic images confirm that the average particle size of all the materials are in nano domain range with different morphologies. From optical studies, it has been found that the observed energy band gap values are strongly related to 3d electron numbers. These values appear to be larger than that reported for bulk. Isothermal magnetization plots (at 5 K) show increase in coercivity (Hc) from x = 0 to x = 2. Temperature dependent magnetization studies implied anti-ferromagnetic interactions for BiMn2O5, frustrated magnet for BiFeMnO5 and ferromagnetic behaviour for BiFe2O4.5. Ferromagnetic state of nanostructured BiFe2O4.5 is in contrast with its bulk counterparts.

Structural, dielectric and ferroelectric properties of rare earth substituted lead zirconate titanate

Rare-earth (RE) metal (Pr, Yb, Sm) ions doped lead zirconate titanate (PZT) ceramics were synthesized by the sol–gel auto-combustion technique and characterized for their structural, morphological and ferroelectric properties. The results from X-ray diffraction analysis of all these samples confirmed the tetragonal phase and only in the case of Sm doped PZT, there is pyrochlore phase. The surface morphology revealed a decrease in grain size with the RE doping with the lowest value for Yb–PZT. From the dielectric studies, a high value of dielectric constant of 2 × 105 was observed for Yb–PZT and drop in Curie temperature was observed for Pr and Sm doped PZT. The low dielectric loss and an increase in coercivity were found for Pr doped PZT which may have potential applications in memory devices.

Microstructure and magnetic characterization of the Sm-CoMn co-substituted SrCaM hexagonal ferrites

A series of Sm-CoMn substituted hexagonal ferrites with chemical composition of Sr0.85-xCa0.15SmxFe12-y(Co0.5Mn0.5)yO19 (0.00 ≤ x ≤ 0.60, (0.00 ≤ y ≤ 0.50) were synthesized by the solid-state reaction method. Microstructure and magnetic properties of the hexaferrites have been investigated by the X-ray diffraction, field emission scanning electron microscopy and a permanent magnetic measuring system. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Sm (0.00 ≤ x ≤ 0.12) and CoMn (0.00 ≤ y ≤ 0.10) contents. For the hexaferrites containing Sm (x ≥ 0.24) and CoMn (y ≥ 0.20), impurity phases are observed in the structure. The FESEM micrographs exhibit that the hexaferrites with different Sm-CoMn contents have formed hexagonal structures and the grain size of the hexaferrites remains unchanged with increasing Sm-CoMn content. The remanence (Br), Hk/Hcj ratios, and maximum energy product [(BH)max] decrease with increasing Sm-CoMn content (0.00 ≤ x ≤ 0.60, (0.00 ≤ y ≤ 0.50). Instrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) increase with increasing Sm-CoMn content (0.00 ≤ x ≤ 0.12, 0.00 ≤ y ≤ 0.10), and then decrease with increasing Sm-CoMn content (0.12 ≤ x ≤ 0.36, 0.10 ≤ y ≤ 0.30), while for the hexaferrites with Sm (x ≥ 0.36) and CoMn (y ≥ 0.30), with increasing Sm-CoMn content, Hcj increases and Hcb decreases.

Enhancement of ferromagnetic properties in composites of BaSnO3 and CoFe2O4

In this paper, we report structural and magnetic properties of BaSnO3(BSO)(1−x)–CoFe2O4 (CFO)(x) composite (with x = 0%, 1% (C1), 2% (C2) and 5% (C3) in molar ratio) synthesized using nitrate precursor method. The X-ray diffraction (XRD) pattern of the composite powder confirmed presence of both BaSnO3 with the cubic perovskite structure and CoFe2O4 with the cubic spinel structure. No signature of any other phases in pure BaSnO3, CoFe2O4 and composites have been detected either in XRD or energy dispersive X-ray (EDS) analysis. The temperature dependent zero field cooled (ZFC) & field cooled (FC) magnetization and magnetic field dependence magnetization measurements have been carried at room temperature of the pure BaSnO3. We observe a weak ferromagnetic (FM) behavior at room temperature in pure BaSnO3 even though it is non-magnetic in nature. The room temperature Raman spectroscopy and electron spin resonance measurements of the sample confirm the presence of oxygen vacancy and formation of F-center, which is responsible for the FM behavior. The oxidation state and elemental analysis have been carried out using X-ray photoelectron spectroscopy (XPS). The magnetic field dependence of magnetization of the composite samples reveal increase of saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) with increase in ferrite content in the composite. Significant enhancement in FM components is observed with lowering of temperature.

Hydrogenation caused reversible structural changes in FeCrB type metallic glasses monitored by magnetization parameters

The reversible structural changes caused by alloying with hydrogen help us to understand the relation between amorphous structure and magnetic properties. One binary FeB and three FeCrB type metallic glasses were selected for this study. The significant increase in coercivity after sample hydrogenation and its subsequent decrease during dehydrogenation are explained by changes in magnetostrictive anisotropy. Applying the Kondorsky model, the dimensional changes in stress centers caused by hydrogenation and dehydrogenation processes were determined from experimentally determined coercivity and effective anisotropy.