Magnetic properties and microstructure of nanocomposite(Nd,Pr)–Fe–B ribbons by doping Nb element

Effects of Nb addition and annealing treatmen on magnetic properties and microstructure of(Nd0.4Pr0.6)9Fe76–xNbxB15(x = 0–4) ribbons were systematically investigated by means of vibrating sample magnetometer(VSM) and X-ray diffraction(XRD). The extra phases with nonmagnetic(Nd,Pr)1.1Fe4B4phase and metastable compound(Nd,Pr)2Fe23B3 crystallized during quenching the Nb-free alloy. Moreover, the nonmagnetic(Nd,Pr)1.1Fe4B4phase does not diminish during the following annealing treatment. The addition of Nb to(Nd,Pr)–Fe–B alloy suppresses metastable(Nd,Pr)2Fe23B3 and nonmagnetic(Nd,Pr)1.1Fe4B4phases. The intrinsic coercivity increases from 397 kA m-1for the Nb-free sample to1,091 kA m-1for the 4 at% Nb-doped sample optimally annealed. The Nb-free sample has the magnetic properties with Js= 1.04 T, Jr= 0.66 T, and(BH)max= 43.5 kJ m-3By comparison, the magnetic properties of the 4 at% Nbdoped sample were 0.97 T, 0.68 T, and 65.7 kJ m-3respectively. The significant improvement of magnetic properties mainly originates from the finer grains of the ribbons by introducing Nb.     

Structure and magnetic properties of TbCu_7-type melt-spun Sm–Fe–B alloys

The melt-spun SmFe_(12)B_x(x = 0, 0.50, 0.75,1.00, 1.25 and 1.50) ribbons were prepared at 40 m·s~(-1),and their structure and magnetic properties were studied by powder X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and transmission electron microscopy(TEM). XRD results indicate that SmFe_(12)B_x alloys with 0.50 ≤ x ≤ 1.00 are composed of single-phase TbCu_7-type structure. Moreover, it is found that the boron addition can inhibit the emergence of soft magnetic phase a-Fe and result in the increase in the axial ratio c/a. After annealing at 650 ℃ for 0.5 h, the metastable phase TbCu_7 initially decomposes into the stable phase Sm_2Fe_(14)B(Nd_2Fe_(14)B-type) and a-Fe. The value of magnetic moment per Fe atom increases slightly from 1.75 uB for boron-free sample to 1.80 uB for the x = 0.75 sample and then decreases again.In addition, the best magnetic properties of maximum energy product [(BH)_(max)] of 14.56 kJ·m~(-3), coercivity(H_(cj))of 172.6 kA·m~(-1) and remanence(B_r) of 0.45 T are obtained for the SmFe_(12)B_(1.00) alloy. Based on transmission electron microscopy(TEM) results, the average size of grains is around 197 nm for B-free sample and decreases to 95 nm for x = 1.00 sample, indicating that the addition of boron can refine grains.     

Effects of substrate temperature and annealing treatment on the microstructure and magnetic characteristics of TbDyFe films

A series of TbDyFe films were prepared by DC magnetron sputtering. The effects of substrate temperature and annealing temperature on the phase structure and the magnetic properties of the sample films were investigated. The an-nealing treatment has a significant influence on the microstructure and the magnetic properties of the sample. The results obtained by XRD indicate that the films deposited at a temperature lower than 525℃ are amorphous and have an easy magnetization direction perpendicular to the film plane. An RFe2 phase is formed in the sample annealed at 550℃ and the residual phases observed are Fe and rare earth oxide. The magnetic properties Hc and Mr/Ms of the film annealed at 550℃ obtain the maximum values,for which the formation of the RFe2 phase is mainly responsible. An annealing treatment leads to a rotation of the sample’s easy axis from being parallel to the film surface to becoming vertical.     

Effect of annealing parameter on microstrucmre and magnetic properties of cold rolled non-oriented electrical steel

The microstructure and magnetic properties of cold rolled non-oriented electrical steel, annealed at 200-1 000℃ for 0-240 min with different heating rates, were investigated by optical microscopy, scanning electron microscopy, Epstein frame, and transmission electron microscopy. The results show that the magnetic properties of cold rolled non-oriented electrical steel can be improved by controlling the annealing process to obtain uniform coarse grains with critical sizes after the recovery, recrystallization and growth of grains. Additionally, the annealing temperature influences the magnetic properties more significantly than annealing time, and with the increase of heating-up rate during the annealing process, the magnetic properties of the cold rolled non-oriented electrical steel increase.     

Microstructure and high temperature mechanical properties of laser rapidly formed Ti-6Al-4V alloy

Several tensile samples were prepared using laser rapid forming （LRF） with Ti-6Al-4V alloy as powder material, and the samples were annealed. The microstructure and high temperature mechanical properties of laser formed Ti-6Al-4V alloy through annealing treatment were investigated. The short-term and long-term tensile tests at 350 ℃ were performed. The results show that the microstructure of LRF samples consists of the large columnar prior β grains which grow epitaxially from the substrate along the deposition direction. There are Widmanstaitten a laths in prior β grains, but a laths in annealed microstructure are coarser, and their aspect ratio is lower than that in as-deposited microstructure. In addition, the prior β grain boundary is also coarsened and broken off through the annealing treatment. The high temperature mechanical properties of the annealed LRF samples exceed those of casting alloy significantly, especially the stress-rupture lifetime reaches 661.7 h even while the test stress increases from initial value of 490 MPa to the final stress of 800 MPa gradually.     

Magnetic properties of Nd_2Fe_(14)B/α-Fe nanocomposite magnets with yttrium addition

The phase evolution and magnetic properties of Nd9?xYxFe72Ti2Zr2B15 (x = 0,0.5,1,and 2) melt-spun nanocomposite ribbons were studied.It is found that Y addition not only enhances the formability of amorphous phase in the alloy,but also stabilizes the amorphous phase during the annealing treatment.The appropriate content of Y addition effectively enhances the remanence (Jr) of the annealed sample.The residual amorphous intergranular phase in the annealed sample optimizes the squareness of the loop,resulting in an larger maximum energy product (BH)max.The best magnetic properties,Jr = 0.78 T,Hci (coercivity) = 923.4 kA/m,and (BH)max = 98.5 kJ/m3,were obtained from the Nd8YFe72Ti2Zr2B15 ribbon spun at Vs = 4 m/s and annealed at 700°C for 10 min,which is composed of Nd2Fe14B,α-Fe,and amorphous phase.     

THE INFLUENCE OF PRECURSOR VARIABLES ON THE PHASE FORMATION,MICROSTRUCTURE AND TRANSPORT PROPERTY OF Bi—2223／Ag TAPES

The Bi-2223/Ag tapes were prepared with spray-died powders, which are of different particle sizes and phase assemblages by varying the annealing time in pure oxygen. Longer time annealing degraded the reactivity of precursor powder, which in turn resulted in an incomplete conversion from precursors to Bi-2223, porosity core and misaligned grains in fully processed tapes. The best Jc in short pressed samples varied from 29.7 to 47kA/cm2 for the tapes made from different powders.     

Effect of heat treatment on structure and magnetic properties of Fe65.5Cr4Mo4Ga4P12C5B5.5 bulk amorphous alloy

This study deals with the Fe65.5Cr4Mo4Ga4P12C5B5.5 ferromagnetic bulk amorphous alloy. XRD analysis showed an amorphous structure of the as-cast sample. The same method revealed that, after annealing at 973 K for τ=10 min, the sample displayed a crystalline structure with crystalline phases formed. The crystallization process of the alloy was examined by DTA analysis. It was shown that crystallization took place in the temperature range between 810 K and 860 K with the exo-maximum peak temperature at 846 K with a heating rate of 20 K·min-1. The method also showed that, at temperatures ranging from 753 K to 810 K, the alloy exhibited the properties of supercooled liquids. A correlation between heat-induced structural changes and magnetic properties of the alloy was determined by thermomagnetic measurements. Maximum magnetization M=3.7 Am2·kg-1 of the alloy was reached after its annealing at 733 K for τ=10 min. Upon annealing, the alloy exhibited a relaxed amorphous structure. Annealing the alloy above the crystallization temperature led to a decrease in bulk magnetization. After annealing at 973 K for τ=10 min, the bulk magnetization of the alloy was M'=0.45 Am2·kg-1. Accordingly, after crystallization and formation of new compounds, the magnetization of the alloy was decreased by a factor of about 7.7. The strength of the magnetic field applied during the measurements was H=10 k A·m-1. The samples were tested for changes in the microstructure and hardness of both the amorphous phase and the resulting crystalline phase.     

Influence of Continuous Bending Process on Texture Evolution and Mechanical Properties of AZ31 Magnesium Alloy

Mg–3Al–1Zn alloy sheets have been deformed by continuous bending(CB) to investigate the effects of pro cessing parameters(bending angle and repetitive passes) on the texture and formability. The samples exhibited a bimoda microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing. The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD, and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing Compared with the as-received sample, the yield strength of CBA-120-2 sample significantly decreased from 183 to112 MPa, and a smaller r-value and a larger n-value were obtained. The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm, increased by about 135%. The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.     

Microstructure and mechanical properties of AZ91-Ca magnesium alloy cast by different processes

The microstructure and mechanical properties of magnesium(Mg) alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2 wt.% Ca(AZX912) Mg alloy samples prepared by gravity casting(GC), squeeze casting(SC) and rheo-squeeze casting(RSC), respectively, was carried out. The results show that α-Mg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 °C to 200 °C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.     

Effect of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> doping on the structure,magnetic properties and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

The (La_0.7Ca_0.3MnO₃)_1x /(NiFe₂O₄) _x (x = 0 to 0.09) composites were prepared using a conventional solid state reaction method. The structural, magnetic properties, and electrical properties of LCMO/NFO composites were investigated using X-ray diffraction, scanning electron microscopy, field cooled DC magnetization, and magnetoresistance (MR) measurements. The resistivity measured as a function temperature demonstrates that the pure LCMO and x = 0.01 samples display metal to semiconductor transitions. However, the composites of x > 0.03 samples clearly present the electrical behavior as an insulator/semiconductor type behavior. It was observed that the resistivity of the samples increased systemically with an increase of the NFO content. From the MR measurements, it was found that the MR effect is enhanced for x = 0.01 with a NFO composition. In all, the spin-polarized tunneling and the spin-dependent scattering may be beneficial for an improved low-field magnetoresistance effect. These phenomena can be explained by the segregation of a new phase related to NFO at the grain boundaries or surfaces of the LCMO grains.     

Structure and magnetic properties of mechanically alloyed Tb0.2Pr0.8（Fe0.4Co0.6）1.93 and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 was synthesized by mechanical alloying (MA) and subsequent annealing process. The structure and magnetic properties of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 were investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 alloy with the single phase of MgCu₂-type structure can be successfully synthesized by MA method. The sample annealed at 450°C is found to have a coercivity of 196 kA/m at room temperature. An epoxy/Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an applied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite combines a high magnetostriction with a significant coercivity, which is a promising magnetostrictive material.     

Microstructural characteristics of Nd2Fe14B/α-Fe nanocomposite ribbons bearing Nb element

The effects of Nb on the microstructure and magnetic properties of (Nd_0.9Dy_0.1)_9.5Fe_79-xCo₅Nb_xB_6.5 (x = 0, 1) nanocomposite magnets were investigated. A fine and uniform microstructure was achieved for the ribbons annealed at 710°C for 4 min, enhancing the interaction coupling between grains and improving the magnetic properties. The results of three-dimensional atom probe (3DAP) indicated that Fe-Nb-B intergranular phase existed at the grain boundaries, suppressing the grain growth during the crystallization process. The coercivity was improved from 224 to 643 kA/m for the modification of the microstructure.     

Crystallization behaviour and high coercivity of （Nd,Pr）（13）Fe（80）Nb1B6 melt-spun ribbons

Amorphous (Nd,Pr)₁₃Fe₈₀Nb₁B₆ ribbons were crystallized at 670–730°C for 5–25 min to study the effects of isothermal crystallization on their behavior and magnetic properties. XRD results indicate that the isothermal incubation time is 12, 5, and less than 5 min at 670, 700, and 730°C, respectively. High coercivities, with the maximum value of _i H _c = 1616 kA/m at 700°C for 19 min, measured by a physical property measurement system, are obtained in the crystallized ribbons. This is mainly attributed to the addition of Pr and Nb, because Pr₂Fe₁₄B has a higher anisotropic field than Nd₂Fe₁₄B, and Nb enriched in the grain boundary regions can not only reduce the exchange-coupling effects among hard grains, but also impede grain growth during the crystallization process. In addition, it should also be related to the characteristics of the furnace that the authors designed.     

Effect of magnetic field on the morphology and fine structure of low-temperature martensite phase in a ferromagnetic Ni<Subscript>2.08</Subscript>Mn<Subscript>0.96</Subscript>Ga<Subscript>0.96</Subscript> alloy

The morphology and fine structure of high-temperature austenitic and low-temperature martensitic phases in a ferromagnetic Ni_2.08Mn_0.96Ga_0.96 alloy and the effect of magnetic field on the peculiarities of the martensite formation have been studied. The Ni_2.08Mn_0.96Ga_0.96 alloy in the initial cast and annealed states was found to undergo martensitic and magnetic phase transformations at temperatures M _s = 280 K, M _f = 265 K, A _s = 280 K, A _f = 295 K, and T _C = 375 K, respectively. Above M _s, the alloy is in a metastable premartensitic state, which leads to a characteristic diffuse scattering and tweed contrast when studying by electron microscopy. An applied magnetic field of up to 600 kA/m was found to affect the martensitic transformation in the alloy. The field application leads to changes in the morphology and fine structure of martensite due to orientation along the field direction of the magnetizations of the energetically advantageous (in terms of the directions of the magnetization vectors) c domains of the existing orientation variants of the martensite crystals having a packet pairwise-twinned morphology. The martensitic structure of the Ni_2.08Mn_0.96Ga_0.96 alloy already formed previously during cooling is not affected by an external magnetic field with a strength of up to 600 kA/m.     

Formation of ferromagnetism in pseudobinary PrNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (2.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 5) solid solutions

The structure and magnetic properties of the PrNi_{5 − x} Cu _x alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu₅ type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu₅ the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi_{5 − x} Cu _x system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr³⁺ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi_{5 − x} Cu _x intermetallic compounds.     

Enhancement of room-temperature magnetoresistance in La<Subscript>0.6</Subscript>Dy<Subscript>0.1</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The samples of La0.6Dy0.1Sr0.3MnO3/(Ag2O)x/2(x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30) were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature(M-T) curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is compar...     

Electrochemical properties of carbon-coated LiFePO<Subscript>4</Subscript> and LiFe<Subscript>0.98</Subscript>Mn<Subscript>0.02</Subscript>PO<Subscript>4</Subscript> cathode materials synthesized by solid-state reaction

Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0. 98Mn0. 024/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt. ％ carbon coating (x=3, 7, 11, 15) at γ=0. 2C, 2C (1C=170 mAh·g-1) between 2. 5 and 4. 3 V were investigated. The measured results mean that the LiFePO4 with 7 wt. ％ carbon coating shows the best rate performance. The discharge capacity of LiFe0. 98Mn0. 02PO4/C composite is found to be 165 mAh·g 1 at a discharge rate, γ=0. 2C, and 105 mAh·g-1 at γ=2C, respectively. After 10cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh·g-1 and 98 mAh·g-1 at γ=0. 2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.     

Magnetocaloric effect of （Gd1-xCex）Co2 compounds in low magnetic fields

The phases in the compounds (Gd_1−x Ce _x )Co₂ with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 were investigated by X-ray diffraction, and the magnetocaloric effect for x = 0–0.4 was studied by magnetization measurements. The samples are almost single phase with a cubic MgCu₂-type structure for x = 0–0.5. The magnetization decreases with an increase in Ce content. There is almost no magnetic transition for x = 0.5 at 100–350 K. The Curie temperature (T _c) of the (Gd_1−x Ce _x )Co₂ compounds with x from 0.1 to 0.4 are 350, 344, 340, and 338 K respectively. The maximum magnetic entropy change is 2.34 J·kg⁻¹·K⁻¹ when x = 0.3. The results of Arrott plots show that the magnetic phase transition is second-order magnetic phase transition in these compounds.     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.