Effect of heat treatment on structure, magnetization and magnetostriction of Fe81Ga19 melt-spun ribbons

Structure, magnetization and magnetostriction of melt-spun Fe₈₁Ga₁₉ ribbons were investigated both before and after heat treatment. The matrix of melt-spun Fe₈₁Ga₁₉ ribbons kept a body-centered-cubic (bcc) structure (A2) at room temperature. [1 0 0] preferred orientation was formed during melt-spinning process and became stronger with the increase of the ribbon thickness. For the ribbons with a thickness of 110 μm, maximum saturation magnetostrictive strain of −189 ppm along ribbon length was obtained in the samples heat treated at 800 °C for 3 h and then quenched into water. This value was about 16% larger than that of melt-spun ones, which could be contributed to the single disordered A2 structure and the enhancement of [1 0 0]-oriented texture. However, when the ribbon samples were cooled at 2 and 0.5 °C/min after heat treatment at 800 °C for 3 h, a minor quantity of ordered D0₃ and L1₂ phase was found to precipitate in the A2 matrix, respectively, which resulted in the reduction of both magnetization and magnetostrictive strain.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Structural, magnetic properties and magnetostriction studies of Sm1−xNdxFe1.55 alloys

Structural, magnetic properties and magnetostriction studies of Sm_1−xNd_xFe_1.55 (0≤x≤0.56) alloys have been performed. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm_1-xNd_xFe_1.55 alloys with 0≤x≤0.48. The lattice parameter of alloys increases linearly with increase in Nd content while the Curie temperature behaves in the opposite way. The alloy x=0.08 exhibits a giant magnetostriction value (λ_∥-λ_⊥) of −2187 ppm at a magnetic field of 12 kOe due to the anisotropy compensation between Sm³⁺ and Nd³⁺ ions.     

Forced volume magnetostriction in Mn3.3Sn0.7C compound at room temperature

The negative volume magnetostriction in the external magnetic field for antiperovskite Mn_3.3Sn_0.7C compound is discovered. Its magnetic transition temperature from paramagnetism to ferrimagnetism is 348 K. The linear and volume magnetostrictions were investigated by measuring the change in length along the three-dimensional directions of the square samples at room temperature. Volume contraction was observed along all of the three directions throughout the whole magnetization. The value of volume magnetostriction is −44×10⁻⁶ at 1.5 T. The magnetization saturates basically at 1.5 T, however the volume magnetostriction should be higher with further increase in magnetic field.     

Structure,magnetic properties and magnetostriction of laves compounds Nd1−xPrx(Fe0.35Co0.55B0.1)2

The C15 Laves phases with composition Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ (0?x?1) have been synthesized by arc melting and subsequent annealing. The Curie temperature T_c and the saturation magnetizations M_s at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λ_a=λ_∥−λ_⊥ at room temperature for Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ alloys with 0?x?0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λ_a for the alloys with x?0.6 is positive and increases as magnetic field H increases.     

Large magnetostriction and structural characteristics of Fe83Ga17 wires

The columnar-grained structure induced by directional solidification was beneficial to improve the deformability of Fe₈₃Ga₁₇ alloy. Fe₈₃Ga₁₇ wires with diameter of 0.5∼0.9 mm were prepared successfully by hot rotary swaging and warm drawing from the directional solidified rods. The magnetostriction and microstructure of the as-drawn and the annealed Fe₈₃Ga₁₇ wires with diameter of 0.6 mm were investigated. Results demonstrated that the magnetostriction of Fe₈₃Ga₁₇ wires depended on the microstructure and the fiber texture, which were controlled by heat treatment process. The maximum magnetostriction of 160 ppm was detected in the annealed wire, which has the ideal <100> fiber texture. The phase mixture of A2 containing heterogeneous modified-DO₃ phase has beneficial effect on magnetostriction.     

Thermal-expansion anomalies and spontaneous magnetostriction of Lu2Fe17−xSix intermetallic compounds

The thermal expansion of Lu₂Fe_17−xSi_x solid solutions has been measured by X-ray powder diffraction. The magnetic ordering in all compounds within the homogeneity range (x3.4) is accompanied by a large spontaneous volume magnetostriction, distributed anisotropically over the principal axes of the hexagonal crystal structure. The volume effect ω_s in the ground state reaches 14.7×10⁻³ in Lu₂Fe₁₇ and decreases monotonously to 8.9×10⁻³ for x=3.4, following the reduction of magnetic moment. Despite a still large ω_s, the Invar behavior observed in Lu₂Fe₁₇ changes to a positive thermal expansion for x>1 due to an increasing Curie temperature.     

Magnetostriction, Curie temperature and microstructure of Tb0.29(Dy1−xPrx)0.71Fe1.97 oriented alloys

The Tb_0.29(Dy_1−xPr_x)_0.71Fe_1.97 (x=0, 0.1, 0.2 and 0.3) alloys were prepared by directional solidification method. The orientation, magnetostriction λ, Curie temperature T_c and microstructure of alloys were characterized by XRD, standard resistant strain gauge technique, VSM and SEM-EDS. The results reveal that the alloys have a preferred orientation of 〈1 1 0〉 and 〈1 1 3〉 direction when x>0. With the increase in Pr content, the T_c of alloys decreases gradually and the non-cubic phase appears, resulting in the decline of λ dramatically, from 1935.2×10⁻⁶ for x=0 to 695.9×10⁻⁶ for x=0.3 at a compressive stress of 6 MPa and a magnetic field of H=240 kA m⁻¹.     

Giant magneto-impedance effect of magnetron sputtered Ni80Fe20/SiO2/Cu composite wires

In this work, Ni₈₀Fe₂₀/Cu and Ni₈₀Fe₂₀/SiO₂/Cu composite wires of Cu core 100 μm in diameter and coated with a layer of Ni₈₀Fe₂₀ were produced by RF magnetron sputtering. In order to obtain a uniform coating, the wires were spun during sputtering. The influences of the magnetic coating and insulator thickness on the GMI effect of the composite wires were investigated. The results showed that the film thickness has a significant effect on the magnitude and the optimum frequency of the GMI effect. After the addition of an insulator layer, the MI ratio of the composite wires was observed to change with varying thickness of the insulator layer. This observed trend was attributed to the interaction between the conductive layer and the high-permeability magnetic coating.     

Coil-less fluxgate effect in (Co0.94Fe0.06)72.5Si12.5B15 amorphous wires

In this study, the coil-less fluxgate properties of the as-cast and annealed amorphous wires with the composition (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅ were investigated. As its name implies, a coil-less fluxgate is a new type of magnetic-field sensor without a coil. When the wire is periodically saturated in a magnetic field in the circumferential direction with a 30 kHz, 62 mA driving current under a 16.5π rad/m torsional strain, there is a linear variation in the second harmonic of the voltage from the wire ends as a function of the applied external DC magnetic field along the length of the wire.Current-stress annealing of each sample improved the sensitivity of the coil-less fluxgate sensor. This is the first time that it has been shown that a linear change in the output of the coil-less fluxgate sensor can be obtained using torsion annealed wire without the necessity of twisting the wire during measurement. We showed that the linear operating range of the sensor can be increased by increasing the demagnetization factor in the sensing direction, so that the coil-less fluxgate sensor can be miniaturised just by reducing the wire length.     

Rotational magnetization processes in exchange biased Ni81Fe19/Fe50Mn50 bilayers

The rotational magnetization process of an exchange coupled Ni₈₁Fe₁₉(10 nm)/Fe₅₀Mn₅₀(10 nm) bilayer was studied by Kerr microscopy. The domain processes in rotating magnetic fields near the exchange bias field H_eb are very sensitive to local variations of coupling strength and direction. A characteristic domain splitting was found that shows a remarkably different behavior for weaker and stronger coupled areas. While the magnetization in weaker coupled areas follows the rotating field for H≈H_eb, the stronger coupled areas switch back spring-like. As a result high-angle walls are formed between both areas causing rotational hysteresis.     

Relation between structure and magnetism of TixFe100−x alloys within the C14 Laves-phase stability range

We report about X-ray and magnetic investigations on polycrystalline alloys with hexagonal C14 (MgZn₂) structure of the system Ti_xFe_100−x in the concentration range 30.5x36.5 around the Laves-phase composition TiFe₂ (Ti_33.3Fe_66.6). Neighboring compositions Fe₅₀Ti₅₀ (with B2 structure) and Ti₁₅Fe₈₅ and Ti₂₀Fe₈₀ (with BCC structure) have also been investigated. From the data we establish a magnetic phase diagram for the C14 range of the system, showing a rather sharp transition from mainly ferromagnetic ordering in the range x<32 to a mainly antiferromagnetic ordering in the range x>32. The results can be made plausible microscopically by taking the site dependence of the moments into account. A revised structural equilibrium phase diagram is also given.     

Structure and magnetostriction of RFex (1.6 x 2.0) and R(Fe1−yTiy)1.8 (y 0.2) alloys (R=Dy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 x 2.0) and R(Fe_1−yTi_y)_1.8 (y 0.2) alloys (R=Dy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 x 1.85. The second phase is a rare-earth-rich phase when x 1.8, and (Dy, Tb, Pr)Fe₃ phase when x 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y 0.05, then remains almost unchanged in the range of 0.05 y 0.20. The magnetostriction of RFe_x alloys is improved when x 1.80 and reduced by increasing Fe content when x 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.     

Magneto-optical parameters of Co90Fe10 and Co50Fe50 ferromagnetic thin films for 1.3 μm integrated isolator

In order to optimize a 1.3 μm integrated optical isolator using a CoFe alloy for the non-reciprocal magneto-optical (MO) transverse Kerr effect, we have measured the optical and magneto-optical indices of Co₉₀Fe₁₀ and Co₅₀Fe₅₀ alloys grown in the Al₂O₃/Al/CoFe/GaAs multilayer structure. The optical reflectivity and MO rotation and ellipticity measurements were performed at variable incidence angle and s and p polarization of the incident light. In order to determine the optical and MO indices, the experimental data were fitted using a Matlab implementation of a standard multilayer Yeh formalism including multiple reflections. This original procedure allows precise determination of the optical and MO indices of CoFe alloys.     

Short range order transformation and magnetostriction of Fe83Ga17 ribbons

The relationship between magnetostriction and structure of melt-spun Fe 83 Ga 17 ribbons are investigated by XRD and M¨ossbauer spectrum technique(MS).As the heat-treatment temperature increases from 650℃ to 800℃,the magnetostriction coefficient of Fe 83 Ga 17 ribbon first increases and then decreases.The largest magnetostriction coefficient(578.4 ppm) is achieved in those specimens quenched at 750℃.According to the XRD and Mo¨ssbauer spectrum analysis,a small quantity of DO 3 phase is precipitated in Fe 83 Ga 17 ribbons when quenched from 650℃ and the DO 3 phase is gradually transformed into B2-like phase if quenched at higher temperature.However,both DO 3 and B2-like phases disappear when the temperature increases up to 800℃.From this point of view,B2-like phase might be beneficial to the enhancement of magnetostrictive properties of melt-spun ribbons.     

Magnetic anisotropy induced in Nd16Fe76B8 by Hf additions

Remanence, coercivity and maximum energy product (BH)_max of Nd₁₆Fe_76−xHf_xB₈ (x=0, 0.1, 0.2) magnets processed under different hydrogenation-disproportionation-desorption-recombination (HDDR) conditions, were studied. Vibrating sample magnetometry results showed that Hf-doped materials develop an important degree of anisotropy, especially for the case of solid-HDDR treatments at 800°C and 850°C, with the largest effect at 850°C. Maximum values of remanence and coercivity were observed for Hf-added samples S-HD at 850°C, and 900°C, respectively. The highest (BH)_max value was also observed in S-HD 900°C Hf-added samples. These results are discussed in terms of the expected microstructure of the intermediate HD and final HDDR processed powders.     

Giant forced volume magnetostriction in polycrystalline Tb0.3Dy0.7Fe1.95 alloys under magnetomechanical loading

The axial and transversal linear magnetostrictions (λ_∥ and λ_⊥) in [1 1 0] oriented polycrystalline Tb_0.3Dy_0.7Fe_1.95 alloys were measured simultaneously under uniaxial magnetomechanical loading to get the forced volume magnetostriction (ω=λ_∥+2λ_⊥). Despite the almost zero ω observed in Terfenol-D single crystals, it reaches up to 1000×10⁻⁶ in polycrystalline Tb_0.3Dy_0.7Fe_1.95 alloys near the saturation magnetic field under a stress above 50 MPa.     

Magnetic,structural and electrical properties of ordered and disordered Co50Fe50 films

Co₅₀Fe₅₀ films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10⁻⁶ mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co₅₀Fe₅₀ is increased, the saturation magnetization (M_s) and coercivity (H_c) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C.     

Preparation and characterizations of SiO2-coated nanoparticles of Mn0.4Zn0.6Fe2O4

Core/shell nanoparticles consisting of a magnetic core of zinc-substituted manganese ferrite (Mn_0.4Zn_0.6Fe₂O₄) and a shell of silica (SiO₂) are prepared by a sol-gel method using tetraethyl orthosilicate (TEOS) as a precursor material for silica and salts of iron, manganese and zinc as the precursor of the ferrite. Three weight percentages of the shell materials of SiO₂ are used to prepare the coated nanoparticles. The X-ray diffractograms (XRD) of the coated and uncoated magnetic nanoparticles confirmed that the magnetic nanoparticles are in their mixed spinel phase in an amorphous matrix of silica. Particles sizes of the samples annealed at different temperatures are estimated from the width of the (3 1 1) line of the XRD pattern using the Debye-Sherrer equation. The information regarding the crystallographic structure together with the particles sizes extracted from the high-resolution transmission electron microscopy (HRTEM) of a few selected samples are in agreement with those obtained from the XRD. HRTEM observations revealed that particles are coated with silica. The calculated thickness is in agreement with that obtained from the HRTEM pictures. Hysteresis loops observed in the temperature range 300 down to 5 K and Mössbauer spectra at room temperature indicate superparamagnetic relaxation of the nanoparticles.     

In-situ synchrotron X-ray absorption studies of LiMn0.25Fe0.75PO4 as a cathode material for lithium ion batteries

Recently, lithium bi-metal phosphates (LiM′M″PO₄) have been synthesized for use as cathode materials in order to increase cell voltages and electrical performances. In this work, we have substituted Mn²⁺ at the 4c site of LiFePO₄ to prepare the lithium bi-metal phosphate LiMn_0.25Fe_0.75PO₄ and have found that it greatly enhances the cell voltage. At a 0.05 C discharge rate, the cell capacity was about 153 mAhg^− 1 and the average working voltage rose to 3.53 V due to the Mn substitution. However, the capacity and working voltage both decrease as the discharge rate increases. By in-situ metal K-edge absorption analysis, it reveals that the substituted metal Mn²⁺ does not work completely at a higher discharge rate, due to poor electrical conductivity and a serious Jahn–Teller effect.