Magnetic transitions and magnetostrictive properties of Laves compounds Sm0.88Nd0.12(Fe1−xCox)1.93

The structure, magnetic and magnetostrictive properties of Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 (0≤x≤1.0) alloys have been investigated. The alloys have the cubic MgCu₂ structure over the whole composition range and the lattice parameter a decreases with increasing x. For 0≤x≤0.2, substitution of Co for Fe slightly increases the saturation magnetization M_s and Curie temperature T_c, while further substitution causes a decrease in both M_s and T_c. The spin reorientation is observed, and a phase diagram for the spin configurations of the Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 system is determined. The spontaneous magnetostriction λ₁₁₁ increases as x is increased, while a monotonic decrease of the saturation magnetostriction λ_s with x originates from the increase of λ₁₀₀ with opposite sign to that of λ₁₁₁, which may be caused by the filling of the d band due to Co substitution.     

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.     

Magnetostriction and magnetic anisotropy of (Sm,Ce)Fe2 compounds

The structural, magnetic and magnetostrictive properties of Sm_1−xCe_xFe₂ (0≤x≤1) Laves compounds have been investigated. The magnetostriction coefficient λ₁₁₁ and the anisotropy of the Sm_1−xCe_xFe₂ compounds decrease with increasing Ce content. The decreasing of anisotropy results in an enhancement of the anisotropic magnetostriction at low magnetic fields for the compounds with a small amount of Ce substituted for Sm.     

A survey on the effect of vanadium content on the magnetoelastic properties of YFe12−xVx alloys

Experimental results on the thermal expansion and magnetostriction of YFe_12−xV_x (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5 T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5 T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe_12−xV_x compounds.     

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.     

High magnetostriction at low fields of (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds

The structure and magnetostriction of the (Tb_1−xDy_x)_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λ_a (λ_a=λ_‖-λ_⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ_a being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compounds, which could become a kind of promising magnetostrictive material.     

A study on magnetoelastic properties of Tb3 (Fe28−xCox) V1.0 (x=0, 3, 6) compounds

In this work, The magnetoelastic properties of polycrystalline samples of Tb₃ (Fe_28−xCo_x) V_1.0 (x=0, 3, 6) intermetallic compounds are investigated by means of linear thermal expansion and magnetostriction measurements in the temperature range of 77–515 K under applied magnetic fields up to 1.5 T. The linear thermal expansion increases with the Co content. The well-defined anomalies observed in the linear thermal expansion coefficients for Tb₃ (Fe_28−xCo_x) V_1.0 (x=0, 3, 6) compounds are associated with the magnetic ordering temperature for x=0 and spin reorientation temperatures for x=3, 6. Below transition temperatures, the value of the longitudinal magnetostriction (λ_Pa) at 1.6 T increases with Co content.     

Structure and magnetostriction of Tb0.2Pr0.8(Fe0.4Co0.6)1.93−xCx intermetallic compounds

The structure and magnetostriction of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93−xC_x intermetallic compounds were studied by X-ray diffraction and magnetic measurements. Almost a single cubic Laves phase forms in the alloys for x ≤0.20, and a small amount of C can inhibit the formation of the 1:3 phase. The lattice parameter increases when 0≤x≤0.15, while the T_c and the spontaneous magnetization decreases with increasing x. The lattice parameter decreases slowly when 0.15≤x≤0.30, while the T_c decreases evidently with increasing x. The magnetostriction λ_a (=λ_∥-λ_⊥) is improved at low magnetic fields at room temperature for the compounds with 0.05≤x≤0.10, indicating that these C-containing compounds are promising magnetostrictive materials.     

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In_1−xFe_x)₂O₃ (x = 0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In_1−xFe_x)₂O₃ powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In_1−xFe_x)₂O₃ samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe²⁺ and Fe³⁺ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49-1.73 μ_B/Fe and the Curie temperature around 783 K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe²⁺ and Fe³⁺ ions via an electron trapped in a bridging oxygen vacancy.     

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.     

Effect of Sm,Co codoping on the dielectric and magnetoelectric properties of BiFeO3 polycrystalline ceramics

Multiferroic Bi_0.95Sm_0.05Fe_1−xCo_xO₃ (x=0−0.1) ceramics were prepared by the rapid liquid phase sintering method. For all the samples studied, the dielectric constant and dielectric loss decrease with increasing frequency in the range from 1 kHz to 1 MHz. It shows that the dielectric constant of Bi_0.95Sm_0.05FeO₃ at 10 kHz is about forty times larger than that of pure BiFeO₃. This dramatic change in the dielectric properties of Bi_0.95Sm_0.05Fe_1−xCo_xO₃ (x=0−0.1) samples can be understood in terms of the space charge limited conduction associated with crystal defects, which was indicated by the increase of magnetoelectric effect with doping Co³⁺ under applied magnetic field from 1 to 8 kOe. It was believed that the ferroelectric polarization enhancement comes from the exchange interaction between the Sm³⁺ and Fe³⁺ or Co³⁺ ions for Bi_0.95Sm_0.05Fe_0.95Co_0.05O₃ at room temperature.     

A magnetic, magnetostrictive and Mössbauer study of Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys

The effect of Pr substitution for Dy on the magnetization, magnetostriction, anisotropy and spin reorientation of a series of Tb_0.3Dy_0.7−xPr_x(Fe_0.9Al_0.1)_1.95 alloys (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that the magnetization and magnetostriction of the homogenized Tb_0.3Dy_0.7−xPr_x(Fe_0.9Al_0.1)_1.95 alloys decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2, but the spontaneous magnetostriction λ₁₁₁ increases approximately linearly with increasing x. Moreover, the magnetostriction exhibits slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H, showing that a small amount of Pr substitution is beneficial to a decrease in the magnetocrystalline anisotropy. The analysis of the Mössbauer spectra indicated that the easy magnetization direction in the {1 1 0} plane deviates slightly from the main axis of symmetry with Pr concentration x, namely spin reorientation. Comparing with the Al substitution, the effect of Pr substitution for Dy on the spin reorientation is smaller.     

Magnetic and Microwave Absorbing Properties of Electrospun Ba(1−x)LaxFe12O19 Nanofibers

Ba_(1−x)La_xFe₁₂O₁₉ (0.00≤x≤0.10) nanofibers were fabricated via the electrospinning technique followed by heat treatment at different temperatures for 2 h. Various characterization methods including scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and microwave vector network analyzer were employed to investigate the morphologies, crystalline phases, magnetic properties, and complex electromagnetic parameters of nanofibers. The SEM images indicate that samples with various values of x are of a continuous fiber-like morphology with an average diameter of 110±20 nm. The XRD patterns show that the main phase is M-type barium hexaferrite without other impurity phases when calcined at 1100 °C. The VSM results show that coercive force (H_c) decreases first and then increases, while saturation magnetization (M_s) reveals an increase at first and then decreases with La³⁺ ions content increase. Both the magnetic and dielectric losses are significantly enhanced by partial substitution of La³⁺ for Ba²⁺ in the M-type barium hexaferrites. The microwave absorption performance of Ba_0.95La_0.05Fe₁₂O₁₉ nanofibers gets significant improvement: The bandwidth below −10 dB expands from 0 GHz to 12.6 GHz, and the peak value of reflection loss decreases from −9.65 dB to −23.02 dB with the layer thickness of 2.0 mm.     

Study of Zn1−xCoxO (0.02≤x≤0.08) dilute magnetic semiconductor prepared by mechanosynthesis route

Single-phase Zn_1−xCo_xO (0.02≤x≤0.08) dilute magnetic semiconductor is prepared by mechanical milling process. The shift of XRD peaks towards the higher angle and a redshift in the band gap compared to the undoped ZnO ensure the incorporation of Co²⁺ ions in the semiconductor host lattice. Pure Zn_xCo_1−xO phases show the paramagnetic behavior in the temperature range 80 K≤T≤300 K. The room temperature volume magnetic susceptibility (χ_v) estimated in case of Zn_0.96Co_0.04O is ∼10⁻⁵ emu/Oe cm³. The temperature dependence of susceptibility χ_v can be fitted well with Curie law confirming the paramagnetic interaction. The observed crystal-field splitting of 3d levels of Co²⁺ ions inside Zn_1−xCo_xO has been successfully interpreted using Curie law.     

Magnetic/structural diagram, chemical composition-dependent magnetocaloric effect in self-doped antipervoskite compounds Sn1−xCMn3+x (0≤x≤0.40)

The effects of Mn substitutions on the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of antiperovskite Sn_1−xCMn_3+x (0≤x≤0.40) have been investigated detailedly. Both the Curie temperature (T_C) and the magnetizations at 40 kOe decrease with increasing x firstly for x≤0.10, and then increase with increasing x further. The type of magnetic transition changes from first-order to second-order around x=0.10 with increasing x. Chemical composition-dependent MCE is also studied around T_C. With increasing x, the maximal magnetic entropy changes decrease and the magnetic phase transitions broaden. Accordingly, the relative cooling power (RCP) increases with increasing x, reaching the largest values of ∼0.56 J/cm³ (∼75 J/kg) and ∼1.66 J/cm³ (∼221 J/kg) with the magnetic changes of 20 kOe and 48 kOe, respectively. Considering the large RCP, inexpensive, and innoxious raw materials, these serial samples Sn_1−xCMn_3+x are suggested to be potential room-temperature magnetic refrigerant materials.     

The magnetostriction of Fe-(18−x) at% Ga-x at% Al (3≤x≤13.5) alloys

The ingot of Fe-(18−x) at% Ga-x at% Al (3≤x≤13.5) alloys was prepared from high purity elements using a high vacuum arc melting system. The X-ray diffraction patterns indicated that the alloys were disordered bcc A2 structure. The magnetostriction of the alloys was measured and the effect of partial substitution of Ga with Al on the magnetostriction of the alloys was investigated. Fe-9 at% Ga-9 at% Al alloy, the optimizing magnetostrictive alloy was found in Fe-(18−x) at% Ga-x at% Al (3≤x≤13.5) alloys. The saturated magnetostriction of the directional solidification Fe-9 at% Ga-9 at% Al rod is up to 135 ppm for 0 MPa and 221 ppm for 53 MPa. It was found that the alloy has the high linearity of the magnetostriction curve, the low hysteresis and saturated magnetic field, which suggests the directional solidification Fe-9 at% Ga-9 at% Al alloy is a potential candidate for magnetostrictive actuator and transducer applications.     

Influence of Sm-substitution on structure and electromagnetic properties of Ba3−xSmxCo2Fe24O41 powders

Sm-substituted barium hexaferrites, Ba_3−xSm_xCo₂Fe₂₄O₄₁ (x=0-0.25), were prepared by a conventional ceramic sintering method. The microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using powder X-ray diffraction, field emission scanning electron microscopy, vector network analyzer and vibrating sample magnetometry. The results reveal that by introducing a relatively small amount of Sm³⁺ instead of Ba²⁺ an important modification of both structure and high-frequency electromagnetic properties can be obtained. Doping of Sm³⁺ suppressed the grain growth and gave rise to a decrease of the grain size. As the Sm content increases, the static magnetic properties continuously increase. The real part and imaginary part of complex permittivity initially increase with Sm content, and then decreases when x>0.10. The imaginary part of complex permeability decreases after Sm³⁺ is doped. There is no obvious change in the real part of the complex permeability for different Sm contents. The reasons are discussed using electromagnetic theory.     

Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0≤x≤1.0) alloys at low temperature

The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized Pr_xNd_1-xFe_1.9 (0≤x≤1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu₂-type structure. The initial magnetization curve reveals that Pr_0.2Nd_0.8Fe_1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr_0.2Nd_0.8Fe_1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the Pr_xNd_1-xFe_1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ_||) at the field of 5 kOe shows that the substitution of Nd reduces the K₁ remarkably, and the values of λ_|| of Pr_0.2Nd_0.8Fe_1.9 and Pr_0.8Nd_0.2Fe_1.9 alloys are nearly five times larger than that of PrFe_1.9 alloy below 50 K; the λ_|| of Pr_0.8Nd_0.2Fe_1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.     

Magnetic and magnetoelastic properties of Zn-doped cobalt-ferrites—CoFe2−xZnxO4 (x=0, 0.1, 0.2, and 0.3)

Cobalt-ferrite (CoFe₂O₄) based materials are suitable candidates for magnetomechanical sensor applications owing to a strong sensitivity of their magnetostriction to an applied magnetic field. Zn-doped cobalt-ferrites, with nominal compositions CoFe_2−xZn_xO₄ (x=0–0.3), were synthesized by auto-combustion technique using Co- , Fe- , and Zn-nitrate as precursors. X-ray spectra analysis and Transmission electron microscopy studies revealed that the as-prepared powders were comprised of nano-crystalline (∼25–30 nm) cubic-spinel phase with irregularly-shaped grains morphology along with minor impurity phases. Calcination (800 °C for 3 h) of the precursor followed by sintering (1300 °C for 12 h) resulted in a single phase cubic-spinel structure with average grain size ∼2–4 μm, as revealed from scanning electron micrographs. The magnitude of coercive field decreases from ∼540 Oe for x=0 to 105 Oe for x=0.30. Saturation magnetization initially increases and peaks to ∼87 emu/g for x=0.2 and then decreases. The peak value of magnetostriction monotonically decreases with increasing Zn content in the range 0.0–0.3; however the piezomagnetic coefficient (dλ/dH) reaches a maximum value of 105×10⁻⁹ Oe⁻¹ for x=0.1. The observed variation in piezomagnetic coefficient in the Zn substituted cobalt ferrite is related to the reduced anisotropy of the system. The Zn-doped cobalt-ferrite (x=0.1) having high strain derivative could be a potential material for stress sensor application.     

Coexistence of superconductivity and magnetism in the La0.87−xLnxSr0.13FeAsO (Ln=Sm, Gd, Dy) system

The interplay between the superconducting phase and spin density wave order phase was studied. We report the magnetic and superconducting properties of the hole-doped FeAs-based superconducting compound La_0.87−xLn_xSr_0.13FeAsO (Ln=Sm, Gd, Dy; 0≤x≤0.06). Both resistivity and magnetic susceptibility measurements show that the superconducting transition temperature decreases with increase in composition of magnetic ions. The hysteresis loop of the La_0.87−xLn_xSr_0.13FeAsO sample shows a superconducting hysteresis in addition to a paramagnetic background. The experiment demonstrates that the magnetism and superconductivity coexist in hole-doped FeAs-based superconducting compounds. Among these three magnetic rare-earth elements, the influence of Dy³⁺ doping on superconductivity is more evident than that of Gd³⁺ doping, while the influence of Sm³⁺ doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis.