Magnetostriction and structural characterization of Fe-Ga bulk alloy prepared by copper mold casting

Rapidly solidified Fe100-xGax （x=16-20） alloy rods were prepared by induction melting and copper mold casting under the protection of inert gases. The optical microscopy observation shows that the large and elongated columnar grains grow along the radial direction, which is parallel to the temperature gradient direction. The preferred orientation texture along the axial direction of the rod was detected by XRD. With the increase of Ga content, the saturation magnetization （Ms） of the alloys decreases distinctly and the dynamic response in low magnetic field increases drastically, the maximum longitudinal saturation magnetostriction for as-cast Fe82Ga18 alloy rods is 92×10-6 under an applied magnetic field strength of 30 kA/m. The large magnetostriction of Fe100-xGax alloys is attributed to the rapidly solidified disordered A2 phase and the high concentration of short range order of Ga atom clusters, which are arranged in the direction and finally trigger the formation of modified-DO3 structure, just as shown by the split of the （200） diffraction peak. Ordered DO3 phase is not conducive to the magnetostriction.

Magnetostriction and microstructure of melt-spun Fe_(77)Ga_(23) ribbons prepared with different wheel velocities

A set of stacked ribbons with the composition of Fe77Ga23 were prepared with different wheel velocities of 7 m/s, 12.5 m/s and 25 m/s（named as S7, S12.5 and S25, respectively）. High resolution X-ray diffraction patterns of these ribbons show that all the ribbons present the disordered A2 structure, whereas an additional modified-DO3 phase is detected in S12.5 and S25. S25 has stronger（100） texture than other two samples. Ga K-edge extended X-ray absorption fine structure results indicate that both bond distance and the number of Ga atoms in the second neighbor shell around Ga decrease with increasing wheel velocity. No Ga cluster is detected in the studied ribbons. A short-range ordering Ga-rich phase and large local strain have no obvious influence on magnetostriction of S7. It is believed that both the（100） texture and the additional modified-DO3 phase play a positive role in magnetostrictive properties of Fe77Ga23 ribbons.

INFLUENCE OF HEAT TREATMENT ON THE COMPRESSIVE STRESS EFFECT OF MAGNETOSTRICTION OF <112> AXIAL ALIGNED Tb-Dy-Fe ALLOYS

The magnetostrictive properties of <112> axial aligned Tb0.3Dy0.7(Fe1-xMx)1.95(M=Mn, Al, x=0～ 0.15) alloys prepared by directional solidification are reported. The influence of heat treatment on microstructure and the compressive stress effect of magnetostriction is discussed.

THE EFFECT STRESS ON THE MAGNETOSTRICTION IN TWIN- FREE SINGLE CRYSTALS Tb_y Dy_(1-y) (Fe_(1-x) T_x)_2 (T=Al,Mn)

Magnetostriction at room temperature under various conditions of compressive prestress and applied fields in Tb yDy 1-y (Fe 1-x T x) 2 (T=Al,Mn) twin-free single crystals were investigated. The substitution of Al or Mn for Fe lowers the magnetostriction un-der ordinary temperature and pressure, but it also decreases the saturation field, which enables these materials with potential benefits for applications.

Fabrication,magnetostriction properties and applications of Tb-Dy-Fe alloys:a review

As an excellent giant-magnetostrictive material, Tb-Dy-Fe alloys(based on Tb0.27-0.30Dy0.73-0.70Fe1.9-2Laves compound) can be applied in many engineering fields, such as sonar transducer systems, sensors, and micro-actuators. However, the cost of the rare earth elements Tb and Dy is too high to be widely applied for the materials. Nowadays, there are two different ways to substitute for these alloying elements. One is to partially replace Tb or Dy by cheaper rare earth elements, such as Pr, Nd, Sm and Ho; and the other is to use non-rare earth elements, such as Co, Al, Mn, Si, Ce, B, Be and C, to substitute Fe to form single MgCu_2-type Laves phase and a certain amount of Re-rich phase, which can reduce the brittleness and improve the corrosion resistance of the alloy. This paper systemically introduces the development, the fabrication methods and the corresponding preferred growth directions of Tb-Dy-Fe alloys. In addition, the effects of alloying elements and heat treatment on magnetostrictive and mechanical properties of Tb-Dy-Fe alloys are also reviewed, respectively. Finally, some possible applications of Tb-Dy-Fe alloys are presented.

Effect of fabrication parameters on the microstructure,in-plane anisotropy and magnetostriction of Fe-Ga thin films

The microstructure,in-plane anisotropy,and magnetic properties of Fe-Ga thin films were investigated by X-ray diffraction analysis,vibrating sample magnetometer,and capacitive cantilever method.The in-plane induced anisotropy is well formed by the applied magnetic field during sputtering,and the anisotropy field Hk decreases with the sputtering power increasing.The coercivity of Fe-Ga thin films decreases with increasing power when the sputtering power is less than 60 W and increases when the power is larger than 60 W.The magnetostriction of the thin films reaches 66 × 10-6 at the sputtering power of 60 W.Excellent Fe-Ga films,which exhibit good field sensitivity,low coercivity and high magnetostriction,have been fabricated at the power of 60 W,and they can be used as the materials of magnetostrictive transducers.

Influence of Al on the magnetostriction of Fe-Ga polycrystal alloys under compressive stress

Fe80Ga20-xAlx （x = 0, 6, 9, 14） ingots were prepared from high purity elements using a vacuum induction system. X-ray diffraction patterns show that the alloys are A2 disordered structures. The influence of the partial substitution of Ga in Fe-Ga alloys with A1 on their magnetostrictive properties was investigated, and the effects of different heat treatment conditions on the magnetostriction and microstructure of the alloy rods were also examined. The saturation magnetostriction value of FesoGa2o can reach to 240 x 10-6 under a compressive stress of 20 MPa. The Fe80GallA19 alloy has many good properties, such as low hysteresis, high linearity of the magnetostriction curve, and low saturated magnetic field, which make it a potential candidate for magnetostrictive actuator and transducer applications. It is found that subgrains have little influence on the magnetostriction of Fe-Ga alloys.

Structure and magnetic properties of mechanically alloyed Tb_(0.2)Pr_(0.8)(Fe_(0.4)Co_(0.6))_(1.93) and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb0.2Pr0.8（Fe0.4Co0.6）1.93 was synthesized by mechanical alloying （MA） and subsequent annealing process. The structure and magnetic properties of Tb0.2Pr0.8（Fe0.4Co0.6）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 Tb0.2Pr0.8（Fe0.4Co0.6）1.93 alloy with the single phase of MgCu2-type structure can be successfully synthesized by MA method. The sample annealed at 450℃ is found to have a coercivity of 196 kA/m at room temperature. An epoxy/Tb0.2Pr0.8（Fe0.4Co0.6）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 Tb0.2Pr0.8（Fe0.4Co0.6）1.93 composite combines a high magnetostriction with a significant coercivitv, which is a oromising magnetostrictive material.

Bonded Terfenol-D composites with low eddy current loss and high magnetostriction

Bonded Terfenol-D composites,with high electrical resistivity and low eddy current loss,can be used in an alternating magnetic field with high frequency.However,the nonmagnetic binder impairs the magnetostriction of the composites.To achieve high magnetostriction and low eddy current loss,the mixture of the alloy powder and binder was compressed at low pressure in an oriented magnetic field.After this,the aligned samples were recompressed by cold isostatic pressing（CIP）.Besides,the effect of particle size on the magnetostriction of the bonded Terfenol-D composites was also studied.The results showed that the bonded Terfenol-D composites had excellent magnetostriction when the particle size was 50-80 μm.The oriented magnetic field and CIP could improve the magnetostriction of the bonded composites,which reaches 1020×10-6.The bonded Terfenol-D composites had good compact structure and high density（7.24 g/cm3）.The magnetic loss of the bonded Terfenol-D composites was 192 mW/cm3 at a frequency of 100 kHz in a magnetic field of 960 A/m,which was about one third of that of casting Terfenol-D alloys.

Structure and magnetostriction of Tb_(0.4)Nd_(0.6)(Fe_(0.8)Co_(0.2))_(1.90) alloy prepared by solid-state synthesis

Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Nd-containing magnetostrictive Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy. The structure, thermal stability and phase transformation were investigated as functions of composition, milling process and annealing temperature. An amorphous phase was formed by high-energy ball milling for 5 h with the ball-to-powder weight ratio of 20:1, which crystallized into MgCu2-type and PuNi3-type crystalline structure with different annealing temperatures. The magnetoelastic properties were investigated by means of a standard strain technique. The high Nd-content (Tb,Nd)(Fe,Co)2 Laves phase for the composition Tb0.4Nd0.6(Fe0.8Co0.2)1.90 was synthesized by MA process plus annealing at 500 ℃ for 30 min.

MEASUREMENTAL RESEARCH ON THE MAGNETOMECHANICAL COUPLING PROPERTIES OF RARERARTH GIANT MAGNETOSTRICTION MATERIALS

The physical modelanditsequivalentcircuitoftestapparatusissetup by meansofimpedanceanalysis method. The magnetostriction coefficient, magnetomechanicalcoupling coefficient,frequency and anti- frequency of TbxDy1 - xFe2 - z(0 27 ≤x ≤0 3 ,0 ≤z ≤0 1) rod are measured. Somecoupling problems with mechanicalstress and electromagnetic field such as flux leakage in magnetic path are discussed. The comparing calculated with tested resultsshowsthe accuracyof measurementand thesimplification of model.

Magnetostriction of Pseudobinary Compounds Pr_(0.15)Tb_xDy_(0.85-x)Fe_2(x=0 to 0.85)

The compound ingots of Pr0.15TbxDy0.85-xFe2 (x=0 to 0.85) were prepared by arc melting in a water Cu boat using arc furnace under a purified Ar atmosphere. Appropriate annealing (850℃, 100 h) can obtain single Laves phase compound. The magnetostriction for these systems will rise obviously when partially substituted Tb or Dy by Pr.

Giant Magnetostrictions of Tb-Dy-Fe Polycrystals with < 110 > Axial Alignment

Preparing method and processing of Tb-Dy-Fe alloy samples with [110] axial orientation as well as their magnetostrictive properties have been studied. It has been found that the magnetostrictive strains of polycrystal samples with [110] axial orientation can reach (1550-1900) ×10~-6 in a low magnetic field less than 80 kA/m, which are equal to or somewhat better than that of the polycrystal samples with [112] axial orientation.

Influence of Tb on easy magnetization direction and magnetostriction of PrFe1.9 alloy

The crystal structures, magnetization, and spontaneous magnetostriction of ferromagnetic Laves phase Pr1-xTbxFe1.9 compounds are investigated in a temperature range between 5 K and 300 K. High resolution synchrotron x-ray diffraction(XRD) analysis shows that different proportions of Tb in Pr1-xTbxFe1.9 alloys can result in different easy magnetization directions(EMD) below 70 K, i.e., [100] with x = 0.0, and [111] with x ≥ 0.1. This indicates Tb substitution can lead the EMD to change from [100] to [111] with x rising from 0.0 up to 0.1. The Tb substitution for Pr reduces the saturation magnetization Ms and the magnetostriction to their minimum value when x = 0.6, but it can increase low-field(0 ≤ H ≤9 kOe, the unit 1 Oe = 79.5775 A·m-1) magnetostriction when x = 0.8 and 1.0 at 5 K. This can be attributed to the larger magnetostriction of PrFe1.9 than that of TbFe1.9, as well as the decrease of the resulting anisotropy due to Tb substitution at low temperatures.

Phase Transformation and Magnetostriction of (R-Pr)(Fe-T)_2 (R=Dy Tb; T=Co, Ni)

Structure and magnetostriction of Dy1-Pr_x Fe_2 (0≤x≤0.5), Dy_0.6Pr_0.4(Fe_1-_yT_y)_2 (0≤y≤0.6), and Tb_1-z Pr_z(Fe_0.4Co_0.6)_2 (0≤z≤1.0) alloys (T=Co, Ni) have been investigated. It is found that the matrix of the alloys Dy_1-xPr_xFe_2 is a single phase (Dy, Pr)Fe_2 with MgCu_2-type structure and the second phase is (Dy, Pr)Fe_3 when x≤0.2. The amount of (Dy, Pr)Fe_3 phase increases with increasing Pr content and becomes the main phase when x=0.4. The matrix of Dy1_-x.Pr_xFe_2 is found to be the (Dy, Pr)_2Fe_17 phase with Th_2Zn_17-type structure when x=0.5. It is found that the amount of the cubic Laves phase (Dy, Pr)(Fe, Co)_2 in the Dy_0.6Pr_0.4(Fe_l-Co_y)2 increases with increasing Co concentration when 0≤y≤0.6. The substitution of Ni for Fe is nearly not favorable for the formation of the cubic Laves phase (Dy, Pr)(Fe, Ni)_2 in (Dy_1-xPr_x)Fe_2. The matrix of (Tb_1-z Pr_z)(Fe_0.4Co_0.6)_2 is a (Tb, Pr)(Fe, Co)_2 phase with the MgC_u2-type cubic Laves structure and a second phase of small amount is (Tb. Pr)(Fe, Co)_3 phase when z≤O.2, z=0.5 and 1.0. When 0.2<z≤0.4, the amount of the (Tb, Pr)(Fe, Co)_3 phase with PuNi_3-type structure increases with increasing z and becomes the main phase when z=0.4. When 0.5<z≤0.6 the amount of the (Tb, Pr)(Fe, Co)_3 phase increases sharply, whereas for 0.6<z≤0.8 it decreases with increasing z. The polycrystalline magnetostriction, λ｜｜ - λ｜. at room temperature of Dy_l-xPr_xFe_2 exhibits a peak when x=0.3. The λ｜｜ - λ｜ for Dy_0.6Pr_0.4(Fe_1-y.M_y)_2 (M=Co, Ni) and Tb_l-zPrz(Fe_0.4Co_0.6)_2 is also examined.

Relationship between crystal growth mode, preferred orientation and magnetostriction of (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys

The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of （Tb0.3Dy0.7）Fe1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of （Tb0.3Dy0.7）Fe1.95 alloys. At lower solidification rates, the sample with 〈110〉 preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.

Thermal expansion anomaly and spontaneous magnetostriction of Tb_2Fe_(15)Cr_2 compound

The structural and magnetic properties of Tb2Fe15CF2 compound were investigated by means of X-ray diffraction and magnetization measurements. Tb2Fe15Cr2 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Tb2Fe15Cr2 compound from 372 to 452 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.14×10^-5 K^-1. The magnetostrictive deformations from 292 to 450 K were calculated. The result showed that the spontaneous volume magnetostrictive deformation ms remains nearly constant with increasing temperature up to 360 K, but decreases with the further increase of temperature. The spontaneous linear magnetostrictive deformation λc along the c axis decreases with increasing temperature. The spontaneous linear magnetostrictive deformation, λa, in the basal-plane increases with increasing temperature up to 360 K, but decreases with further increasing temperature.

Magnetostriction Increase of Tb0.3Dy0.7Fe1.95 Alloy Prepared by Solidification in High Magnetic Fields

Tb0.3Dy0.TFe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the （Tb,Dy）Fe2 phase changed from （113） to （111） direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.TFe1.95 alloys is linked to the amount and the crystal orientation behavior of the （Tb,Dy）Fe2 phase.

Spontaneous volume magnetostriction of Dy_2AlFe_(12)Mn_4 compound

The structure and magnetic properties of Dy2AlFe12Mn4 compound have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe12Mn4 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Dy2AlFe12Mn4 compound from 229 to 280 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.8×10^-5 K^-1. The magnetostrictive deformations from 105 to 270 K have been calculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 6.2 × 10^-3 to near zero with the temperature increasing from 105 to 270 K, the spontaneous linear magnetostrictive deformation λc along the c axis is much larger than the spontaneous linear magnetostrictive deformation λa in basal-plane at the same temperature except close to 249 K.

Giant Volume Magnetostriction Caused by Itinerant Electron Metamagnetic Transition and Pronounced Invar Effects in La(Fe_xSi_(1-x))_(13) Compounds

A first-order itinerant electron metamagnetic (IEM) transition above the Curie temperature Tc for ferromagnetic La(Fe_xSi_1-x)13 compounds has been confirmed by applying magnetic field. The volume change just above T_C for x=0.88 is huge of about 1.5%, which is caused by a large magnetic moment induced by the IEM transition. These compounds have a possibility for practical applications as giant magnetostrictive materials. Pronounced Invar effects bring about a negative thermal expansion below TC, closely correlated with the negative mode-mode coupling among spin fluctuations.