Magnetostriction of Fe81Ga19 oriented crystals

The effect of the orientation on the magnetostriction in Fe 81 Ga 19 alloy has been investigated experimentally and theoretically.The Fe 81 Ga 19 [001] and [110] oriented crystals were prepared and the magnetostriction was measured under different pre-stress.The saturation magnetostriction of the [001] oriented crystal increases from 170×10-6 to 330×10-6 under the pre-stress from 0 to 50 MPa.The [110] oriented crystal has a saturation magnetostriction from 20×10-6 to 140×10-6 with the compressive pre-stress from 0 to 40 MPa.The magnetostriction of [001] and [110] oriented crystals has been simulated based on the phenomenological theory.The domain rotation path has been determined and the resultant magnetostriction calculated under different pre-stress.The experimental and simulated results both show that the [001] oriented crystal exhibits better magnetostriction than [110] oriented crystal.The enhancement of the saturation magnetostriction by the compressive pre-stress in the [110] oriented crystal is higher than that in the [001] oriented crystal.     

Magnetoelastic properties of Nd6Fe13Cu intermetallic compound

Magnetoelastic properties of Nd₆Fe₁₃Cu intermetallic compound are reported. To study the magnetoelastic behaviour of this compound, the thermal expansion as well as the longitudinal (λ_l) and transverse (λ_t) magnetostriction were measured by using the strain gauge method in the selected temperature range of 80-500 K under applied magnetic fields up to 1.5 T. An anomaly and invar-type effects are observed in the linear thermal expansion and α(T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic-paramagnetic transition occurs. In the low field region, the absolute values of the anisotropic magnetostriction are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.     

Elastic Modulus of Fe72.5Ga27.5 Magnetostrictive Alloy

The elastic modulus of Fe72.5Ga27.5 magnetostrictive alloy is determined by testing ac impedance resonance frequency and first-principle calculations. The observed elastic modulus is 90.2 GPa for a directionally solidified sample and 103.4 GPa for a water-quenched sample tested in a dc magnetic field of 32. 7mT without compressive pre-stress. The bulk modulus by first-principles calculation is 179.3GPa which is basically consistent with the experimental result. The elastic modulus first increases and then decreases with increasing dc magnetic field, attributed to magnetostriction occurrence in the Fe72.5Ga27.5 alloy. The elastic modulus increases with increasing compressive pre-stress, resulting from the initial magnetic states change under the applied compressive pre-stress. The elastic modulus increases match well with the improved magnetostriction after quenching.     

Magnetostriction relative to pretransition in Ni50.5Mn24.5Ga25 single crystal

The strain behaviors as well as the structural and magnetic changes relative to the pretransition in the Ni_50.5Mn_24.5Ga₂₅ single crystals have been characterized by various methods, such as pretransition strain, magnetostriction, magnetization measurements, and TEM observations. A large magnetostriction up to 505 ppm measured in the [001] direction of the sample is obtained at the pretransition temperature with only a low magnetic field of about 1 kOe applied along the [010] direction. We found that not only the pretransition strain pronounces a more large change, but also the magnetostriction at a certain temperature exhibits a more large magnitude for field applied along the [010] direction than with field along the [001] direction. It is concluded that the magnetoelastic interaction is responsible for the premartensitic transition, and the magnetoelastic interaction in the [010] direction is stronger than that in the [001] direction.     

Magnetoelastic properties of ErMn6Sn6 intermetallic compound

The thermal expansion and magnetostriction of polycrystalline sample of the ErMn₆Sn₆ intermetallic compound with hexagonal HfFe₆Ge₆-type structure are investigated in the temperature range of 77 K to above 400 K. The thermal expansion measurement of the sample shows anomalous behavior around its T_N=340 K. The isofield curves of volume magnetostriction also reveal anomalies at paramagnetic-antiferromagnetic and antiferromagnetic-ferrimagnetic phase transitions. In the antiferromagnetic state, the transition to ferrimagnetism can be induced by an applied magnetic field. The threshold field for the metamagnetic transition H_th increases from 0.18 T at 84 K to about 1 T around 220 K, and then decreases monotonously to T_N. This behavior is well consistent with that observed earlier on magnetization curves attributed to exchange-related metamagnetic transition rather than the anisotropy-related one. Furthermore, the low H_th values suggest that the Mn-Mn coupling in ErMn₆Sn₆ is not so strong. The experimental results obtained are discussed in the framework of two-magnetic sublattice by bearing in mind the lattice parameter dependence of the interlayer Mn-Mn exchange interaction in this layered compound. From the temperature dependence of magnetostriction values and considering the magnetostriction relation of a hexagonal structure, we attempt to determine the signs of some of the magnetostriction constants for this compound.     

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.     

Irreversible magnetovolume effect in Nd7Rh3 single crystal

Magnetovolume effect in Nd₇Rh₃ single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2 K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.     

Modification of the saturation magnetostriction constant after thermal treatments for the Co58Fe5Ni10B16Si11 amorphous ribbon

A new method for measuring the magnetostriction constant has been developed. The resolution of this sensitive method allows to measure values of that constant as low as 10^-9. It has been found that after thermal treatments, the magnetostriction constant of the amorphous ribbon whose nominal composition is Co₅₈Fe₅Ni₁₀B₁₆Si₁₁ changes not only its absolute value but also its sign. The kinetics of this variation has also been studied and a mean value of the activation energy of 0.8 eV for the relaxation process was obtained. Such variations of the magnetostriction constant are discussed as produced by modifications of the short-range order during annealing.     

Study of the magnetostrictive strains in Pr6Fe11Ga3 alloy

Magnetoelastic properties of the Pr₆Fe₁₁Ga₃ alloy are studied by magnetostriction and thermal expansion measurements. The effects of short- and long-range magnetic ordering processes about Curie temperature clearly appear in the temperature dependence of the spontaneous magnetostriction as two increasing steps with decreasing temperatures. Thermal variations of the total magnetocrystalline anisotropy introduce pronounce changes in the isofield curves of the forced magnetostriction as a negative minimum below 200 K, a compensation phenomena about 250 K, and a positive maximum between 250 K and T_c=320 K. The observed behavior of magnetostriction is discussed in terms of the competitive anisotropies of Pr and Fe sublattices and coupling magnetostrictive constants.     

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.     

Magnetostriction and anisotropy of CoxFe3xO4 (x≤0.1) single crystals

Using the strain gauge technique, the magnetostriction constants λ_[100] and λ_[111] have been measured on single crystals of Co_xFe_3-xO₄ with compositions 0.0005≤x≤0.1 in the temperature range between 100 and 300 K and using magnetic fields up to 23 kOe. The presence of Co²⁺-ions gives rise to a very large negative value of λ_[100] and a fairly large positive value of λ_[111]. A linear relationship is found between the magnetostriction constants and the cobalt concentration.Some conclusions about the anisotropic beheviour of the samples can be made, based on the magnetostriction measurements. The change of the direction of easy magnetization from [111] to [100] in the temperature range just above the Verwey transition, is illustrated and discussed. It turned out to be possible to determine an effective anisotropy constant K'₁ through a curve fitting procedure. It is found that 1n K'₁ varies linearly with T.     

TbyDy1-y(Fe1-xTx)2(T=Al,Mn)的磁致伸缩与内禀磁致伸缩特性

用直拉单晶生长系统制备Tb_yDy_1-x(Fe_1-xT_x)₂(T=Al,Mn)单晶,并测量其磁致伸缩.用电弧炉合成多晶Tb_yDy_1-y(Fe_1-xT_x)₂(T=Al,Mn),并用X射线衍射方法测量拟合得到内禀磁致伸缩.结果表明,Al和Mn替代后饱和磁场降低,说明Al和Mn的替代明显地降低了各向异性能.随Al和Mn替代量的增加,总的趋势是材料的内禀磁致伸缩λ₁₁₁降低.对Tb_0.5Dy_0.5(Fe_0.9Mn_0.1)₂单晶,在不加压情况下的磁致伸缩效果并不明显,但当施加压力时,磁致伸缩变化显著,尤其在12—26MPa压力下,磁致伸缩变化很大,且低场效果很好. 关键词：     

稀土掺杂La-Sr-Mn-O的室温磁致伸缩效应

采用两种不同的方法制备了不同稀土含量的(La_1-xR_x)_2/3Sr_1/3MnO₃(R=Sm,Tb)大块多晶样品,并研究了它们的晶体结构及室温下的磁致伸缩效应.分析表明,随Sm,Tb对La的替代,样品的晶体结构从菱面体相转变为正交相.在结构相转变点附近,样品在室温下的磁致伸缩效应出现极大值.样品在室温下的磁致伸缩主要来源于材料中的交换磁致伸缩. 关键词：     

Structural,electronic and magnetic properties of hydrogenated BC2N

Density functional theory has been used to study the electronic and magnetic properties as well as the stability on the hydrogenated BC₂N sheets. It is found that two different structures (BC₂NH-I and BC₂NH-II) with the ferromagnetic ground states can be formed when removing the H atoms from one side of semi-hydrogenated BC₂N sheet. By applying tensile strain, both of their magnetisms are robust to 2.0 μ_B. However, the magnetisms are sensitively changed by compressive strain larger than ?6%. The BC₂NH-I system can be transitioned from semiconductor to half-metal and then to metal when the compressive strain is changed from ?6% to ?8%. And the BC₂NH-II system can be changed into half-metal by applying the compressive strain between ?6% and ?7.5%. Our calculation results suggest a possible way to tune the electronic and magnetic properties by choosing the appropriate structural type and the external strain, which would have potential applications in spintronics and nanodevices.     

Thermal expansion and magnetostriction of GdAg2, and relations to the magnetoelastic paradox

The antiferromagnet GdAg₂ has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi₂B₂C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM).     

Invar effects in Zr0.7Nb0.3Fe2

A thermal expansion anomaly similar to that of the invar alloy was observed in a Laves phase intermetallic compound, Zr_0.7Nb_0.3Fe₂. This anomaly is explained as a result of a large spontaneous volume magnetostriction. Magnetic properties and magnetovolume effects of this material are discussed on the basis of the band of ferromagnetism.     

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.     

Tb0.3Dy0.7Fe2单晶中巨磁致伸缩的逆效应

研究了Terfenol-D材料中巨磁致伸缩的逆效应,即磁机械效应.基于Stoner-Wohlfarth(SW)模型,考虑磁晶各向异性和应力各向异性能,依据自由能极小原理,获得了退磁态下Terfenol-D单晶中磁化强度方向和压应力的关系.采用数值方法求解了平衡条件下的非线性方程组.理论结果表明,Terfenol-D巨磁致伸缩单晶中的磁各向异性取决于磁晶各向异性和应力各向异性之间的竞争.在压应力的作用下,Terfenol-D单晶中的磁各向异性由立方向单轴转变.理论和实验结果的比较表明,存在一个临界压应力,使磁致伸缩效应达到极大值.该理论结果还解释了压应力使得Terfenol-D单晶材料难于磁化和磁致伸缩效应出现极大值的实验事实.理论计算不仅为研究这类问题提供了一个更准确的方法,而且其结果也有助于理解类似材料中的磁化过程.     

Field and temperature induced colossal strain in Gd5(SixGe1−x)4

Gd₅(Si_xGe_1−x)₄, known for its giant magnetocaloric effect, also exhibits a colossal strain of the order of 10,000 ppm for a single crystal near its coupled first-order magnetic-structural phase transition, which occurs near room temperature for the compositions 0.41≤x≤0.575. Such colossal strain can be utilised for both magnetic sensor and actuator applications. In this study, various measurements have been carried out on strain as a function of magnetic field strength and as a function of temperature on single crystal Gd₅Si₂Ge₂ (x=0.5), and polycrystalline Gd₅Si_1.95Ge_2.05 (x=0.487) and Gd₅Si_2.09Ge_1.91 (x=0.52). Additionally a giant magnetostriction/thermally induced strain of the order of 1800 ppm in polycrystalline Gd₅Si_2.09Ge_1.91 was observed at its first order phase transition on varying temperature using a Peltier cell without the use of bulky equipment such as cryostat or superconducting magnet.     

A structural, magnetostrictive and M?ssbauer study of Tb0.3Dy0.7(Fe0.9 T 0.1)1.95 alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys is the MgCu₂-type cubic Laves phase structure for different substitution. The magnetostriction λ{ins} decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λ{ins}. It was also found that the effect of different substitutions on the spontaneous magnetostriction λ{in111} is distinct. The analysis of the M?ssbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.