立方结构Fe基磁性材料弹性系数第一性原理计算

通过赝势平面波法(CASTEP)及全电势线性缀加平面波法(FLAPW)，以bcc-Fe为对象，研究第一性原理计算立方结构Fe基磁性材料弹性系数的方法，分析影响计算立方结构Fe基磁性材料弹性系数准确度的各项因素. 结果表明，在第一性原理弹性系数计算中，晶格常数是决定弹性系数计算准确度的关键因素；势函数的选择也会影响计算准确度. 使用全电势基矢的FLAPW法可以得到更为精准的弹性系数计算结果. 计算得到bcc-Fe的弹性系数C₁₁，C₁₂，C₄₄分别为246 GPa，121 GPa，113 GPa，与实验值基本一致. 利用本方法，计算了新型Fe-Ga磁致伸缩材料的弹性系数C₁₁，C₁₂，C₄₄分别为207 GPa，166 GPa及108 GPa. 关键词： 弹性系数 磁致伸缩材料 赝势平面波法 全电势线性缀加平面波法     

铁镓单晶Janus-Helmholtz换能器

针对深水、低频、宽带换能器的技术需求,结合Janus-Helmholtz换能器的结构特点和铁镓单晶材料低场应变大及机械强度高的特性,提出了铁镓单晶Janus-Helmholtz换能器设计方案。采用永磁偏磁场和环形闭合磁路,建立了一系列铁镓单晶磁致伸缩换能器理论分析模型,包括对磁致伸缩材料参数进行线性化处理,设计了换能器最佳工作点,结合静态磁场和动态磁场分布情况分段细化换能器驱动等效参数,以及利用全阻抗模型通过电感损耗等效计算换能器静态阻抗,然后通过二维有限元分析等效模型,优化分析了换能器的结构参数与电声性能。最后制作了换能器样机,并进行了测试与分析。对比仿真和测试结果表明:全阻抗模型得到的阻抗曲线与样机测试结果相一致,有限元等效模型计算的发送电流响应与样机测试结果良好吻合。换能器样机水中谐振基频为1000 Hz,谐振频率下发送电流响应176.4 dB;在875～2300 Hz频率范围内,发送电流响应起伏不大于6 dB;增加驱动电流有效值到16.2 A,最大声源级可以达到196.2 dB。     

A method based on magnetic moment measurement to identify the structural transition of quenched Fe1 -xGax (x = 0.15ben 0.30) alloys

A method based on the measurement of Fe average atomic magnetic moment to identify the structural transition caused by the increase of Ga content in quenched Fe_{1 - x}Ga_x alloys (0.15 ≤ x ≤ 0.30) is proposed. The quenched Fe_{1 - x}Ga_x alloys show a change of the Fe average atomic magnetic moment from 2.25 μ_B to 1.78 μ_B and then to 1.58 μ_B, which corresponds to the structural transition from A2 to D0₃ and then to B2. The relationship between the structure and the magnetostriction is clarified, and the maximum magnetostriction appears in the A2 phase. The variation tendency of the magnetostriction is well characterized, which also reflects the structural transition.     

Magnetostructural transition in NiCuCoMnGa alloys

The effects of the addition of Co on the martensitic transformation and Curie transition temperatures of polycrystalline Ni46-xCu4CoxMn33.sGa16.5 （x = 0, 1, 3, 5） alloys are investigated. An abrupt decrease in the martensitic transformation temperature and an obvious increase in the Curie transition temperature of austenite （TA） are observed when Co is doped in the NiCuMnGa alloy. As a result, the composition range for obtaining the magnetostructural transition is extended. Furthermore, the effect of a strong magnetic field on the magnetostructural transition is analyzed. This study offers a possible method to extend the composition range for obtaining magnetostructural transition in Heusler alloys.     

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.     

Relation between oxidation microstructure and the maximum energy product loss of a Sm2Co17 magnet oxidized at 500 ℃

The oxidation microstructure and maximum energy product (BH)_max loss of a Sm(Co_0.76, Fe_0.1, Cu_0.1, Zr_0.04)₇ magnet oxidized at 500 ℃ were systematically investigated. Three different oxidation regions were formed in the oxidized magnet: a continuous external oxide scale, an internal reaction layer, and a diffusion zone. Both room-temperature and high-temperature (BH)_max losses exhibited the same parabolic increase with oxidation time. An oxygen diffusion model was proposed to simulate the dependence of (BH)_max loss on oxidation time. It is found that the external oxide scale has little effect on the (BH)_max loss, and both the internal reaction layer and diffusion zone result in the (BH)_max loss. Moreover, the diffusion zone leads to more (BH)_max loss than the internal reaction layer. The values of the oxidation rate constant k for internal reaction layer and oxygen diffusion coefficient D for diffusion zone were obtained, which are about 1.91 × 10^-10 cm²/s and 6.54 × 10^-11 cm²/s, respectively.     

First principles study on the magnetocrystalline anisotropy of Fe--Ga magnetostrictive alloys

This paper investigates the electronic structure and magnetocrystalline anisotropy of Fe--Ga magnetostrictive material by means of the full potential-linearized augmented plane-wave method within the generalized gradient approximation. The 3d-orbit splitting of Fe atoms in D0₃, B2-like and L1₂ crystalline structures of Fe--Ga is calculated with consideration of the crystal field as well as the spin--orbit coupling effect. Because of the frozen orbital angular momenta of the 3d-orbit for Fe atoms in Fe--Ga magnetostrictive alloys and the spin--orbit coupling, the distribution of the electron cloud is not isotropic, which leads to the anisotropy of exchange interaction between the different atoms. A method on estimating the magnetocrystalline anisotropy of Fe--Ga alloys by means of calculating orbit-projected density of states for Fe atoms is performed. The anisotropic distribution of the electron cloud of Fe atoms in these three crystalline structures of Fe--Ga is studied based on the above method showing the highest magnetic anisotropy for B2-like structure. This qualitative method comes closer to physical reality with a vivid physical view, which can evaluate the anisotropy of electron cloud for 3d transition atoms directly. The calculated results are in good agreement with both the previous theoretical computation and the tested value on the magnetic anisotropy constant, which confirms that the electron cloud anisotropy of Fe atoms could well characterize the magnetocrystalline anisotropy of Fe--Ga magnetostrictive material.     

N i50.5Mn24Ga25.5取向晶体相变应变性能的研究

采用区熔法制备了Ni505_50.5Mn24₂₄Ga255_25.5取向晶体，在底部、中部和顶部各切取一块样品进行相变应变测试.在中部样品中获得了高达14%的相变应变，应变随加热冷却循环次数的增加而逐步降低，第9次和第10次相变时应变为08%.在底部和顶部样品中，降温过程的应变随温度的变化呈现先收缩后膨胀或先膨胀后收缩的现象，我们认为这是由于样品中高度择优取向的马氏体变体竞争的结果所致. 关键词： NiMnGa 取向晶体 相变应变     

Sm(CobalFe0.1Cu0.1Zr0.033)6.9高温永磁合金的矫顽力

对Sm(Co_balFe_0.1Cu_0.1Zr_0.033)_6.9合金, 经810℃等温时效后以0.5℃/min逐渐冷却, 在600℃-400℃温度区间淬火, 研究了不同淬火温度下的磁滞回线、磁畴和矫顽力温度系数β. 发现时效600℃淬火后磁滞回线出现台阶状, 说明畴壁中应存在两处钉扎. 随淬火温度的降低, 合金的室温矫顽力显著增加, 磁滞回线的台阶消失. 通过磁畴形貌发现时效600℃淬火后的磁畴接近条形畴, 1:5相中Cu分布相对均匀, 形成的畴壁钉扎较弱, 从而使磁滞回线出现台阶, 决定矫顽力的畴壁钉扎位于两相界面处; 随时效淬火温度的降低, 磁畴逐渐细化, 畴壁1:5相中的畴壁能降低, 形成了较强的内禀钉扎, 并决定材料的矫顽力, 两相界面处的畴壁钉扎被掩盖. 对不同温度淬火合金的高温矫顽力研究表明, 最强的畴壁钉扎位于两相界面处时, 矫顽力随温度升高逐渐增加, 矫顽力出现温度反常现象; 最强的畴壁钉扎位于1:5相中心时, 矫顽力随温度升高逐渐衰减. 当测试温度达到500℃后不同淬火温度样品的矫顽力几乎相同, 此时最强畴壁钉扎均在两相界面处.     

Martensitic transformation in Cu-doped NiMnGa magnetic shape memory alloys

This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L2₁ cubic austenite by Cu substituting for Ni in the Ni_50-xCu_xMn₃₁Ga₁₉ (x=2--10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (k_F) is applied to evaluate the change of the martensitic transformation temperature. The increase of k_F leads to the increase of the martensitic transformation temperature.