This study investigated the phase stability, mechanical properties, electronic band structure and magnetic properties of the half-Heusler alloys FeMnZ (Z = Si, Ge and Sn) by first-principles calculations. The most stable structure for all the alloys is ferrimagnetic Type-I structure where Fe, Mn and Z atoms occupying sites 4a (0,0,0), 4d (0.75, 0.75, 0.75) and 4c (0.25, 0.25, 0.25). Our analysis of elastic constants and mechanical stability confirms that the alloys FeMnZ (Z = Si, Ge and Sn) are all mechanically stable. The electronic band structure demonstrates FeMnSi with the equilibrium lattice constant has spin polarization of 92.28%. Upon substitution of Si with Ge and Sn, FeMnGe and FeMnSn become true half-metals with energy gaps of 0.536 eV and 0.829 eV, respectively. The p-d orbital hybridization between transition elements and main group elements plays the important role in the formation of half-metallic energy gap. Additionally, when the lattice constant of FeMnSi is tuned from equilibrium 5.33 to 5.40 & Aring;, the total magnetic moment is changes from 0.97 to 1.0 mu B/f.u., and it becomes a true half-metal. The phonon spectra of the three alloys do not exhibit imaginary frequencies, indicating their dynamic stability.

通过对熔炼的Fe2Cr1-xMnxGa样品在不同温度下进行热处理来研究其对合金结构、磁性的影响.结果发现Fe2Cr1-xMnxGa的结构和磁性对热处理非常敏感,且存在一定程度的无序,制备的样品结构随不同条件的热处理发生变化,而结构的变化会进而影响合金的磁性行为.磁化强度会随着退火温度的增加而增加,说明通过热处理,样品的有序度得到提高.而随着Mn含量的掺杂,样品的磁化强度在降低,是由于掺杂的Mn原子使得Fe-Mn自旋磁矩反平行排列造成的.

通过第一性原理计算研究了Co2MnSi1-xZx(Z=B,P,As)Heusler合金的能带结构和自旋极化,同时也证明了具有不同价电子的其他元素Z对Si的取代可以控制费米能级在带隙中的移动.与此同时,随着同种Z元素浓度的变化,晶格参数具有接近线性变化的特征,并且这些合金的能带结构具有相似的特点.不同合金的磁矩随价电子数呈线性变化趋势,符合Slater-Pauling行为.由计算结果可知,当x=0.125左右,Co2 MnSi1-x Px和Co2 MnSi1-x Asx合金具有较好的电子性质和较高的自旋极化.

通过第一性原理计算,比较了 Fe2MnSn合金六角结构和立方结构的能量-体积曲线,预测了 Fe2MnSn合金将以立方反Heusler结构存在,两相之间的能量差约为0.01 eV.实验结果表明,熔炼样品却形成了稳定的六角结构.通过对比立方和六角结构合金的电子结构,发现立方结构的费米能级落在态密度的尖峰处,是一种不稳定的结构,而六角结构的费米能级落在能谷处,可稳定存在.同时,由于两相之间的能量差较小,磁性交换能也会促进六角结构的形成.磁性测量表明,温度为5 K时,六角结构Fe2MnSn的磁矩为5.67μB(μB为波尔磁子,μB=9.274×10-24 A·m2),低于理论预测值,这说明样品中存在一定的无序占位,Mn-Mn之间形成了部分反铁磁,导致分子磁矩低于理论值.

本文通过在Heusler合金Mn2NiSn中掺杂Ni、Co元素对其结构与磁性交换作用变化进行了研究.结果表明,在Mn2-xNi1+xSn体系中,随着Ni逐渐替代Mn,合金结构会由立方XA逐渐向L2,结构转变.由于Ni原子相对于Mn原子具有较小的原子半径,Ni2MnSn相对于Mn2NiSn体积大概收缩1.2％.Mn含量的减少使得最近邻的Mn(A)-Mn(B)间反铁磁交换作用减弱,导致居里温度由x=0时的519 K接近线性的降低到x=1时的340 K.当用Co元素替换部分Mn元素时,即Mn2-yCoyNiSn中,复杂的原子占位使得Mn(A)-Mn(B)交换作用降低的同时伴随着Co-Mn之间铁磁交换作用的增强,两者交换作用的竞争导致居里温度先降低后升高,临界点出现在y=0.3处.在Mn2Ni1-zCozSn体系中,当Co替代部分Ni时,由于Ni-Mn之间的交换作用小于Co-Mn之间的交换作用,交换作用的增强导致居里温度随着Co含量的增加逐渐升高.室温下的饱和磁化强度也随着掺杂量的增大逐渐增大.

本文采用电弧熔炼方法制备了两组Mn50-xCrxNi40In10(x=0,1,2)多晶系列样品,通过改变热处理的冷却速率与Cr掺杂量对样品的相变、磁性以及磁熵变进行了研究.结果 表明,与淬火样品相比,慢冷合金的马氏体相变温度较高.随着Cr含量的增加,奥氏体的磁化强度逐渐降低,而马氏体的磁化强度逐渐增强.与淬火样品相比,慢冷样品在相变温度附近,奥氏体和马氏体的磁化强度增强.这主要是由于慢冷样品的原子有序度较高,从而导致其较高马氏体相变温度以及强磁性.不同的热处理冷却速率对Mn49Cr1Ni40In10合金的磁熵基本没有影响.此外,施加3T磁场时,在Mn49Cr1Ni40In10合金中观察到约为13 J/(kg· K)的大的熵变.

In this paper, phase transformations, magnetic properties and exchange bias of Mn50-xCrxNi42Sn8 (x = 0, 0.4, 0.6, 0.8) polycrystalline samples are investigated. It is found that each of all the alloys has a tetragonal martensite structure at room temperature. The transformation temperature decreases with the increase of Cr content. The maximum magnetization difference between martensite and austenite phase is Delta M = 7.61 emu/g. The change of magnetic properties is mainly related to the change of Mn-Mn distance and the hybridization strength between Ni(A)-Mn(D). The ferromagnetism of martensite can be enhanced by Cr doping. The exchange bias field is observed to reach up to as high as 2624 Oe in Mn50Ni42Sn8 alloy after cooling from room temperature to 5 K in 500 Oe magnetic field, which decreases gradually with the increase of Cr content. Furthermore, the exchange bias field increases first and then followed by a decrease with the increase of the cooling field in Mn49.2Cr0.8Ni42Sn8. This is mainly attributed to the change of the interface exchange coupling between the spin glass state and antiferromagnetic region.

Annealing temperatures and applied magnetic fields are two important parameters for the performance modification of magnetic alloys. This article investigated the effect of different annealing temperatures on crystallization condition, magnetic properties and thermal stability of the amorphous magnetic alloy Co36Fe36Si4.8B19.2Nb4 (at%). Results indicate that the annealing temperature can significantly affect the size and content of precipitated nanocrystals in the amorphous alloy, and the precipitation of nanocrystalline phases can result in the distinct change of magnetic properties and Curie temperature. When the annealing was performed at 595 °C for 30 min under an applied transverse external magnetic field of 9550.0 A·m−1, the amorphous alloy shows excellent soft magnetic properties with the saturation magnetization of alloy reaching 110.00 mA·m2·g−1, the residual magnetic induction intensity of 4 × 10−6 T and the coercivity as low as 57.3 A·m−1. Furthermore, the Curie temperature of the field-annealed samples can reach up to 440 °C, approximately 58 °C higher than that of the as-quenched species.

Two kinds of nanohybrids were synthesized successfully by a microfluidic process through tuning just the temperature.

Magnetic properties of Mn50Ni40In10−xSbx alloys and thermal history effect on the magnetization behavior and magnetic entropy change of Mn50Ni40In9Sb1 have been systematically studied. It indicates that the martensitic transformation temperature gradually increases with the increase of Sb content. Meanwhile, the overall magnetization of austenite decreases and that of martensite increases. The magnetization behavior, the critical magnetic field for martensite-to-austenite transformation and the magnetic entropy are very sensitive to the thermal history effect. The maximum magnetic entropy change is up to 27.1Jkg−1K−1 in Mn50Ni40In9Sb1 alloy under a magnetic field of 30kOe with continuous heating method.

The structure and phase transition of Ni55-x CuxFe18 Ga27 alloys prepared by arc-melting and melt-spinning techniques were systematically investigated in this paper.For arc-melting Ni55-xCuxFe18 Ga27 (x=0,2.5,3.2, 3.5,4,7,10,11,14,16)alloys,the martensitic transformation temperature reduced gradually from 292 K to 125 K with increasing Cu content.Substitution of Ni by Cu enhanced the exchange interaction among neighboring atoms in the transition metals,leading to increasing Curie temperature,except for some individual cases.This characteristic demonstrates that Ni55-x CuxFe18 Ga27 alloys retain their ferromagnetism at even high temperature.The structure of melt-spinning Ni55-xCuxFe18 Ga27 (x=1,2,3,4)alloys maintains pure L21-type with increasing lattice constant,which overcomes theγphase in arc-melting samples.The increase of lattice constant in ribbon reduces exchange interaction between 3d electrons in the transition metals,thus decreases the martensitic transformation temperature.

We investigate the band structure, magnetism and density of states of half-Heusler compounds [Formula: see text] [Formula: see text] based on the first-principle calculations. Combined with molecular orbital hybridization theory, we discuss the influence of the main-group element on half-metallic properties of [Formula: see text]. It is found that the replacement of Ge for Si in CoCrSi can adjust the position of the Fermi level, and while it has no impact on the energy gap width and magnetic structure. However, the substitution of P for Si can effectively adjust the magnetism without disrupting its half-metallicity. Our results demonstrate that the electronic structure of [Formula: see text] is mainly dependent on the number of valence electrons of the main-group element.

The structure magnetism and ordering transition of the ferromagnetic shape memory alloy Mn2-xNiGa1+x have been systematically studied in this paper. With increasing Ga content, the structure of the parent phase Mn2-xNiGa1+x is transformed from Hg2CuTi-type to Cu2MnAl-type Heusler alloy gradually. Its lattice constant increases first and then decreases, reaching its maximum at x = 0.3. The sample displays both the primary phase of Heusler and the Ni2In-type hexagonal phase in precipitate form when x lies in the range of 0.3-0.8. The Curie temperature of the primary phase of Heusler alloy Mn2-xNiGa1+x reduces gradually from 590 K for Mn2NiGa to about 220 K for Ga2MnNi with the decrease of the exchange interaction between 3d electrons in the transition metals. However, the variation of Curie temperature of Ni2In-type hexagonal phase is gentle. The separation of Curie temperatures between the Ni2In-type hexagonal phase and the primary phase of Heusler occurs when x lies in the range from 0.6 to 0.8. Substitution of Mn by Ga has a significant influence on the coupling interaction among various atoms, leading to first increasing and then decreasing of the saturated magnetization of Mn2-xNiGa1+x at low temperatures. That is, the saturated magnetization will rise for x <= 0.4 and drops sharply for x > 0.4. Results of differential scanning calorimeter show that the melting temperature decreases gradually as x increases. Meanwhile, the transition temperature from parent phase (B2) to Heusler phase decreases first and increases later.

Based on the metal magnetic memory testing(MMMT),the relationship between the magnetic memory signals and the stress concentration degree for Q235steels static tensile test under different conditions are investigated.Then the magnetic domains at different points with various stresses on the sample are observed.The results show that from elastic stage to enhancement stage the amplitude of magnetic memory signals increases as the stress concentration and diameter of hole increases,magnetic domain distribution becomes intensive gradually,the width of magnetic domain becomes smaller,and the number increases.This study would provide experimental basis for the investigation of stress-magnetic effect on ferromagnetic material,which can be a reference for further quantitative research.

The structures, the martensitic transformations, and the magnetic properties are studied systematically in Mn50Ni40-xCuxIn10, Mn50-xCuxNi40In10, and Mn50Ni40In10-xCuxalloys. The partial substitution of Ni by Cu reduces the martensitic transformation temperature, but has little influence on the Curie temperature of austenite. Comparatively, the martensitic transformation temperature increases and the Curie temperature of austenite decreases with the partial replacement of Mn or In by Cu. The magnetization difference between the austenite phase and the martensite phase reaches 70 emu/g in Mn50Ni39Cu1In10; a field-induced martensite-to-austenite transition is observed in this alloy.

The magnetic and martensitic transformation properties of partially Sb doped In in Mn50Ni40In10 alloy were studied.It was found that the critical temperature of the reverse martensitic transformation TM increased and the Curie temperature TC decreased with increasing Sb concentration xin Mn50Ni40In10-xSbxalloys.The raising of TM was due to the variations of the electronic concentration and lattice volume as well as hybridation of the electronic orbits.As Sb concentration xis less than 0.6,the saturated magnetization differenceΔM between martensite and austenite increased with Sb doping.However,as Sb concentration xis above 0.6,ΔMdecreased with Sb doping.It is noted thatΔMincreased rapidly to 74emu/g as x=0.6 in a field of 20kOe,and a field-induced martensite to austenite transformation was observed in this alloy,indicating the potential application as the magnetic actuation materials.

We found that the martensitic transformation in Mn50Ni33.5Sn8Co8.5 alloy is very sensitive to the surface stress produced during grinding. The grinding-induced martensite in a Mn50Ni33.5Sn8Co8.5 alloy is found to be more thermally stable than the thermally-induced martensite, as indicated by a large increase in the reverse transformation temperature and its latent heat. Annealing the stress-induced martensite was found effective in restoring the austenite structure. The stress-induced martensite was also found to exhibit much enlarged coercive force of 3kOe, compared to 330Oe for the thermally-induced undeformed martensite. This was attributed to the pinning of domain walls by internal stress. These observations were noted in contrast to that observed in most NiMn-based ferromagnetic martensitic alloys.

In this paper, we investigate the magnetic and martensitic transformation properties of Cu doping partial Ni in Ni50Mn36In14 alloy. It is found that the critical temperature of the martensitic transformation decreases with Cu concentration x in Ni50-xCuxMn36In14 increases. While Cu concentration is less than 5% at., the magnetization of austenite phase is stronger than that of martensite phase, and ΔM of magnetization martensite and austenite increases with Cu doping. ΔM increases rapidly to 80 emu/g when x=4.5 and a field-induced transformation is observed in this alloy, predicting the application potential as the magnetic actuation and magnetoresistance materials. As Cu content increases to x > 5, the magnetization of austenite becomes weaker than that of martnensite, ΔM decreases to near zero.