This study systematically investigates the hydrogenation behavior of N35-type sintered NdFeB magnets and its consequential effects on their mechanical and magnetic properties. The hydrogenation follows a distinct two-stage mechanism: hydrogen first preferentially reacts with the Nd-rich grain boundary phase to form brittle neodymium hydrides (NdHx), before penetrating the main Nd2Fe14B phase to form Nd2Fe14BHx. This process, driven by alloy hydrogen trapping, induces severe microstructural damage through cracking and interfacial debonding. The hydrogen-induced degradation leads to a catastrophic decline in mechanical properties across scales. Macroscopically, the elastic modulus decreases by 10.6 GPa and compressive strength drops by 269 MPa. At the micro-scale, a dramatic collapse in nanohardness is observed: the average value plummets from initial levels of 13.37 GPa (main phase) and 2.84 GPa (Nd-rich phase) to merely 0.94 GPa after hydrogenation. In parallel, magnetic properties are severely impaired, with coercivity and maximum magnetic energy product decreasing by 1.60 kOe and 5.3 MGOe, respectively, due to the destruction of domain wall pinning sites and nucleation of reverse domains at hydrogen-generated microcracks. These findings provide a quantitative characterization and correlative analysis linking hydrogen-driven microstructural evolution to macroscopic performance decay. The insights are crucial for designing hydrogen-resistant magnets, predicting service life in hydrogen-containing environments, and optimizing recycling processes via hydrogen decrepitation.

To enhance the high-temperature coercivity and thermal stability of sintered Nd-Fe-B magnets, this study employs low-melting-point Dy-Al eutectic alloys (Dy₉₅Al₅, Dy₉₀Al₁₀, Dy₈₅Al₁₅) as diffusion sources via magnetron sputtering and heat treatment. Systematic investigation reveals that the synergistic effect of Dy and Al is crucial for performance improvement, operating through dual mechanisms: “main-phase hardening” and “grain boundary optimisation.” Dy penetrates along optimised grain boundaries to form (Nd, Dy)₂Fe₁₄B core-shell structures on main-phase grains, hindering reverse domain nucleation. Simultaneously, Al improves the wettability and continuity of the grain boundary phase, enhancing intergranular decoupling and providing efficient channels for Dy diffusion. Among the investigated compositions, Dy₉₀Al₁₀ shows the best overall performance, which yields the highest coercivity increase from 13.39 kOe to 22.40 kOe (a 67.3

This study developed a high-strength, high-ductility Mg–Li alloy by combining Sm/Sn alloying with high-pressure heat treatment. The as-cast alloy with 2 wt% Sm exhibits the optimal comprehensive properties. Subsequent high-pressure heat treatment (6 GPa, 1100 °C, 0.5 h) of the Mg-6Li-2Sn-2Sm alloy induces a remarkable microstructural reconstruction, resulting in a multiscale heterostructure comprising discretely distributed Mg3Sm/Mg2Sn composite particles along the as-cast network, a uniform dual-phase matrix constituted by microscale cellular α-Mg and the β-Li phase, and nanoscale needle-like α-Mg precipitates dispersed within the β-Li phase. This architecture synergistically activates multiple strengthening mechanisms, including grain refinement, precipitation strengthening, and hetero-deformation induced strengthening, endowing the alloy with a compressive yield strength of 273 MPa, an ultimate compressive strength of 439 MPa, and a maximum engineering strain of 59.3%, thereby achieving an exceptional strength-ductility synergy. This work provides novel insights into microstructural design and processing strategies for developing low-cost, high-performance Mg–Li alloys.

Bulk and ribbon Er2Tm2Al4CuNiGa high-entropy-alloy (HEA) were successfully synthesized by arc-melting method and amorphous engineering, respectively. X-ray diffraction experiment (XRD), differential scanning calorimetry (DSC) traces and high resolution transmission electron microscope (HRTEM) indicate that bulk sample crystalizes in form of polycrystalline while ribbon sample is amorphous. By amorphous engineering, the magnetic transition temperature was reduced below liquid helium temperature and low-field magnetocaloric effect (MCE) was greatly enhanced. The magnetic ordering temperatures were determined as 4.5 K and similar to 3.0 K for bulk and ribbon samples, respectively. The maximum value of magnetic entropy change increases from 2.7/6.7 J/kgK for bulk sample to 4.3/9.0 J/kgK for typical ribbon sample R52 under field changes of 0-1/0-2 T. Furthermore, ribbon samples show the characteristic of second order magnetic transition based on Arrott plots, indicating of good magnetic and thermal reversibility. The large low-field MCE of ribbon Er2Tm2Al4CuNiGa HEA at liquid helium temperature indicates that amorphous engineering is an effective method to improve the performance of magnetic cooling materials.

Low-temperature magnetocaloric materials are of great importance for potential applications of gas liquefaction such as nitrogen, hydrogen and helium for their low liquidation temperatures (similar to 4 K for helium, similar to 20 K for hydrogen and similar to 77 K for nitrogen respectively), of which the working temperature, the maximal magnetic entropy change ((-Delta S-M)(max)), the maximal adiabatic temperature change ((Delta T-ad)(max)), and the temperature average entropy change (TEC) are the key assessment parameters. Herein, we designed and synthesized Er1-xTmxGa series compounds based on the optimization of the spin quantum number (Spin) with their magnetic ordering temperature successfully adjusted from 31.0 K to 15.0 K, which covers the liquid hydrogen temperature range. Particularly, Er0.8Tm0.2Ga shows outstanding (-Delta S-M)(max), TEC(20), and (Delta T-ad)(max) values of 13.6 J/kg K, 10.1 J/kg K, and 4.3 K under the field change of 0-2 T, respectively, which are increased by 32.0 %, 36.4 %, and 48.2 % compared with the parent ErGa compound. It should be noted that the refrigerant capacity (RC) of Er0.8Tm0.2Ga is not only larger than ErGa but also larger than TmGa. Furthermore, neutron powder diffraction (NPD) was employed on Er0.8Tm0.2Ga to reveal the physical mechanism of its enhanced magnetocaloric effect (MCE). It is found that for Er0.8Tm0.2Ga the more pronounced order-to-disorder transition than the spin reorientation (SR) transition, the characteristic second order phase transition, and the existence of the short-range magnetic ordering above the magnetic ordering temperature should be jointly responsible for its large magnetocaloric effect.

Exploring and comprehending magnetocaloric materials with spin reorientation (SR) phase transition is of vital importance for practical applications of magnetocaloric effect (MCE). Herein, this study presents a systematic study on the magnetic properties, heat transport properties, magnetic structure, and electronic structure of NdNi compound. NdNi is observed to undergo an SR phase transition and a ferromagnetic (FM) to paramagnetic (PM) phase transition successively with increasing temperature. Neutron powder diffraction (NPD) experiment reveals that the SR phase transition involves the rotation of Nd magnetic moment from a‐axis to the direction with a deviation angle θ in ac‐plane upon temperature decreasing, whereas Ni does not contribute to the total magnetic moment. These theoretical investigations based on the first‐principles calculations and the second‐order perturbation theory further confirm that the SR phase transition is closely associated with magnetocrystalline anisotropy energy, which is mainly contributed by Nd atoms. The presence of SR phase transition makes NdNi possess a wide refrigerant temperature span, thus merits it as a magnetic cooling material for applications with various temperature ranges. This work provides profound insights for further exploring and comprehending multiple‐phase‐transition magnetocaloric materials.

The equiatomic quaternary Heusler alloy FeRuCrSi was synthesized and its atomic ordering, magnetic properties and electronic structure were investigated experimentally and theoretically. The FeRuCrSi formed a single Heusler phase and had a lattice constant of 5.811 & ANGS; at room temperature. An L21B-type disorder related to the random occupation of Fe and Ru at 4a and 4b sites was identified in the X-ray diffraction pattern. The Curie temperature of FeRuCrSi was 346 K and the saturation magnetization at 5 K was 1.84 & mu;B/f.u., which is smaller than the integral value of 2.00 & mu;B required for ideal spin gapless semiconductor character and is likely related to the L21B-type disorder. First-principles calculations revealed that ordered FeRuCrSi with YII-type structure had the lowest total energy at 0 K. However, the energy difference between it and the L21B structure was only 0.09 eV/f.u., thus the L21B disorder dominated in the experimental sample because of the enthalpy of mixing and the "freezing" of high-temperature disorder at room temperature. The YII-type FeRuCrSi was a SGS with a half -metallic gap in the minority density of states (DOS) and a zero-width gap in the majority DOS. However, the L21B-type disorder disturbed the SGS character by narrowing the two gaps. The total spin moment of ordered FeRuCrSi was 2.00 & mu;B/f.u., mainly determined by the antiparallel coupled Cr and Fe/Ru spin moments. However, the total moment was slightly reduced in L21B-type FeRuCrSi. All this suggests that the possible L21B disorder should be carefully considered when designing and synthesizing half-metals/SGS in Heusler alloys for spintronic applications.

The atomic ordering, electronic structure, magnetic properties and martensitic transformation of three new all-dmetal Heusler alloys Mn2PtZ (Z = Sc, Ti and V) have been investigated theoretically to discover new magnetic shape memory alloys (MSMAs). Depending on the different third transition metal element Z, Mn2PtSc and Mn2PtTi tend to form XA structure while Mn2PtV forms L21 structure. This difference is related to their DOS structures. Charge density difference calculations indicate enhanced d-d hybridization in these all-d-metal Heusler alloys. Mn2PtZ are all ferrimagnets with their Mn-Mn or Mn-V local spin moments antiparallel coupled. In these alloys, Mn2PtTi is a possible new MSMA with the energy difference & UDelta;EM between the martensite and austenite as large as -262 meV/f.u., which indicates a high martensitic transformation temperature and is related to the Jahn-Teller effect in the electronic structure. A large volume effect of 2.9% cell shrinkage occurs during the martensitic transformation. All this makes Mn2PtTi a promising candidate for MSMAs with wide applications.

Two new all-d-metal Heusler alloys Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5 are proposed as candidates for magnetic shape memory alloys. In these alloys, the Sc atom prefers occupying the D (0.75, 0.75, 0.75) sites in the Heusler alloy lattice and forms d–d hybridization with its nearest neighbor atoms such as Ni. Martensitic transformation is possible in both Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5. Differing from the "volume-conserving" character in classic Heusler alloys, a large volume shrinkage of 2.3% and 2.8% occurs in Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5 during the martensitic transformation, respectively. The magnetization difference between the austenite and martensite is as large as 4.50 μB/f.u. for Mn2Ni1.5Sc0.5 and 4.49 μB/f.u. for Ni2Mn1.5Sc0.5, due to the ferromagnetic–antiferromagnetic magnetic transition coupling with the martensitic transformation. The parallel coupled Mn (B) and Mn (D) spin moments in the austenite become antiparallel in the martensite, which leads to the large decrease of magnetization after the martensitic transformation. The energy difference ΔEM between the martensite and austenite is −45.5 and −25.9 meV/f.u. for Mn2Ni1.5Sc0.5 and Ni2Mn1.5Sc0.5, respectively. The large ΔEM of Mn2Ni1.5Sc0.5 derives from the strong Jahn–Teller effect in its density of states structure and makes it a promising candidate for magnetic shape memory alloys.

La0.8Ce0.2Fe11.7-xMnxSi1.3 master alloys were prepared by medium frequency induction furnace,then annealed,saturatedly hydrogenated,and finally crushed into powders.The multiple components of La0.8Ce0.2Fe11.7-xMnxSi1.3H1.8(x=0.23,0.26,0.29,0.32,wt％)powders with the Curie temperature(TC)interval of 5 K were mix-bonded by epoxy resin to extend the full width at half maximum of magnetic entropy of alloy.The magnetic properties of the mix-bonded specimens were measured by VersaLab and adiabatic temperature change direct test device.The maximal magnetic entropy change of the mix-bonded specimens is decreased,whereas the full width at half maximum of magnetic entropy and the relative cooling power are increased,compared with those of the single-component-bonded specimens.The maximal relative cooling power is 139.2 J/kg for the four-component-bonded specimen.

制备(Fe81.5Co1.5Ga17)100-xTbx(x=0,0.05,0.10,0.15,0.20)系列合金铸锭,探究了Tb元素添加对Fe81.5Co1.5Ga17合金结构及其磁性能的影响.结果表明,该系列合金均以无序α-Fe体心立方结构为主,加入Tb元素后合金晶格常数增加,I200/I110相对峰强度变化与晶格常数变化趋势一致,合金在[100]晶向择优取向.Tb元素的添加使合金析出富Tb相,并使合金晶粒细化.随着Tb元素含量的增加,合金中分布的富Tb相由分散状态逐渐变为连续的网状结构,并产生枝状晶.(Fe81.5Co1.5Ga17)100-xTbx合金的饱和磁致伸缩系数随x值的增大呈先增大后减小的趋势,x=0.10时合金的饱和磁致伸缩系数达到217×10-6,相比x=0的合金提升11％.该系列合金中,当磁场小于40 kA/m时,x=0的合金的磁致伸缩率最大;当磁场为40～80 kA/m时,x=0.10的合金的磁致伸缩率最大;当磁场为80～120 kA/m时,x=0.20的合金的磁致伸缩率最大;磁场大于120 kA/m后,合金的磁致伸缩基本达到饱和,x=0.10,0.15的合金具有高饱和磁致伸缩系数.该系列合金饱和磁化强度值随Tb元素的增加先增后降,x=0.05时合金的饱和磁化强度达到最大,为210.06 emu/g.

A series of Ni50Mn36.5Sb13.5-xSix (x = 0 - 2.5) Heusler alloys was prepared. Effect of Si-doping on the formation, martensitic transformation and magnetic properties of Ni-Mn-Sb alloys was investigated experimentally and theoretically. The increasing Si content leads to the increase of the Curie temperature TC and decrease of the saturation magnetization Ms at 5K. The martensitic transformation temperature Tm also shows a decreasing tendency with the substitution of Si for Sb. First-principles calculations indicate that the martensite has a lower total energy comparing with the austenite, which supports the phase transition observed experimentally. The energy difference between the martensite and austenite Delta EM suggests that the martensitic transformation temperature TM will decrease with a small amount of Si-doping, but increase when Si content is high. This explains the decrease of TM observed in the experimental samples, for in these samples, the Si content is in the Delta EMdecreasing region. The calculated total spin moment of the martensite shows a decreasing tendency with increasing Si content, which agrees with the variation of saturation magnetization Ms at 5K.

以氯化钕溶液为原料液,碳酸氢铵为沉淀剂,采用正加沉淀法和并流沉淀法的加料方式制备了碳酸钕,经高温焙烧后得到氧化钕.运用XRD、SEM、粒度分析等表征手段,考察了加料方式、沉淀剂浓度、晶种、沉淀温度和沉淀时间对氧化钕的粒度、形貌、晶型、稀土总量(REO)和Cl-含量等理化性能的影响.结果表明,45℃～60℃的沉淀温度,所制备碳酸钕沉淀的晶相结构均为Nd2(CO3)3·2.5H2O.升高沉淀温度或者延长沉淀时间均可以将氧化钕粉体的形貌由分散的针状结构逐渐演变成具有花束状结构的团聚体.根据不同的沉淀条件,可以制备出不同粒度范围的氧化钕粉体,即采用并流沉淀法的加料方式,通过升高沉淀温度、延长沉淀时间和添加晶种,易制得大粒度氧化钕产品(D50＞15 μm);采用正加沉淀法的加料方式,通过低温、缩短沉淀时间,易制得小粒度氧化钕产品(D50＜15 μm).

制备目标成分为Fe83-xCoxGa17(x=0,0.5,1.5,2.5,3.5)系列的合金铸锭,研究了Co元素添加对该系列合金结构、磁致伸缩性能、磁性能及硬度的影响.实验结果表明,随着Fe-Ga合金中Co元素的增加,合金饱和磁致伸缩值先增加后降低,在x=1.5时,合金饱和磁致伸缩值最高,达到195·10-6,并且该成分合金在低场下具有高的磁致伸缩率.同时还发现,Fe83-x Cox Ga17系列合金相结构均为无序α-Fe体心立方结构,并且Co元素添加后,合金产生晶格畸变,该系列合金晶格常数随Co元素加入的变化表现为先减小后增大,与饱和磁致伸缩值先增后减的变化相对应.加入适量的Co元素还可以提高Fe-Ga升合金的饱和磁化强度,在x=1.5时达到195.6 emu/g,同时降低合金矫顽力,并提高合金硬度,在x=3.5时,合金硬度相比于Fe-Ga合金提升近15％.

To satisfy the application of different environments, grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance. In this paper, the alloys were prepared by mixing different ratios of the master alloy (Ce,Pr,Nd)-Fe-B and the sintering aid (Pr,Nd)-Al. The coercivity of sintered (Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt% of (Pr,Nd)-Al, while the maximum energy product decreases slightly. We systematically investigated the corrosion behavior and microstructure of the sintered magnets in order to determine the mechanism of the degradation. The sintered (Ce,Pr,Nd)-Fe-B magnets with 2 wt% of (Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others, due to the distribution of intergranular phases. The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al, improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd, Pr or Ce. In addition, the element distribution of the magnets doped by (Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability. Therefore, intergranular adding ternary (Pr,Nd)-Al alloy powders results in both high coercivity and good corrosion resistance synchronously.

采用X射线衍射法、振动样品磁强计法和电阻应变计法研究了退火前后Pr x Tb 1-x Fe 1.9 Ti 0.1 合金的晶体结构、磁性和磁致伸缩性能。X射线衍射分析发现,当Pr含量低于0.4时,退火前后合金的主相不变均为Laves相,当Pr含量高于0.4时,退火后合金的主相由Laves相转变为了1∶3相。磁性测量表明Pr x Tb 1-x Fe 1.9 Ti 0.1 合金的饱和磁化强度随着Pr含量的增加而降低。磁致伸缩的测量结果表明,当Pr含量低于0.4时,退火处理可提高合金的磁致伸缩性能,退火处理的Pr 0.2 Tb 0.8 Fe 1.9 Ti 0.1 合金的磁致伸缩系数达到1733×10 -6 。

为改善多晶Fe-Ga合金的磁致伸缩性能,在Fe-Ga合金中掺杂稀土Ce、Tb和Dy元素。研究了Fe 83 Ga 17 和Fe 83 Ga 17 R 0.6 （R=Ce,Tb,Dy）合金的相结构和磁致伸缩性能。结果表明,Fe 83 Ga 17 合金由单一bcc结构Fe（Ga）固溶体相组成,而掺杂稀土后的Fe 83 Ga 17 R 0.6 合金中除保持bcc结构的Fe（Ga）固溶体相外,还出现了R 2 Fe 17 第二相。掺杂稀土后的Fe 83 Ga 17 R 0.6 合金磁致伸缩系数明显大于Fe 83 Ga 17 合金。掺杂不同种类的稀土元素对Fe-Ga合金磁致伸缩性能改善的程度不同。在外磁场为557 k A/m时,Fe 83 Ga 17 R 0.6 合金的磁致伸缩系数(206×10 -6 )明显大于Fe 83 Ga 17 Tb 0.6 (165×10 -6 )和FFe 83 Ga 17 Dy 0.6 (161×10 -6 )合金的磁致伸缩系数。

In order to improve magnetostrictive properties of the polycrystalline Fe-Ga alloys, rare earth elements Ce, Tb and Dy were doped into Fe-Ga alloys. The microstructures and magnetostrictions of Fe83Ga17 and Fe83Ga17R0.6 (R=Ce, Tb, Dy) alloys were studied. The results indicate that Fe83Ga17 alloy consists of a single Fe(Ga) solid solution phase with bcc structure. However, the Fe83Ga17R0.6(R=Ce, Tb, Dy) alloys are composed of the Fe(Ga) solid solution phase and a small amount of R2Fe17 secondary phase. The magnetostriction coefficients of the Fe83Ga17R0.6(R=Ce, Tb, Dy) alloys are significantly larger than that of the Fe83Ga17 alloy. The improvement degree of magnetostrictive properties of Fe-Ga alloy varies with different rare earth elements doped into the alloy. The magnetostriction coefficient of Fe83Ga17Ce0.6 alloy (206x10(-6)) is larger than that of the Fe83Ga17Tb0.6 (165x10(-6)) and Fe83Ga17Dy0.6 (161x10(-6)) at the magnetic field of 557 kA/m.

为改善多晶Fe-Ga合金的磁致伸缩性能,在Fe-Ga合金中掺杂稀土Ce、Tb和Dy元素.研究了Fe83Ga17和Fe83Ga17R0.6(R=Ce,Tb,Dy)合金的相结构和磁致伸缩性能.结果表明,Fe83Ga17合金由单一bcc结构Fe(Ga)固溶体相组成,而掺杂稀土后的Fe83Ga17R0.6合金中除保持bcc结构的Fe(Ga)固溶体相外,还出现了R2Fe17第二相.掺杂稀土后的Fe83Ga17R0.6合金磁致伸缩系数明显大于Fe83Ga17合金.掺杂不同种类的稀土元素对Fe-Ga合金磁致伸缩性能改善的程度不同.在外磁场为557 kA/m时,Fe83Ga17Ce0.6合金的磁致伸缩系数(206× 10-6)明显大于Fe83Ga17Tb0.6 (165× 10-6)和Fe83Ga1 7Dy0.6(161×10-6)合金的磁致伸缩系数.

•The CeGa2 phase existing in the Fe83Ga17Ce0.8 alloy is found for the first time.•The (100) orientation of alloy become stronger after Ce doping into the Fe-Ga alloy.•The melt-spinning leads to the formation of asymmetrical DO3 phase.•The enhanced magnetostriction is credited with new phase and preferred orientation.•The Ce-doping and melt-spinning are beneficial to the improvement of magnetostriction.