Magnetic properties of misch-metal partially substituted Nd–Fe–B magnets sintered by dual alloy method

The misch-metal(MM) partially substituted Nd–Fe–B sintered magnets were fabricated by the dual alloy method,and the crystal structure, microstructure, and magnetic properties were analyzed comprehensively. X-ray diffraction(XRD)reveals that the increasing content of the MM has an inconsiderable effect on the crystallographic alignment of the magnets.Grains of the two main phases are uniformly distributed, and slightly deteriorate on the grain boundary. Due to the diffusion between the adjacent grains, the MM substituted Nd–Fe–B magnets contain three types of components with different Ce/La concentrations. Moreover, the first-order reversal curve(FORC) diagram is introduced to analyze the magnetization reversal process, coercivity mechanism, and distribution of reversal field in magnetic samples. The analysis indicates that there are two major reversal components, corresponding to the two different main phases. The domain nucleation and growth are determined to be the leading mechanism in controlling the magnetization reversal processes of the magnets sintered by the dual alloy method.     

Large inverse and normal magnetocaloric effects in HoBi compound with nonhysteretic first-order phase transition

HoBi single crystal and polycrystalline compounds with NaCl-type structure are successfully obtained, and their magnetic and magnetocaloric properties are studied in detail. With temperature increasing, HoBi compound undergoes two magnetic transitions at 3.7 K and 6 K, respectively. The transition temperature at 6 K is recognized as an antiferromagnetic-to-paramagnetic (AFM-PM) transition, which belongs to the first-order magnetic phase transition (FOMT). It is interesting that the HoBi compound with FOMT exhibits good thermal and magnetic reversibility. Furthermore, a large inverse and normal magnetocaloric effect (MCE) is found in HoBi single crystal in the $H|| [100]$ direction, and the positive $\Delta S_{\rm M}$ peak reaches 13.1 J/kg$\cdot$K under a low field change of 2 T and the negative $\Delta S_{\rm M}$ peak arrives at $-18 $ J/kg$\cdot$K under a field change of 5 T. These excellent properties are expected to be applied to some magnetic refrigerators with special designs and functions.     

OSCILLATORY INTERLAYER COUPLING WITH Cu AND Zr UNDERLAYER THICKNESS FOR Co/Cu MULTILAYERS

Oscillatory behavior (with a period of about 9 nm) of antiferromagnetic coupling with the thicknesses of Cu and Zr underlayers is reported for sputtered Co(1 nm)/Cu(2.3 nm) multilayers. The related oscillation of magnetoresistance is also observed. Based on the analysis of X-ray diffraction patterns, the variation of crystallographic orientation and modulation period is proved not responsible to the phenomenon. But the underlayer strongly affects the growth orientation of multilayer.     

二维衍射光栅在彩虹全息中的应用

提出了将正交位相光栅和扇出光栅应用于制作彩虹全息图的方法,分析了正交位相光栅产生的多重全息像的位置和强度分布,给出制作扇出光栅的一种实用方法,并给出了实验结果。     

STRUCTURE AND SUPERCONDUCTIVITY OF Mg(B1-xCx)2 COMPOUNDS

In this paper, we report on the structural properties and superconductivity of Mg(B_1-xC_x)₂ compounds. Powder X-ray diffraction results indicate that the samples crystallize in a hexagonal AlB₂-type structure. Due to the chemical activity of Mg powders, a small amount of MgO impurity phase is detected by X-ray diffraction. The lattice parameters decrease slightly with the increasing carbon content. Magnetization measurements indicate that the non-stoichiometry of MgB₂ has no influence on the superconducting transition temperature and the transition temperature width. The addition of carbon results in a decrease of T_c and an increase of the superconducting transition width, implying the loss of superconductivity.     

STRUCTURE AND SUPERCONDUCTIVITY OF Mg1-xLixB2

The effects of the substitution of Li for Mg in Mg_1-xLi_xB₂(x=0,0.1,0.2) on their structure and superconductivity have been investigated. It has been found by X-ray diffraction that the substitution of Li for Mg with x=0.1 and 0.2 does not cause phase transformation in these samples. However,the measurements of temperature-dependent normalized magnetization indicate the loss of superconductivity with the increase of Li content in these samples.     

(Au,Ag)/Si复合纳米颗粒薄膜的微结构与光谱特性

采用复合靶共溅射方法制备了(Au,Ag)/Si复合纳米颗粒薄膜,分别采用Maxwell-Garnett理论和微分有效媒质(DEM)理论计算了Ag/Si复合薄膜的吸收光谱,实验测量结果与DEM理论计算更接近,讨论了(Au,Ag)/Si体系复合薄膜共振吸收峰宽化的微观机制. 关键词：     

Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method

MM_(14)Fe_(79.9)B_(6.1)/Nd_(13.5)Fe_(80.5)B_6 magnets were fabricated by dual alloy method(MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T_(c1)corresponds to the main phase which contains more La Ce, and T_(c1) decreases from 276.5?C to 256.6?C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of Br with the increase of MM indicates the existence of inter-grain exchange coupling in the magnets. When MM/R ≤ 30.3 at.%,the magnetic properties can reach the level of the intrinsic coercivity Hcj≥ 7.11 kOe and the maximum energy product(BH)max≥ 41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process,and this will cause the decrease of H_(cj) Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.     

Composition design for (PrNd-La-Ce)_2Fe_(14)B melt-spun magnets by machine learning technique

Data-driven technique is a powerful and efficient tool for guiding materials design,which could supply as an alternative to trial-and-error experiments.In order to accelerate composition design for low-cost rare-earth permanent magnets,an approach using composition to estimate coercivity(H_(cj)) and maximum magnetic energy product(BH)_(max) via machine learning has been applied to(PrNd–La–Ce)_2Fe_(14)B melt-spun magnets.A set of machine learning algorithms are employed to build property prediction models,in which the algorithm of Gradient Boosted Regression Trees is the best for predicting both H_(cj) and(BH)_(max),with high accuracies of R~2= 0.88 and 0.89,respectively.Using the best models,predicted datasets of H_(cj) or(BH)max in high-dimensional composition space can be constructed.Exploring these virtual datasets could provide efficient guidance for materials design,and facilitate the composition optimization of 2:14:1 structure melt-spun magnets.Combined with magnets' cost performance,the candidate cost-effective magnets with targeted properties can also be accurately and rapidly identified.Such data analytics,which involves property prediction and composition design,is of great time-saving and economical significance for the development and application of La Ce-containing melt-spun magnets.     

Machine learning technique for prediction of magnetocaloric effect in La(Fe,Si/Al)_(13)-based materials

Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La(Fe,Si/Al)_(13)-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree(GBRT) to essentially find the correlation between the Curie temperature(T_C), maximum value of magnetic entropy change((?S_M)_(max)),and chemical composition, all of which yield high accuracy in the prediction of T_C and(?SM)_(max). The performance metric coefficient scores of determination(R~2) for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.