Effect of Ti layer thickness on microstructure and magnetic properties of Ti/Co/Ti films

TiCoTi granular films were prepared by DC facing-target magnetron sputtering system onto glass substrates and subsequently in situ annealing in vacuum. Structural of Ti ( t nm)/Co (40 nm)/Ti ( t nm) films were investigated in detail, which shows that the majority Co nanograins are formed as the hexagonal-close-packed (HCP) structure. Vibrating sample magnetometer (VSM) and scanning probe microscope (SPM) were applied to study the magnetic properties, morphologies and domain structures of these samples. It has been found that the structure and magnetic properties of the Ti/Co/Ti films depend strongly on the Ti layer thickness. The out-of-plane coercivities ( Hc) of the film is maximum about 78.8 kA·m-1 when t =5 nm with annealing at 300 ℃; the distributing of grains of the sample is uniformity; and the average size of particles is about 13 nm. The obtained results suggest that this system is perpendicular anisotropy and might be applicable to perpendicular magnetic recording media.     

Design and Qualification of Pr–Fe–Cu–B Alloys for the Additive Manufacturing of Permanent Magnets

The direct use of an advanced binder-free additive manufacturing technique, namely laser powder bed fusion (L-PBF), does not easily allow obtaining variously shaped, fully dense Nd–Fe–B magnets with high coercivity. The process inherently leads to the re-melting of the powder and appearance/disappearance of undesired/desired microstructural features responsible for low and large coercivity. In this work, the development of a useful microstructure responsible for high coercivity in Pr₂₁Fe_73.5Cu₂B_3.5 and Nd₂₁Fe_73.5Cu₂B_3.5 alloys and a possible way to produce fully dense permanent magnets via additive manufacturing processes is demonstrated using: (i) suction casting technique, which provides a high cooling rate and thus similar microstructures as in L-PBF but requires only very small amounts of powder; (ii) conventional L-PBF processing using kg of powder, and (iii) a subsequent annealing treatment that is similar to a conventional sintering treatment. The subsequent heat treatment is necessary to develop high coercivity by forming a novel microstructure: hard magnetic (Nd,Pr)₂Fe₁₄B grains embedded in a matrix of intermetallic (Nd,Pr)₆Fe₁₃Cu phase. Furthermore, it is demonstrated that Pr₂₁Fe_73.5Cu₂B_3.5 exhibits a higher coercivity than Nd₂₁Fe_73.5Cu₂B_3.5 because of a finer and more homogeneous grain size distribution of the Pr₂Fe₁₄B phase. The final L-PBF printed Pr₂₁Fe_73.5Cu₂B_3.5 samples provide a coercivity of 0.75 T.     

电力电子中高频软磁材料的研究进展

随着电力电子行业的飞速发展,新型电磁材料的投入使用,对电子元器件的高频磁性能提出了新的要求。磁芯作为电子元器件的核心部件,其发展程度直接决定电子元器件的性能,这就要求具有优异高频软磁性能的材料发展。本文综述了四种软磁材料的发展历程,对每种软磁材料的优缺点进行了归纳总结,同时指出了未来的发展方向,并重点对近年来研究热门的软磁复合材料进行了梳理。粒径大小可控、包覆层对核层的包覆均匀程度以及从实验室走向产业化的大批量制备方法是未来高频软磁复合材料的发展趋势。     

The influence of silicon content on physical properties of non-oriented silicon steel

Electric motors make up a large portion of our global electricity consumption and have enjoyed a long history doing so. Electrical steels are popularly used materials in electric motors to improve their performance. This has made them prime candidates for increasing the energy efficiency of electric motors, especially given concerns regarding energy conservation. Now manufacturers of electrical steels have been prompted to seek increasingly efficient electrical steels to provide a more competitive product. This literature review focuses on one specific metallurgical aspect – the defining trait of electrical steels; silicon content and its resulting influence on the physical properties. From the literature review it is concluded that the application requirement and functionality must be considered thoroughly when deciding silicon content.

This review was submitted as part of the 2017 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged     

Voltage‐Induced Coercivity Reduction in Nanoporous Alloy Films: A Boost toward Energy‐Efficient Magnetic Actuation

Magnetic data storage and magnetically actuated devices are conventionally controlled by magnetic fields generated using electric currents. This involves significant power dissipation by Joule heating effect. To optimize energy efficiency, manipulation of magnetic information with lower magnetic fields (i.e., lower electric currents) is desirable. This can be accomplished by reducing the coercivity of the actuated material. Here, a drastic reduction of coercivity is observed at room temperature in thick (≈600 nm), nanoporous, electrodeposited Cu–Ni films by simply subjecting them to the action of an electric field. The effect is due to voltage‐induced changes in the magnetic anisotropy. The large surface‐area‐to‐volume ratio and the ultranarrow pore walls of the system allow the whole film, and not only the topmost surface, to effectively contribute to the observed magnetoelectric effect. This waives the stringent “ultrathin‐film requirement” from previous studies, where small voltage‐driven coercivity variations were reported. This observation expands the already wide range of applications of nanoporous materials (hitherto in areas like energy storage or catalysis) and it opens new paradigms in the fields of spintronics, computation, and magnetic actuation in general.     

温度对化学镀Co-W-P合金镀层性能的影响

研究了温度对化学镀Co-W-P合金镀层的厚度、成分、表面形貌、耐蚀性和磁性能的影响。结果表明:适当升高温度有利于提高镀速和增加合金镀层的厚度,但当温度高于90℃时,镀液容易发生分解。随着温度的升高,合金镀层中钴的质量分数逐渐增大,而钨和磷的质量分数迅速降低,使得镀层的耐蚀性降低。Co-W-P合金镀层呈现出典型的颗粒结构,表面均匀、致密。高温下合金镀层表面粗糙度增大,使得矫顽力明显下降。     

Fe21Ni79合金纳米线阵列的制备与磁性

用交流电化学沉积方法，在多孔铝阳极氧化膜的柱形孔内制备直径约60 nm，长度约为9.7 μm的Fe₂₁Ni₇₉合金纳米线.采用扫描电镜、透射电镜、X射线衍射仪和振动样品磁强计对纳米线的形貌 、结构和磁学性质进行了测试.结果表明，Fe₂₁Ni₇₉纳米线排列有序，长径比可控，合金呈fcc结构.当将其在外磁场下进行垂直磁化时，磁滞回线出现较高的矩形比0.86，矫顽力达1203Oe.且随着退火温度升高，矫顽力迅速增大，500℃时达到最大值1315Oe，之后又随退火温度的升高而下降.矩形比也呈现类似的变化规律.     

甩带处理TbMn6Sn6化合物的磁性研究

研究了甩带速度对TbMn6Sn6化合物晶体结构和磁性的影响。结果表明,甩带冷却速度对TbMn6Sn6化合物的晶体结构几乎没有影响,主要是由1：6：6型相所构成,其中含有少量铁磁性的Mn3Sn2杂相;随着甩带速度从3900r／min降至1500r／min,试样晶粒尺寸依次为220、170、280和340nm;甩带冷却速度对TbMn6Sn6化合物的室温矫顽力几乎没有影响,以3900r／min甩带制成的TbMn6Sn6化合物的矫顽力,随着温度的升高,从5K下的1600 Oe上升至100K下的11360Oe,然后随着温度继续上升至300K,其矫顽力减小至533Oe。     

Microstructure and magnetic properties of FePt/MgO multilayers deposited by RF magnetron sputtering

FePt (50 nm) and [FePt(a nm)/MgO(b nm)]5/glass (a=1, 2, 3; b=1, 2, 3) films were prepared by radio frequency (RF) magnetron sputtering technique, and then were annealed at 600°C for 30 min. The effect of MgO layer thickness on the structures and magnetic properties of the FePt/MgO multilayers was investigated. The coercivities and inter-grain interactions of the FePt/MgO films were decreased, yet the degree of (001) texturing drastically increased with the increase in MgO layer thickness when the FePt layer thickness was fixed. Thus, the FePt/MgO films with appropriate coercivities, high perpendicular anisotropy, and weak in-ter-grain interactions were obtained by controlling the MgO layer thickness. Overall, these results indicate that the FePt/MgO nanos-tructured films are promising candidates for future high-density perpendicular recording media.     

Effect of Ag addition on the microstructure and magnetic properties of FePt thin films

FePt thin films and [FePt/Ag]n multilayer thin films were prepared by magnetron sputtering technique and subsequent annealing process. By comparing the microstructure and magnetic properties of these two kinds of thin films, effects of Ag addition on the structure and properties of FePt thin films were investigated. Proper Ag addition was found helpful for FePt phase transition at lower annealing temperature. With Ag addition, the magnetic domain pattern of FePt thin film changed from maze-like pattern to more discrete island-like domain pattern in [FePt/Ag]n multilayer thin films. In addition, introducing nonmagnetic Ag hindered FePt grains from growing larger. The in-depth defects in FePt films and [FePt/Ag]n multilayer films verify that Ag addition is attributed to a large number of pinning site defects in [FePt/Ag]n film and therefore has effects on its magnetic properties and microstructure.