Effect of La doping on structural, magnetic and microstructural properties of Ba1 − x La x Fe12O19 ceramics prepared by citrate combustion process

La-substituted M-type barium ferrites, Ba_{1 − x} La _x Fe₁₂O₁₉, with x = 0.00–0.30 were successfully prepared via a citrate combustion process. Properties of the ceramics were characterized by powder X-ray diffraction, vibrating sample magnetometry and scanning electron microscopy. XRD patterns revealed only magnetoplumbite structure without minor phases. With increasing the La substituted content, the saturation magnetization (M _S ) was increased and reached to a maximum at x = 0.15 and then decreased but coercivity (H _C ) was increased. SEM micrographs of the dense ceramics showed the hexagonal platelet shape at low La content and the irregular shape at high La content.     

Influence of HDDR treatment on magnetic properties of TbFe2- and DyFe2-based intermetallics

Magnetic properties of TbFe₂, DyFe₂, Tb(Fe_0.8M_0.2)₂ and Dy(Fe_0.8M_0.2)₂ with M=Co, Al, Si, Ga alloys affected by the Hydrogenation-Decomposition-Desorption-Recombination processing have been studied. After hydrogen treatment the coercive force H_c grows sharply, so HDDR-powders can be used as isotropic permanent magnets with the energy product up to 26 MG Oe at T=77 K. In Dy(Fe_0.8Al_0.2)₂ at T<10 K the stepwise magnetic reversal has been observed. The HDDR-treatment increases the critical field of magnetic reversal from 11 up to 18.4 kOe at 4.2 K. It is shown that the effect of the stepwise magnetic reversal is caused by a heat release in a sample during an avalanche motion of narrow domain walls.     

Magnetic Behavior of Trinuclear Vanadium(II)–Diamine Complexes. Part 2. Large Intramolecular Antiferromagnetic Exchange Interactions in a Triangular Unit

This study reports the magnetic structures of newly reported trinuclear vanadium(II)–diamine complexes. Using the isotropic Heisenberg exchange Hamiltonian, it is suggested that there are strong intramolecular antiferromagnetic interactions among the vanadium(II) ions. It is also suggested that these complexes are good candidates to the geometrically frustrated systems. For part 1 see A. Bayri, J. Inorg. Organomet. Polym. Mater., (in press) An erratum to this article can be found at     

Antiferromagnetic Exchange Interactions. Part 1. Newly Reported Nickel(II) Complex of the Antiprine Schiff Base of 3-Formylsalicylic Acid

This study reports the magnetic properties of newly reported nickel(II) complex of the antiprine Schiff base of 3-formylsalicylic acid. Using the isotropic magnetic interaction model it is suggested that there is a strong antiferromagnetic interactions between metal centers in dimeric units. It is also suggested that the system become demagnetized below a certain temperature. An erratum to this article can be found at     

S=2的单轴各向异性横向Ising模型的基态磁性质

对处于外界横向磁场中,单自旋S=2的具有单轴各向异性场的Ising铁磁体模型,采用平均场理论(MFA),基于Bogoliubov不等式,以Gibbs自由能为判据,推导出系统基态磁矩及自由能的理论公式,重点考察了单轴各向异性场D和横场Ω对自旋系统基态磁化曲线及自由能的影响,并且从磁化曲线可观察系统一阶、二阶相变的特征。研究发现随着单轴各向异性场和横场的变化,磁化曲线可分成3种:系统的磁矩由2跃变到1,发生一阶有序-有序相变;系统的磁矩由2或1跃变到0,发生一阶有序-无序相变;系统的磁矩由2或1平滑地变化到0,发生二阶有序-无序相变。在m-D/(zJ)基态磁化曲线中随着Ω的增加,系统的磁矩由2到1,1到0的一阶相变现象相继消失;同样在m-Ω/(zJ)基态磁化曲线中随着D的增加,也相继消失。通过对基态自由能曲线的分析还发现当Ω增加或D增加时,自由能总是呈下降的趋势。     

高粘度磁性液体的制备研究

采用直流电弧等离子体法 ,分别在 1个大气压的H2 +Ar和CH4+He混和气氛中制备了Fe、Ni、Fe-Ni合金磁性超微粒子 (UFP)。利用Fe、Ni、Fe-Ni合金超微粒子 ,选择适当的表面活性剂和载液 ,制备了高粘度磁性液体(ML) ,常温 (2 5℃ )粘度为 (2 6～ 6 0 )× 10 5mPa·s,高温 (85℃ )粘度为 (1 0～ 3 2 )× 10 5mPa·s,室温下饱和磁化强度为FeML 2 4 0 8～ 6 8 0 0Am2 /kg,NiML 10 19～ 17 83Am2 /kg,Fe-NiML 2 6 2 1～ 75 13Am2 /kg     

基片对间接耦合式超磁致伸缩薄膜静态磁化性能的影响

间接耦合式超磁致伸缩薄膜是一种新兴的具有优异机械物理性能的功能材料，已成为微型器件材料研究的热点之一。由于是在弹性基片上通过物理沉积方法得到该种薄膜材料，因此基片的物理性能对薄膜材料的磁化性能会产生重要影响。通过对物理性能差异较大的铜、聚酰亚胺两种基片的间接耦合式超磁致伸缩薄膜的磁化曲线、饱和磁化强度等进行实验研究与分析比较，得到不同物理性能基片对超磁致伸缩薄膜特性的影响规律，为进一步制备性能各异的薄膜材料奠定基础。     

Influence of calcination rate on morphologies and magnetic properties of MnFe2O4 nanofibers

In the present study, we succesfully synthesized electrospun MnFe₂O₄ nanofibers (NFs) from poly(N-vinylpyrrolidone)/manganese(II) nitrate composite by electrospinning and then as-spun NFs were calcined 450 °C for 2 h in air atmosphere to remove the polymer matrix and fabricate inorganic MnFe₂O₄ nanofibers. In order to investigate the sintering behavior of MnFe₂O₄ nanofibers in air atmosphere, the synthesized as-spun nanofibers were calcined with different calcination rates. Thus the effect of calcination rate on structure and morphology of nanofibers were discussed clearly. The structural, magnetic, morphological, spectroscopic and thermal characterizations were also done by XRD, VSM, TEM, SEM, FTIR and TG analysis. In the presence of slow calcination rate, only peaks of MnFe₂O₄ could be observed on other hand in the presence of rapid calcination rate, formation of an impurity was observed. Scanning electron microscope images revealed that MnFe₂O₄ nanorods possess a broader range size distribution with higher particle size. Also, magnetic properties were both size and shape dependent.     

An fully-automated measurement system for identifying magnetization characteristics of switched reluctance motors

Precise understanding of knowledge and behavior of the SRM is needed for the development and verification of advanced control algorithm. An fully-automated measurement system is proposed in this paper to identify the magnetization characteristics of the SRM as functions of the winding current and rotor position. The proposed system can characterize the SRM automatically and take magnetic nonlinearity and static iron losses into account. The post-mortem data processing with a graphical user interface constitutes the measuring procedures and provides easy manipulation and clear presentation of the results. The theoretical sensitivity is derived; error sources and uncertainties of the measurement are also analyzed and discussed. Experimental results with good accuracy conducted on a four-phase SRM show the correctness and practicability of the presented system. Special emphasis is oriented on the suitability for the production line application to on-line determine the saturation behaviors of the SRMs.