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The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73±0.15)μB/f.u., which is ∼70% of that for the bulk-like Fe3O4. A significant unquenched orbital moment up to 0.5460.05lB/f.u. was observed, which could come from the symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will add capacities to the Fe3O4-based spintronics devices in the magnetization reversal by the electric field. [ABSTRACT FROM AUTHOR]

Nd-Fe-B permanent magnets with a small amount of CuZn5 powders doping were prepared by conventional sintered method. The effects of CuZn5 contents on magnetic properties and microstructure, electrochemical corrosion resistance of sintered Nd-Fe-B magnets were systematically studied. The results show that the magnetic properties of magnets do not have a significant variation by CuZn5 powders doping; the coercivity of magnets rises gradually, while the remanence of the magnets decreases a little with increasing of the CuZn5 amount. The CuZn5 doped magnets have more positive corrosion potential, Ecorr, and much lower corrosion current density, icorr, than the magnets without CuZn5 doping, indicating CuZn5 doping could improve the corrosion resistance. Both Zn and Cu enrich mainly into the Nd-rich phase, fully improve the wettability between the Nd-rich phase and the Nd2Fe14B phase, and repair the defects of the main phase, so the coercivity of magnets doped with CuZn5 powders rises. Such microstructure modification effectively restrains the aggressive inter-granular corrosion. As a result, the CuZn5 doped magnet possesses excellent corrosion resistance in NaCl electrolyte. [ABSTRACT FROM AUTHOR]

Anisotropic MnBi/SmFeN (MnBi=0, 20, 40, 60, 80, and 100 wt. %) hybrid bonded magnets were prepared using MnBi powders and commercial SmFeN powders. With the increase in MnBi content from 0 to 100 wt. %, the density of the hybrid magnets improves linearly from 4.27 g/cm3 to 6.3 g/cm3, while the coercivity of the hybrid magnets does not change much at 293 K. For the pure MnBi magnet, the coercivity is increased from 10.76 kOe at 293K to 16.5 kOe at 373 K. For the hybrid magnet with 40 wt. % MnBi, the coercivity is increased by 19% compared to pure SmFeN magnet at 373 K. In the temperature range of 293 K-373 K, the coercivity temperature coefficient of the hybrid magnets changes gradually from -0.42%/K for the pure SmFeN magnet to -0.11%/K for the magnet with 80 wt. % MnBi, and becomes 0.67%/K for the pure MnBi magnet. [ABSTRACT FROM AUTHOR]

In this paper, we studied the magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted high energy ball milling. The hysteresis loop with the initial magnetization curve and the corresponding differential susceptibility curve of thermally demagnetized SmCo6.6Nb0.4 nanoflakes were studied. It is concluded that the magnetization reversal process of the specimen is determined by domain wall motion, i.e., the magnetic hardening mechanism of the magnetic powders is dominated by domain wall pinning. Moreover, the dependence of coercive field of the nanoflakes on the maximum applied field derived from minor hysteresis loops also confirms the pinning effect in the magnetization reversal. [ABSTRACT FROM AUTHOR]

Spark plasma sintering technique had been applied to prepare bulk isotropic and anisotropic nanostructured Nd-Fe-B permanent magnets via hot pressing and subsequent hot deformation process. Influences of processing conditions and deformation height reduction on the structure and magnetic properties of the magnets were investigated. For the hot deformed magnet with 80% height reduction, XRD patterns of the anisotropic magnets show dominant (00l) diffraction peaks indicating evident c-axis crystallographic alignment in the magnet. Under the optimal processing conditions, the anisotropic magnet with 80% height reduction exhibits excellent magnetic properties as remanence (Br) of 1.492 T, coercive force (Hci) of 1004 kA/m, and the maximum energy product [(BH)max] of 400 kJ/m3, which are among the highest reported magnetic properties of nanostructured Nd-Fe-B permanent magnets. [ABSTRACT FROM AUTHOR]

Structure and magnetic properties were studied for Tm2(Co1-xFex)17 bulk nanocrystalline magnet synthesized by spark plasma sintering technique. X-ray diffraction results indicate both ingot and sintered magnet of Tm2(Co0.7Fe0.3)17 alloy exhibit hexagonal Th2Ni17 type structure. The microstructure of the magnet is composed of Th2Ni17 type nanograins with an average size of 35 nm detected by transmission electron microscopy and selected area electron diffraction patterns. Magnetic measurement shows that the remanence of the magnet is higher at 573 K than at 300 K, indicating there is a positive remanence temperature coefficient in the magnet. The anisotropy field of Tm2(Co0.7Fe0.3)17 alloy is 3.8 T, which is much higher than the HA of 2.3 T for the pure Tm2Co17alloy. The coercivity of the sintered magnet increases from 0.25 to 0.354 T after optimal annealing. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties were studied for bulk nanocrystalline SmCo5 sintered magnet produced by spark plasma sintering technique. X-ray diffraction patterns show that the sintered magnet exhibits CaCu5 crystal structures. Transmission electron microscopy (TEM) observation indicates the average grain size of the magnet of about 40 nm. Magnetic measurement shows that the coercivity reaches as high as 2.85 T; the saturation magnetization and the remanence are 0.71 and 0.5 T, respectively. The magnet exhibits good thermal stability with a coercivity of 0.9 T at 773 K and a coercivity coefficientβ of -0.15%/K. [ABSTRACT FROM AUTHOR]

Polarization curve and electrochemical impedance spectroscopy tests have been applied to investigate the corrosion kinetics for both spark plasma sintered (SPS) and conventional sintered Nd–Fe–B magnets in different electrolytes. Effect of microstructure modification on the chemical stability of the magnets was discussed. Both magnets exhibit evident passive behavior in alkaline electrolyte but are susceptible to corrosion in weak acid and saline electrolytes. SPS magnets are more corrosion resistant than conventional sintered magnets due to a remarkable microstructure modification formed in the SPS process. Further investigation shows that the unique microstructure in SPS magnets effectively restrains the aggressive intergranular corrosion which takes place along Nd-rich phases in conventional magnets. [ABSTRACT FROM AUTHOR]

Oxidation kinetics of Nd–Fe–B permanent magnets prepared by both spark plasma sintering (SPS) and conventional sintering techniques has been studied at elevated temperature in dry air environment. Compared with the conventional sintered magnet, the SPS magnet possesses much lower oxidation rate, which leads to less reduction of magnetic properties of the SPS magnet than that of the conventional sintered magnet. Microstructure observation shows that the SPS magnet possesses unique microstructure due to the special sintering mechanism of SPS technique. In detail, the grain size of the Nd2Fe14B main phase is fine and uniform, only a few Nd-rich phases form along the grain boundaries of Nd2Fe14B phase, while most of them agglomerate into triple junctions as small particles. Such microstructure modification restrains effectively the intergranular corrosion along Nd-rich phase in the SPS magnet. As a result, the SPS magnet possesses excellent corrosion resistance at elevated temperature. [ABSTRACT FROM AUTHOR]

Chemical coating, hot compaction, and hot deformation techniques have been applied to prepare bulk isotropic and anisotropic Nd2Fe14B/α-Fe nanocomposite magnets. The effect of α-Fe content on the structure and magnetic properties of the magnets were studied. For the isotropic magnets, the remanence (Br) increases as the α-Fe content increases, while the coercive force (Hci) drops simultaneously. For the anisotropic magnets, the Br rises first, peaking at 2 vol % of α-Fe content, then falls as the α-Fe content increases, and Hci drops significantly for all the α-Fe containing anisotropic magnets. Crystal structure analysis shows that only the magnets with no more than 2 vol % α-Fe exhibit strong c-axis crystal texture of Nd2Fe14B phase after deformation. Microstructure observation also shows that there are many Nd2Fe14B equiaxial grains even after hot deformation in the magnets with α-Fe more than 2 vol %. [ABSTRACT FROM AUTHOR]

Bulk anisotropic nanocrystalline SmCo5 magnets have been prepared by hot deformation method. The height reduction of the magnets plays a key role in inducing the crystallographic alignment in the magnet. Increase of height reduction to 90% leads to the formation of platelet shape grains perpendicular to the press direction; correspondingly c-axis crystallographic texture and magnetic anisotropy were developed in the deformed magnets. The coercivity of the magnets increases first,and then decreases again with the increase of the height reduction. The magnet with 70% height reduction exhibits a high coercivity over 5 T. [ABSTRACT FROM AUTHOR]