Search

Abstract: Effect of Ga content on the phase constitution, magnetic phase transition temperatures (T C), and exchange bias (EB) behaviors of Fe50Mn24+ x Ga26− x (x =0, 0.5, 1, 3) as-spun ribbons have been investigated. Fe50Mn24Ga26 ribbon exhibits a magnetic phase transition of B2-type structure from FM to PM state at T C1 =190K. Another magnetic phase transition of face-center-cubic structure from AFM to FM takes place at T C2 =240K for Fe50Mn25Ga25 sample. The values of exchange bias field (H E) at 10K after field-cooling (FC) at 30kOe from 300K are 14, 41, 1886, 1740Oe, respectively, as x is increased from 0 to 3. The phenomena are attributed to the change of exchange interactions at FM/AFM interfaces due to the change of proportion of FM and AFM phases in low temperature magnetic states. The maximum exchange bias field H E =2.4kOe at 10K after field-cooling at 40kOe is observed for Fe50Mn25Ga25. [Copyright &y& Elsevier]

Magnetic properties of the anisotropic NdFeB magnets prepared by hot pressing followed by die-upsetting NdFeB MQU-F powders doped with low-melting RCu alloy powders were explored, where RCu stands for Nd 70 Cu 30 , Dy 70 Cu 30 and (Nd 0.5 Dy 0.5 ) 70 Cu 30 , respectively. In addition, the post-annealing at 600 °C was employed to modify the microstructures and the magnetic properties of the hot deformed magnets. It is found that doping RCu alloy powders is effective in enhancing the coercivity of the hot deformed NdFeB magnets from 15.1 kOe to 16.3–19.5 kOe. For Nd 70 Cu 30 -doped magnets, the increment of coercivity is only 1.2 kOe. Meanwhile, Dy 70 Cu 30 -doped and (Nd 0.5 Dy 0.5 ) 70 Cu 30 -doped magnets show an almost identical enhancement of coercivity of about 4.4 kOe. Importantly, the latter magnet shows a beneficial effect of reducing the usage of Dy from 1.6 wt% to 0.8 wt%. TEM analysis shows that nonmagnetic Nd, Dy and Cu appear at grain boundary and isolate the magnetic grains, leading to an enhancement of coercivity. Doping lower melting point Dy-lean (Nd 0.5 Dy 0.5 ) 70 Cu 30 powders into commercial MQU-F powders for making high coercivity hot deformed NdFeB magnets might be a potential and economic way for mass production. [ABSTRACT FROM AUTHOR]

Magnetic properties of melt spun Co 86.5 Hf 10.5 MB 2 ribbons with refractory elements substitution (M=Cr, Nb, Ti, Zr) have been studied. For ternary Co 86.5 Hf 11.5 B 2 ribbon, permanent magnetic properties of B r =0.71 T, i H c =192 kA/m, and (BH) max =34.4 kJ/m 3 are obtained, and they are significantly improved to B r =0.73–0.76 T, i H c =136–216 kA/m and (BH) max =38.4–52.8 kJ/m 3 with M substitution. Summarized with the results of x-ray diffraction refinement, thermal magnetic analysis, and transmission electron microscopy, the Co 86.5 Hf 10.5 MB 2 nanocomposites following the optimal crystallization treatment mainly consist of orthorhombic 7:1 and face-center-cubic Co phases. Fine microstructure with average grain size in the range of 12.5−19.6 nm promotes exchange coupling effect between magnetic grains, thus improving permanent magnetic properties. The magnetic field dependence of coercivity reveals that coercivity of the studied Co 86.5 Hf 10.5 MB 2 nonocomposites is mainly governed by the reverse domain nucleation mechanism. [ABSTRACT FROM AUTHOR]

Highlights: [•] The melt-spun and annealed Mn1−x Cu x CoGe ribbons are prepared. [•] A single FOMST with gaint MCE near RT is achieved in annealed Mn1−x Cu x CoGe (x =0.02, 0.04) ribbons. [•] A large enhancement of −ΔS m peak values from the melt-spun to annealed ribbons is obtained. [ABSTRACT FROM AUTHOR]

Abstract: The melt-spun MnV0.02CoGe0.99 ribbons were successfully prepared and the microstructure, magnetic and magnetocaloric properties of these ribbons were investigated. A single phase with the hexagonal Ni2In-type structure was confirmed by XRD methodology at room temperature. In these ribbons, a ferromagnetic phase transition (~252K) with the second-order nature was observed accompanied by an abrupt change of magnetization, which induces moderate values of magnetic entropy change and relative cooling power, 0.9J/kgK and 36J/kg, respectively, in the magnetic field change of ΔH=10kOe. The appreciable magnetocaloric effect with an excellent thermal/magnetic reversibility as well as more economical would make these ribbons materials suitable as a magnetic refrigerant. [Copyright &y& Elsevier]

Abstract: Cylindrical Nd9.5Febal.Co x Nb2.5Zr0.5B15 (x =0, 10, 20) magnets with diameter of 0.9–1.5mm have been prepared by directly casting method. TMA and DSC analysis show that doping Co may enhance the glass forming ability and refine the grain size of the directly cast magnets effectively. Nevertheless, the amorphous phase is easily to appear at the peripheral region but not at the interior region, leading to much inhomogeneous microstructure especially when too high Co content (x =20) is added. Magnetic measurements show that higher maximum energy product and coercivity can only be obtained in Co-free magnets with smaller diameter (⩽0.9mm), while higher maximum energy product and coercivity could be appeared in Co-doped magnets (x =10) with larger diameter (1.1–1.3mm in diameter). [Copyright &y& Elsevier]

Effect of Ca substitution on the multiferroic properties of non-epitaxially grown polycrystalline Bi 1− x Ca x FeO 3 (BCFO) films on refined Pt(1 1 1) electrode buffered glass substrates is studied. The structural analysis shows that a pure perovskite phase with isotropic orientation is present for BCFO films ( x = 0.05–0.15). The grain size and surface roughness are reduced with increasing x . Different from the BCFO ceramics, good ferroelectric properties with the remanent polarization (2 P r ) of 91–124 μC/cm 2 and electrical coercive field ( E c ) of 294–394 kV/cm are obtained in BCFO polycrystalline thin films. Furthermore, the substitution of Ca 2+ for Bi 3+ effectively enhance the ferromagnetic properties with magnetization ( M s ) of 5.9–8.2 emu/cm 3 and coercivity ( H c ) of 1224–1258 Oe. The ferromagnetic and ferroelectric properties and leakage behavior as functions of Ca content x are discussed. [ABSTRACT FROM AUTHOR]