The magnetic anisotropy of Fe 25 Ni 75 nanocrystallites in the range of 10～20 nm was measured by the law of approach to saturation. The samples were prepared by mechanical alloying process, and the average ...The magnetic anisotropy of Fe 25 Ni 75 nanocrystallites in the range of 10～20 nm was measured by the law of approach to saturation. The samples were prepared by mechanical alloying process, and the average crystal size was determined by X ray diffraction. The effective magnetic anisotropy of these fine particles is found in an order of 10 6 erg/cm 3 that is much greater than that of normal crystal size of particles. The dependence of magnetic anisotropy on the particle size was studied. It has been demonstrated that the strain anisotropy occupies the most of the total magnetic anisotropy, and the internal strain is a critical factor for their magnetic properties.展开更多
YBCO bulk superconductors were prepared by the solid state reaction andtop-seed-melt-textured growth (TSMTG) process. By using the AC susceptibility measurement, thecritical transition temperature T_c of samples is 91...YBCO bulk superconductors were prepared by the solid state reaction andtop-seed-melt-textured growth (TSMTG) process. By using the AC susceptibility measurement, thecritical transition temperature T_c of samples is 91.5 K for the highest value, and the transitionwidth ΔT_c is less than 1 K. The highest magnetization critical current densities J_c achieved 10~6A/cm^2 under 5 T at 10 K and 1.35X10^4 A/cm^2 under 2 T at 70 K (H//c), respectively. The resultscombining the SEM observation indicate that doping of Y211 particles is more effective in improvingthe growth quality of melt-textured YBCO superconductor and in reducing the micro-cracks ofspecimens. Doping of Y_2O_3 powder forms the rod-shaped Y211 particles, but doping of Y211 particlesdirectly to matrix materials forms the spherical Y211 particles mainly. Combining themicrostructures with J_c measurements shows that the interfaces are most important on flux bundlepinning, in which the gradient of free energy is larger than that of other place between the Y211particles and the Y123 matrix materials.展开更多
I. INTRODUCTIONThe outstanding magnetic properties of Nd-Fe-B permanent alloy with very high coercive force and maximum magnetic energy product have attracted scientists’ attention greatly and extensive investigation...I. INTRODUCTIONThe outstanding magnetic properties of Nd-Fe-B permanent alloy with very high coercive force and maximum magnetic energy product have attracted scientists’ attention greatly and extensive investigation has been made on its structure and mag-展开更多
The aim of this work was to investigate the size-related magnetism for the single-domain Co Fe2O4 nano-particles synthesized using the hydrothermal method. The effects of the reaction temperature and the reaction time...The aim of this work was to investigate the size-related magnetism for the single-domain Co Fe2O4 nano-particles synthesized using the hydrothermal method. The effects of the reaction temperature and the reaction time on the lattice constants, particle morphologies, and the room-temperature magnetic properties were studied from the X-ray diffraction, the transmission electron microscope, and the vibrating-sample magnetometer. The experimental results show that the samples are composed of Co Fe2O4 nano-particles with an average crystallite size（D） smaller than 40 nm, and the magnetic properties of the samples can be manipulated in a wide range： the MS values vary from smaller than 50 emu/g to close to 80 emu/g, and the HC values are between about 200 Oe and 2000 Oe. Additionally, the relationship between HC and 1/D^3/2 satisfi es linearship, showing the characteristic of single-domain structure. These results indicate that the single-domain Co Fe2O4 nano-particles with size controlled between the superparamagnetic critical size and single-domain critical size can be easily prepared using this hydrothermal method.展开更多
文摘The magnetic anisotropy of Fe 25 Ni 75 nanocrystallites in the range of 10～20 nm was measured by the law of approach to saturation. The samples were prepared by mechanical alloying process, and the average crystal size was determined by X ray diffraction. The effective magnetic anisotropy of these fine particles is found in an order of 10 6 erg/cm 3 that is much greater than that of normal crystal size of particles. The dependence of magnetic anisotropy on the particle size was studied. It has been demonstrated that the strain anisotropy occupies the most of the total magnetic anisotropy, and the internal strain is a critical factor for their magnetic properties.
文摘YBCO bulk superconductors were prepared by the solid state reaction andtop-seed-melt-textured growth (TSMTG) process. By using the AC susceptibility measurement, thecritical transition temperature T_c of samples is 91.5 K for the highest value, and the transitionwidth ΔT_c is less than 1 K. The highest magnetization critical current densities J_c achieved 10~6A/cm^2 under 5 T at 10 K and 1.35X10^4 A/cm^2 under 2 T at 70 K (H//c), respectively. The resultscombining the SEM observation indicate that doping of Y211 particles is more effective in improvingthe growth quality of melt-textured YBCO superconductor and in reducing the micro-cracks ofspecimens. Doping of Y_2O_3 powder forms the rod-shaped Y211 particles, but doping of Y211 particlesdirectly to matrix materials forms the spherical Y211 particles mainly. Combining themicrostructures with J_c measurements shows that the interfaces are most important on flux bundlepinning, in which the gradient of free energy is larger than that of other place between the Y211particles and the Y123 matrix materials.
文摘I. INTRODUCTIONThe outstanding magnetic properties of Nd-Fe-B permanent alloy with very high coercive force and maximum magnetic energy product have attracted scientists’ attention greatly and extensive investigation has been made on its structure and mag-
基金Funded by the National Natural Science Foundation of China(51172166)the PhD Programs Foundation of City College,Wuhan University of Science and Technology(2014CYBSKY003)
文摘The aim of this work was to investigate the size-related magnetism for the single-domain Co Fe2O4 nano-particles synthesized using the hydrothermal method. The effects of the reaction temperature and the reaction time on the lattice constants, particle morphologies, and the room-temperature magnetic properties were studied from the X-ray diffraction, the transmission electron microscope, and the vibrating-sample magnetometer. The experimental results show that the samples are composed of Co Fe2O4 nano-particles with an average crystallite size（D） smaller than 40 nm, and the magnetic properties of the samples can be manipulated in a wide range： the MS values vary from smaller than 50 emu/g to close to 80 emu/g, and the HC values are between about 200 Oe and 2000 Oe. Additionally, the relationship between HC and 1/D^3/2 satisfi es linearship, showing the characteristic of single-domain structure. These results indicate that the single-domain Co Fe2O4 nano-particles with size controlled between the superparamagnetic critical size and single-domain critical size can be easily prepared using this hydrothermal method.
