No abstract

To improve the coercivity of the Nd-Fe-B sintered magnets, the Cu29.8Al70.2 (at.%) powders with low melting point were introduced into the Nd-Fe-B magnets. The magnetic properties, microstructure, thermal stability and corrosion behavior of the sintered magnets with different amount of Cu29.8Al70.2 (0,0.25,0.50,0.75,1.0 wt.%) were investigated. When the amount of doped Cu29.8Al70.2 was less than 0.75 wt.%, the coercivity was improved, especially that of the magnets with 0.25 wt.% Cu29.8Al70.2, markedly increased to 13.97 kOe from 12.67 kOe (without CuAl). The improvement of magnetic properties could be attributed to enhanced wettability between Nd2Fe14B phase and Nd-rich phase and decreased exchange coupling between grains, which depended on the optimization of grain boundary microstructure and their distribution by codoping Cu and Al. With the addition of 0-1.0 wt.% Cu29.8Al70.2 powders, the reversible temperature coefficients of remanence and coercivity of the magnets could be also improved. The corrosion resistances was also found to be improved through small addition of Cu29.8Al70.2 powder in 3.5 wt.% NaCl solution by electrochemical and immersion tests, which could be due to the enhancement of the Nd-rich intergranular phase by addition Cu29.8Al70.2.

In this paper, we report on the structural, magnetic and magnetocaloric properties of La 0.8 K 0.2 MnO 3 manganites annealed at different temperatures in the form of powder. The analyses of X-ray diffraction patterns indicate that the crystallographic structure is unchanged when the annealing temperature increases from 800 to 1200 • C. The annealing conditions have obvious influences on the Curie temperature and isothermal entropy change. With an applied field change of 5 T, the maximum values of isothermal entropy changes are found to be 3.7 J/kg K at 283 K, 3.4 J/kg K at 298 K, 4.0 J/kg K at 308 K, 4.3 J/kg K at 318 K, and 4.6 J/kg K at 293 K for T a = 800, 900, 1000, 1100, and 1200 • C, respectively. The results imply that the change of annealing conditions is an applicable way for optimizing the Curie temperature and magnetocaloric effect for such potassium-doped manganites.

No abstract

In this paper we report on the structural, magnetic and magnetocaloric properties of La 0.67 Sr 0.33-x Mg x MnO 3 (x = 0, 0.05, 0.15 and 0.2) manganites synthesized by sol-gel method. The Mg-doping does not modify the crystal structure of the undoped manganite, but results in a slightly change of the lattice parameters. Both Curie temperature and saturation magnetization decrease with increasing Mg content. With a field change of 5 T, the maximum values of isothermal entropy change are found to be 2.49, 1.28, 1.37 and 1.30 J/kg·K for x = 0, 0.05, 0.15 and 0.2, respectively. The Mg-doped manganites exhibit stable MCE in a wide temperature range from ~50 K to ~300 K, which is important to the magnetic refrigeration.M 0018-9464 (c)lattice parameters are slightly modified by the Mg-doping. With the increasing Mg content, the Curie temperature and saturation magnetization decrease. The MCE peak is lowered and broadened by the Mg-doping. The maximum values of -ΔS T under a magnetic field change of 5 T are found to be 2.49, 1.28, 1.37 and 1.30 J/kg·K for x = 0, 0.05, 0.15 and 0.2, respectively.