Dissertation > Mathematical sciences and chemical > Physics > Condensed Matter Physics

Nd-Fe-B Based Nanocomposite Magnets and Their Coercivities

Author LiZhuBai
Tutor LiuXinCai
School Ningbo University
Course Condensed Matter Physics
Keywords Nanocomposite magnets Rapid quenching High energy ball milling Hot pressing Thermodynamic properties of Coercivity Exchange coupling
CLC O469
Type Master's thesis
Year 2010
Downloads 58
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In this paper, the melt-spinning, high-energy ball milling, hot-pressing method of preparation of nanocomposite magnets (Nd 10.5 the Pr 2.5 ) the Fe 80 Nb < sub> 1 B 6 / FeCo, magnet soft phase mass percentage relationship between grain size and magnetic properties, the thermodynamic properties of phase change of the crystallization process, the magnetization reversal process nucleation are analyzed and discussed from pinning effect, as well as the weak exchange coupling. High energy ball milling the powder particles refinement and uniformity, to increase the energy of the system at the same time, improve the nucleation rate of crystallization in the crystallization process, hot press also has a role in improving the nucleation rate of crystallization and inhibit long-range diffusion of atoms, These two finer the grain, the grain size distribution is more concentrated. Although the high-energy ball milling pressing nanocrystalline (Nd 10.5 Pr 2.5 ) Fe 80 Nb 1 B 6 the exchange coupling between the single-phase magnet grains stronger effect to some extent so that the decline in the coercive force of the magnet, but the grain size of the magnet is concentrated distribution, grain boundary is relatively large, the magnet can maintain a high coercivity coercivity reached 1631kA / m, and without high energy ball milling hot pressing (Nd 10.5 Pr 2.5 ) Fe 80 Nb 1 B 6 coercivity magnet 1616kA / m fairly. With the (Nd 10.5 Pr 2.5 ) Fe 80 Nb 1 B 6 / FeCo composite magnet FeCo mass percentage increases, the saturation magnetization of the magnet increased, the coercivity decreased. Discussion and analysis, (Nd 10.5 Pr 2.5 ) Fe 80 Nb 1 B 6 / FeCo nano composite magnet is less than 20% percent by mass of the soft magnetic phase, the magnetization reversal process of self-pinned more prominent, the composite magnetic coercive force is high, the mass percentage of FeCo 10% and 20%, ( Nd 10.5 Pr 2.5 ) Fe 80 Nb 1 B 6 / FeCo composite magnet the coercivity, respectively 1357kA / m and 801kA / m; magnetic dipole interaction is more prominent when the quality of the soft magnetic phase percentage greater than 30%, the magnetization reversal process mainly in the soft phase intragranular nucleation mechanism composite magnetic coercivity low the When the FeCo mass percentage is 40%, the coercive force of the composite magnet is only (Nd 10.5 ) Fe Pr 2.5 80 Nb 1 B 6 single phase magnet of 9.1%. Composite magnetic soft magnetic phase of α-Fe crystal grain size is too large, than the hard magnetic phase in between 40nm 7 0nm Nd 2 Fe 14 B grain size, this due to Nd the 2 Fe B and α-Fe 14 thermodynamic phase transition from amorphous to nanocrystalline characteristic differences decide , α-Fe before of Nd 2 the of Fe 14 B-shaped nuclear crystallization, resulting in a long time, the grain growth of α-Fe, the relatively large grain size, which is also composite a major cause of low coercive force of the magnet. The soft nano composite magnet of Nd-Fe-B, the vicinity of the grain boundary of the hard magnetic phase defects will weaken the exchange coupling interaction between the grains, resulting in decline in the composite magnetic coercivity. Fundamentally improve the magnetic properties of nanocomposite magnets should explore new ways to weaken the Nd 2 Fe 14 B and α-Fe phase change process thermodynamic properties of difference the influence of the grain size of the composite magnet, control of the grain size of the soft magnetic phase of α-Fe in the range of less than the grain size of the hard magnetic phase, while reducing the atomic vacancy defects such as the interface between the grains.

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