Pinning-controlled magnets

Fig. 15. Schematic magnetization curves for nucleation controlled magnets, type A, like SmCo5 and for pinning controlled magnets, type B, like Sm(Co, Cu, TM)X.

Most experimental observations made on the Nd-Fe-B type materials indicate that the coercivity in the corresponding sintered magnets is nucleation-controlled (fig. 47a or b) rather than pinning controlled (fig. 47c). 

Fig. 16. Comparison of the virgin magnetization curves for typical magnets of three basic behavior types A is nucleation controlled B is pinning controlled, and C is mixed (or pinning with very nonuniform pin...

The first flight of the Reel Down system took place on 15 September 1982 from the National Scientific Balloon Facility in Palestine, Texas. When the balloon was properly positioned for the descent phase of the experiments, a pin locking the suspended instrument cluster to the winching system was pulled and the controlled descent phase was initiated by releasing a magnetically controlled brake. Descent velocity was selectable by command from the ground. A line velocity of 7 1 m/sec was used for the experiment reported here. A full treatment of mechanical and electronic systems, as well as the data analysis regarding the dynamics of the system, appears elsewhere [19]. 

Fig. 15. Coercivity versus maximum applied field at r = 200K for a NdFeB (20nm)/Fe(0.5nm) sample. The result indicates that magnetization reversal in the easy direction is controlled by a domain-wall pinning mechanism. (By courtesy of Dr. D. Sellmyer, Behlen Lal5. of Physics, Univ. Nebraska, Lincoln, NB, USA).

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