Magnetic hardening in Mn-substituted Pr-Fe-B alloys at cryogenic temperatures

The structural and magnetic properties of Pr13Fe82-xMnxB5 alloys have been studied in a wide temperature range. X-ray diffraction data showed the presence of 2:14:1 phase in all the samples. A maximum coercivity of 30 kOe at 10 K was observed in a sample containing 22% Mn, which dropped rapidly to a value of 8 kOe at 40 K and was negligible at temperatures above 120 K. The coercivity of the Mn-free sample was less than 1 kOe at 10 K. The Curie temperature of the alloys dropped drastically with Mn substitution from 580 to 120 K for the x=30 sample. Initial magnetization data showed a domain wall pinning like behavior. It is suggested that this domain wall pinning occurs at atomic size defects because of the extremely thin size of domain walls in these alloys. (orig.)