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

The structural and magnetic properties of Pr ₁₃Fe _{82- x}Mn _xB ₅ 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.