Curie Temperature Measurement Of A Double-phase Rare Earth Permanent Magnet

Temperature stability of the magnetic materials for its practical application has important significance, Curie temperature is one of the main factors which influence the temperature stability, and the measurement is the basis of the Curie temperature, so looking for a simple, accurate and low cost Curie temperature measuring method is very significant. The thesis regards the doublephase(Nd,Pr)12.8Dy0.2Fe77.4Co4B5.6 alloy as the object of research, using DSC to measure the Curie temperature of hard magnetic phase, and made a comparison with PPMS measured values.First, using PPMS to measure M-T curve of(Nd,Pr)12.8Dy0.2Fe77.4Co4B5.6 ingot casting alloy, a maximum of dM/dT absolute value 637.0 K was defined as the Curie temperature of(Nd,Pr,Dy)2(Fe,Co)14B phase. The heating and cooling curves of the alloy under the rate of 3K/min, 10K/min, 20K/min, 30K/min and 40K/min was obtained by high temperature DSC. The initial point, peak and ending points of characteristic peak of(Nd,Pr,Dy)2(Fe,Co)14B phase were found, then characteristics equations were obtained by least square fitting. Comparing 3K/min calculated values with PPMS measured value, the results showed that 3K/min calculated value of the peak fitting line in DSC cooling curve which was 638.7K had a low relative error 0.27% with the PPMS measurement value 637.0 K. This method had high accuracy.Heating and cooling curves of pure Fe powder with a high Curie temperature were measured by DSC under different rate, 3K/min calculated values were obtained, then made some comparison with the standard value in CINDAS material performance database. It was found that for high Curie temperature measurement, the fitting line 3K/min calculated value of peak temperature in cooling curve which was 1042.7K was more accurately, and the relative error with standard value which was 1042 K was 0.07%. So DSC measurement for high Curie temperature still had high accuracy.Use the same method to get the Curie temperature of α-(Fe,Co,Nd) soft magnetic phase in(Nd,Pr)12.8Dy0.2Fe77.4Co4B5.6 ingot, and the value was 1083.0K. After a heat treatment at 873 K for 10 hours, the Curie temperature value was 1066.3 K, which was 16.7K lower than the ingot alloy. Analysis result showed that the main reason was that the Co content in α-(Fe,Co,Nd) reduced. The influence of equivalent heat treatment time on the Curie temperature of α-(Fe,Co,Nd) was also discussed. After heat treatment, the Curie temperature of(Nd,Pr,Dy)2(Fe,Co)14B hard magnetic phase increased from 638.7 K to 642.3 K. Combined with XRD and energy spectrum analysis, the main reason for the rise of the Curie temperature was the Co content in(Nd,Pr,Dy)2(Fe,Co)14B phase increased. Co entered the 2:14:1 phase and replaced part of Fe atoms, hence the total exchange integral increased and a higher Curie temperature was obtained.