Structure, phase transformation, and magnetic properties of SmCo7-xCrx magnets

SmCo7-xCrx (x=0-0.6) magnets have been synthesized by mechanical alloying and subsequent annealing. A small amount of Cr favors the formation of Th2Ni17-type 2:17 phase and increasing the Cr content can extend the temperature range in which the hexagonal 2:17 phase remains stable. The coercivities of the SmCo7-xCrx magnets are significantly enhanced by increasing the Cr content. The highest coercivity of 15.8 kOe is obtained for the SmCo6.4Cr0.6 alloy annealed at 700 degrees C for 30 min. The transformation of Th2Ni17-type structure to Th2Zn17-type structure is observed when increasing the annealing temperature. The magnetization reversal process of the alloys has been discussed, according to the measurement of initial magnetization curves and minor hysteresis loops.