Effect of Chromium Substitution for Iron on the Magnetic and Structural Properties of (TmxPr1– x)2Fe17

The (Tm x Pr 1 – x ) 2 Fe 17 and (Tm x Pr 1 – x ) 2 Fe 16.5 Cr 0.5 compounds crystallize with the formation of the rhombohedral Th 2 Zn 17 -type structure for the compositions with x = 0–0.4 and the hexagonal Th 2 Ni 17 -type structure for the compositions with x = 0.8–1 and x = 0.75–1, respectively. Both structures coexist in the (Tm x Pr 1 – x ) 2 Fe 17 and (Tm x Pr 1 – x ) 2 Fe 16.5 Cr 0.5 compounds with x = 0.5–0.75 and x = 0.5–0.6, respectively. The (Tm x Pr 1 – x ) 2 Fe 17 compositions with 0 < x < 0.6 are ferrimagnets; at x = 0.6–1, additionally a high-temperature helical magnetic state is realized. The substitution of chromium for iron leads to the transformation of the helimagnet to ferrimagnet; in this case, the difference between the Curie temperatures of rhombohedral and hexagonal phases is unexpectedly high (25–28 К). For the composition with x = 0.8, the Curie and Néel temperatures and the ferrimagnet–helimagnet transformation temperature are minimum, and the microdeformations are maximum. The overlap of two peaks in –Δ S M ( T ), which correspond to the magnetic entropy change at two magnetic phase transformation temperatures, favors the realization of the higher cooling capacity of the two-phase compositions as compared to that of neighboring single-phase compositions.