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

Resumo

The (Tm_xPr_1 – x)₂Fe₁₇ and (Tm_xPr_1 – x)₂Fe_16.5Cr_0.5 compounds crystallize with the formation of the rhombohedral Th₂Zn₁₇-type structure for the compositions with x = 0–0.4 and the hexagonal Th₂Ni₁₇-type structure for the compositions with x = 0.8–1 and x = 0.75–1, respectively. Both structures coexist in the (Tm_xPr_1 – x)₂Fe₁₇ and (Tm_xPr_1 – x)₂Fe_16.5Cr_0.5 compounds with x = 0.5–0.75 and x = 0.5–0.6, respectively. The (Tm_xPr_1 – x)₂Fe₁₇ 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 –ΔS_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.