Non-Monotonic Variation of Magnetocaloric Effect in the Tm_2(Fe,Mn)_17 and Tm_2Fe_(16)-Tm_2Fe_(19) Systems

摘要

The magnetocaloric effect (MCE) of the Tm_2Fe_(l7-x)Mn_x (x= 0, 0.2, 0.5, 1, 1.5) and Tm_2Fe_(16), Tm_2Fe_(17), Tm_2Fe_(18), Tm_2Fe_(19) compounds has been investigated by means of magnetic measurements. The MCE exhibits two peaks near the temperatures of ferromagnetic ordering Θ_T and T_N for Tm_2Fe_(17), Tm_2Fe_(18), Tm_2Fe_(19) compositions or one peak near T_c for the Tm_2Fe_(16) and Tm_2Fe_(17-x)Mn_x (x≥ 0.2) ferromagnets. The peak entropy change -ΔS_M varies non-monotonically in the systems, with the maximal values -3.25 J/kg K at T=310 for Tm_2Fe_(16.8)Mn_(0.2) and -3.5 J/kg K at T= 290 K for Tm_2Fe_(17) in a field of 5 T. On the contrary, the relative cooling power decreases monotonically with decrease of Fe content because of contraction of the -ΔS_M peaks.