Influence of iron substitution on structural, magnetic, and magnetocaloric properties of Tb$_2$Fe$_1$$_7$$_-$$_x$Al$_x$ compounds synthesized by arc melting
Résumé
In the present work, the structure and magnetic and magnetocaloric properties of the Tb$_2$Fe$_1$$_7$$_-$$_x$Al$_x$ compounds with x = 0, 0.25, 0.5, 0.75, and 1 were studied. These compounds were synthesized by arc furnace without subsequent annealing. Their crystal structure is a Th$_2$Ni$_1$$_7$ hexagonal structure with a P6$_3$/mmc space group. The Rietveld refinement of the X-ray diffractograms allowed for determining the structural parameter variations with different amounts of aluminum. Lattice parameters and the unit cell volume increase with aluminum amounts while the c/a ratio remains nearly constant. The Tb$_2$Fe$_1$$_7$$_-$$_x$Al$_x$ compounds exhibit a second-order magnetic phase transition from a ferromagnetic state to a paramagnetic state. The Curie temperature (TC) increases with the aluminum content, the observed effect is due to the magnetovolumic effect. The saturation magnetization (MS) decreases with the increase of Al content. Magnetic entropy and relative cooling power (RCP) decrease as the aluminum content increases. Tb$_2$Fe$_1$$_7$$_-$$_x$Al$_x$ compounds have a moderate magnetocaloric effect and a tunable operating temperature interval.
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