ИСТИНА

The quasiternary intermetallic family Gd3Ni6XY {X, Y = Si, Al and Ga} presents interesting magnetic and magnetocaloric properties, given by the complex magnetic structure arising from the combination of the rare earth, transition metal and p-block elements {Si, Al and Ga}. Particularly, the existence of two consecutive magnetic phase transitions occurring at different temperatures makes these materials to display a considerable magnetocaloric effect in a wide temperature range. This fact, together with the ability to exchange heat rapidly, makes these alloys good candidates for magnetic refrigeration applications.In the present work, three compounds of the Gd3Ni6XY family have been produced and investigated: Gd3Ni6AlGa, Gd3Ni6SiAl and Gd3Ni6SiGa. All the compounds present a cubic unit cell with Ce3Ni6Ga2-type structure (space group Im-3m, N 229, cI44). In all of them, a paramagnetic to ferromagnetic phase transition takes place (TC), followed by a spin reorientation transition at lower temperatures (TM). The Curie temperature decreases significantly in the alloys containing Si, compared to the one without it. This shift can be explained in terms of the monotonic decrease of the Curie temperature with the atomic radius observed in [1], as the Si is the smallest p-block element present in this work. Therefore, this dependence could be used to tune the critical temperature as demanded by the refrigeration cycle. Each magnetic transition produces a peak in the magnetic entropy change, giving a direct magnetocaloric effect. The overlapping of both peaks gives rise to a table-like region keeping a high value of the magnetic entropy change in a wide temperature range, which is desirable to design a magnetic refrigerator. Although the maximum value of the magnetic entropy change is not too high compared to a first-order transition, 4.71 J/kg for dH = 5 T in the case of Gd3Ni6AlGa, the table-like behavior generates an important refrigerant capacity of 483 J/kg. The operating temperature interval for this sample could be suited for nitrogen liquefaction, for instance.