ИСТИНА

Ho6MnBi2, Ho6FeBi2, Ho6(Mn0.5Fe0.5)Bi2, and Ho6(Mn0.75Fe0.25)Bi2 (which crystalize in the Fe2Ptype structure) have been studied using magnetic techniques in order to explore the suitability of the intermetallic family Ho6(Fe,Mn)Bi2 as a magnetocaloric material. Besides, the critical behavior of the paramagnetic (PM) to ferromagnetic (FM) transitions has also been investigated to obtain a deeper understanding of the range of the magnetic interactions. The obtained critical exponents β, γ and δ point to long-range order interactions, as they are close to those of the Mean Field Universality class. The magnetocaloric effect in the four compounds shares common properties: it spans over a very broad temperature range, limited by the PM-FM transition at high temperature and a spin-reorientation one at low (see Fig. 1), with more than 200 K for Ho6MnBi2 at 5T and, on the other limit, 80 K for Ho6FeBi2. They present very high values of the refrigerant capacities (from 520 J/kg to 709 J/kg at 5T) and good magnetic entropy changes (from 3.4 to 5.7 J/(kgK) at 5T), as well as a flat and wide temperature span for the working temperature range. The change in properties with composition proves that the magnetocaloric properties can be tuned in this intermetallic family to accommodate different refrigeration applications. The magnetocaloric scaling laws have been successfully tested and universal curves for the magnetic entropy change have also been obtained in the PM-FM transition region.