The influence of the Mn substitution by Fe atoms on the magnetocaloric and magnetic properties of the martensitic Ni50Mn36Sn14 Heusler-type compound has been investigated using magnetization measurements. The insertion of Fe atoms reduces the Mn-Mn AF interactions resulting in (i) a systematic decrease in the martensitic transition temperature, down to its disappearance at 15 at. % of Fe, (ii) an enhancement of the saturation magnetization, and (iii) a monotonic increase in the L21-type phase Curie temperature. The Fe substitution also induces metamagnetic transition from an incipient AF to a noncollinear spin configuration for applied magnetic fields higher than 3 T in the case of 3 and 7 at. % Fe substitutional. The exchange-bias effect is only found in compounds with a well-defined martensitic phase transition (Fe content lower than 10 at. %). The maximum of the inverse magnetic entropy change, for a field variation of 5 T, is about +12 J kg−1 K−1 and it is nearly constant for Fe content up to 7 at. %. This observation suggests that the Ni50(Mn1−xFex)36Sn14 Heusler-type compounds could be used to prepare composites with potential for technological application in magnetic refrigerators.
Various compositions of the system BaxSr1−xTiO3 (BST) have been elaborated both as fine powders and ceramic monoliths, using the co-precipitation route within a warmed supersaturated solution of oxalic acid. The appropriate stoichiometry was determined from the mixtures of precisely titrated aqueous solutions of cations chlorides (SrCl2, BaCl2, and TiCl4). The reason of this process was to apply low sintering temperature in production of BST samples with ultra-fine powders. These powders primarily calcined at (850˚C) for (5 hr) were used to elaborate ceramics after pellets sintering at (1200˚C) during (8 hrs). Indeed, XRD patterns were confirmed that the samples are a pure phase and a perovskite cubic structural type at (x = 0, 0.5, 0.6). Whereas, (x = 0.7, 0.8, 0.9, 1) showed a tetragonal phase. There is agreement between the FTIR and XRD analysis, by the relation of the wave vector (K) and lattice constant. It was deduced a stimulated relation between (x) and (K). The results of TEM, they were clear that the lowest particle sizes investigated of BST powders nearly (36 -50 nm).
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