Synthesis by rapid solidification and sparkplasma sintering of single-phase DyNi5

Abstract

Theoretical and experimental studies show that the binary compounds RNi5,with R = Tb, Dy, Ho, and Er, are attractive magnetic materials for magnetic refrigerationin the temperature range of H2 liquefaction. For such a purpose, highsaturation magnetization values and moderate-to-low values of specific heat aretwo of their favorable characteristics. Furthermore, their anisotropicmagnetization behavior could produce a high-rotating magnetocaloric effect. Inthis work, we report the synthesis and characterization of partially textured melt-spunribbons obtained by ultrafast solidification using the melt-spinning techniqueand their consolidation into high-density sintered bodies by applying the sparkplasma sintering (SPS) technique. Particular attention was paid to replicating the partial anisotropic magnetization properties of the melt-spun ribbons in the sintered sample. The melt-spun ribbons were synthesized at a linear copperwheel speed of 20 ms-1 from a solid ingot obtained by arc melting(both processes were carried out under a high-purity Ar atmosphere). The densificationprocess was performed in about 6.7 minutes. The elemental chemical compositionand hexagonal crystal structure of the CaCu5 type of DyNi5determined by EDS analysis and X-ray diffraction were reproduced in thesintered sample, which had a relative density of 95.5%. The magnetizationmeasurements also show that the magnetic and anisotropic properties of theribbons were reproduced in the sintered sample. The Curie temperature (TC)of the DyNi5 phase was ~ 11.8 K, while at 2 K and 5 T the saturationmagnetization MS between the pressing direction (MS= 100 Am2kg-1) and the perpendicular plane (MS= 67 Am2kg-1) showed a difference of 23 Am2kg-1.For a magnetic field variation of 2 and 5 T, the maximum values of magneticentropy change |ΔSM|maxalong the pressing direction were 10 and 16 Jkg-1K-1,respectively. Furthermore, a rotational magnetic entropy change |maxof 3.2 Jkg-1K-1 was determined between the pressing and perpendiculardirections.