Papers by Author: L. Escoda

Abstract: We report the effect of shorttime vacuum annealing, during 10 minutes at 923 K, 973 K, 1023 K and 1073 K, on magnetostructural properties of as-quenched ribbons of Ni_45.5Mn₄₃In_11.5 Heusler alloy. The martensitic transformation is strongly sensitive to annealing treatments. The martensitic phase starting temperature is significantly shifted from 239 K towards higher temperatures around 370 K. It suffers a break down in two peaks when a field equal or higher than 500 Oe is applied to the as-quenched sample. This effect is not detected in the transformation of annealed ribbons but its signature can be observed at low temperature. Moreover, under high magnetic field up to 30 kOe temperatures associated with both martensitic and reverse transitions do not change for annealed samples, meanwhile the magnetization difference between austenite and martensite increases with the field. Nevertheless, it almost remains unchanged in the as-quenched ribbon.

Abstract: Glass-coated Cu-Mn-Ga microwires were fabricated by Taylor-Ulitovsky technique. By means of energy dispersive spectroscopy microanalysis, an average alloy composition of Cu56Ga28Mn16 was determined. The temperature dependence of magnetization measured at a low magnetic field showed the coexistence of two ferromagnetic phases. The Curie temperature of one phase is 125 K and above room temperature for the other one. X-ray diffraction at room temperature and at 100 K reflects the presence of the same three crystalline phases corresponding to the cubic B2 Cu-Mn-Ga structure as a main phase and the minor phases of fcc Cu rich solid solution with Mn and Ga and the monoclinic CuO.