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1200-G09-03

Thermal Annealing Influence on Magnetic and Structural Properties of Cu56Ga28Mn16 Microwires V. M. Prida1, V. Vega1, J. L. Sánchez-Llamazares1, M. L. Sánchez1, J.D. Santos1, B. Hernando1, Ll. Escoda2, J. J. Suñol2, C. García3 and C. A. Ross3 1 Depto. Física, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo, Asturias, Spain, 2 Universidad de Girona, Campus Montilivi, Lluís Santaló s/n, 17003, Cataluña, Spain, 3 Dept. Material Science & Engineering, MIT, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, U.S.A. ABSTRACT We report on the crystalline structure, morphology and thermomagnetic properties of glass-coated magnetic microwires with Cu56Ga28Mn16 composition, as well as the thermal annealing influence on its magneto-structural properties. As-cast CuMnGa microwires exhibit a majority cubic B2 phase, and upon annealing at temperatures up to 573 K a new hexagonal phase appears coexisting with the cubic B2 major phase. Thermal annealing treatments also shift the Curie temperature about 150 K with respect to the one for the as-cast microwire. Furthermore, the signature of a structural phase transition is observed for the microwire annealed at 523 K. INTRODUCTION Ferromagnetic glass-coated microwires are of considerable interest as multifunctional magnetic materials. They display attractive features due to the recent tendency on miniaturization of the modern sensors and devices stimulating the development of functional materials with reduced dimensionality and with improved effects, as shape memory [1] and magnetocaloric ones [2]. Both, microwire shape and glass-coating mechanical reinforcement are suitable features for applications in magneto-mechanical sensors and actuators and may significantly influence the microwire magnetic behavior [3]. Recently, attention has been drawn to investigate mechanical, magnetic and magnetostructural properties in bulk polycrystalline Cu-Ga-Mn alloys due to its high ductility, martensitic phase transformation and potential application as ferromagnetic shape memory alloy [4-7]. In the present study, we report on the crystalline structure, morphology and magnetic properties of glass-coated magnetic microwires with Cu56Ga28Mn16 sample composition, as well as the thermal annealing influence on its magneto-structural properties, with the aim of finding a new ferromagnetic shape memory and magnetocaloric material candidate. EXPERIMENTAL Cu-Ga-Mn glass coated microwires having an inner metallic nucleus diameter around 17 µm and glass-coating outer shell diameter about 26 µm, were produced by the Taylor-Ulitovsky method [8, 9]. Starting alloys of nominal composition Cu50Ga25Mn25 were prepared by arcmelting the pure elements (>99.9%) in Ar atmosphere. Subsequently, when the metallic alloy and the Pyrex glass coating were simultaneously molten the so-formed microwire was drawn and rolled onto a rotating coil and quenched to room temperature. The samples thus obtained were in

the form of a tiny metallic wire with the dimensions above mentioned. Thermal annealing treatmen