Journal of Magnetism and Magnetic Materials 310 (2007) 48–50 Magnetic and transport properties of Cu 2 MnAl Heusler alloy prepared by rapidly quenched method Do Bang, Nguyen Huy Dan à , Nguyen Anh Tuan, Nguyen Xuan Phuc Institute of Materials Science, VAST, 18 Hoang Quoc Viet, Hanoi, Vietnam Received 4 November 2005; received in revised form 30 March 2006 Available online 23 August 2006 Abstract The Cu 2 MnAl alloy was prepared by rapidly quenched (suction-casting and melt-spinning) methods with various thicknesses of 20, 40 and 1000 mm. The X-ray diffraction (XRD) patterns of the fabricated samples show a single phase of Cu 2 MnAl. All the samples reveal soft magnetic behavior with coercivity below 1.6 kA/m and Curie temperature of about 600 K. Resistance of the alloy behaves as a linear function of applied magnetic field. Magnetoresistance (MR) ratio depends on the thickness of the samples and achieves 0.8% at the field of 240 kA/m for the sample with thickness of 20 mm. The variation of the properties of the alloy can be interpreted by the difference of energy band structure caused by defects in the alloy. r 2006 Elsevier B.V. All rights reserved. Keywords: Magnetoresistance; Heusler alloys; Rapidly quenched method; Spintronic materials 1. Introduction Recently, researches on high spin-polarization magnetic materials, which are known as spin-polarized electron sources in various spintronic devices, have been attracting much attention [1,2]. However, these materials commonly require a low temperature and high magnetic field environment to get high spin-polarization. To fulfill these two problems the half-metallic alloys are chosen in many projects [3–9]. The Heusler alloys with stoichiometric composition of X 2 YZ (where X and Y are transition metals and Z is a III, IV or V group element) and high Curie temperatures are able to integrate into semiconduc- tors because their lattice parameters and energy gap are compatible [3,4]. In the ideal case, they are predicted to have 100% spin polarization at the Fermi level (E F ) due to a metallic density of states in one spin direction (usually spin-up) combined with a band gap in the other spin direction (spin-down) [5]. Therefore, there are many efforts to research and produce Heusler alloys, which have been used as electrodes in tunneling junctions or spin-injection sources [6,7]. In this work, we investigate magnetic and transport properties of Cu 2 MnAl Heusler alloy prepared by rapidly quenched method with various quenching rates. 2. Experiment High purity elements of Cu, Mn and Al were used as starting materials to prepare pre-alloy of Cu 2 MnAl by arc melting method. The pre-alloy was then used to fabricate rod and ribbon samples by suction-casting and melt- spinning methods, respectively. The suction-casting and melt-spinning processes were performed in Ar atmosphere on arc-furnace and single role melt-spinning apparatus. The variation of sample thickness is equivalent to variation of quenching rate of the alloy, the smaller the thickness the higher the quenching rate of alloy is. The cast rod has a thickness of 1000 mm and the ribbons have thicknesses of 40 and 20 mm which were made at Cu-wheel tangential velocities of 20 and 40 m/s, respectively. A portion of the samples was powdered and used for X-ray diffraction (XRD) measurement on SIEMENS D-5000 equipment. The field and temperature dependences of the magnetization of the samples were measured on vibrating sample magnetometer (VSM). The thermal-resistance and ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.07.027 à Corresponding author. Tel.: +84 4 7567155; fax: +84 4 8364403. E-mail address: dannh@ims.vast.ac.vn (N. Huy Dan).