The effect of mechanical stress on Ni 63.8 Mn 11.1 Ga 25.1 microwire crystalline structure and properties A.S. Aronin a , G.E. Abrosimova a , A.P. Kiselev a , V. Zhukova b , R. Varga c , A. Zhukov b, d, * a Institute of Solid State Physics RAS, Chernogolovka, Russia b Dpto. Fisica de Materiales, Fac. Quimicas, UPV/EHU, 20009 San Sebastian, Spain c Inst. Phys., Fac. Sci., UPJS, Park Angelinum 9, Kosice, Slovakia d IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain article info Article history: Received 10 May 2013 Received in revised form 9 July 2013 Accepted 11 July 2013 Available online 3 August 2013 Keywords: A. Composites A. Magnetic intermetallics B. Crystallography B. Magnetic properties B. Martensitic transformations B. Shape-memory effects abstract We studied structure and magnetic properties of Heusler alloy microwires. The dependence of the phase composition of the annealed microwires on the presence of glass coating has been found. The crystalline structure of the glass-coated samples is composed of two cubic crystalline phases of different density. The samples annealed without coating are in the single-phase state. The two-phase state is supposed to be caused by intrinsic stresses resulted from the action of opposite sign stresses in different microwire sections. The magnetic properties of the fabricated Heusler-type microwires differ from their bulk and thin film counterparts. Annealing of microwires considerably affect magnetic properties at room tem- perature. Unusual magnetic behavior is connected with two-phase structure of microwires. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Considerable recent attention has been focused on studies and applications of glass-coated microwires prepared by the Tailor-Ulitovsky [1] method that enables fabrication of microwires 1e60 mm in diameter coated by glass (thickness of coating 0.5e 20 mm). At present it is possible to obtain ferromagnetic and non- magnetic microwires with amorphous, crystalline, nanocrystalline or granular structures. Amorphous and nanocrystalline soft mag- netic microwires present considerable interest for various industrial sectors owing to a number of unusual magnetic and transport properties, such as the giant magnetoimpedance (GMI) effect, the giant magnetoresistance (GMR) effect, magnetic bistability and natural ferromagnetic resonance [2e8]. It must be pointed out, that recently, certain progress in improvement of soft magnetic proper- ties and achievement of a high GMI effect of glass-coated microwires has been reported at the laboratory level [2e4]. This gives rise to development of industrial applications for low magnetic field detection in various industrial sectors [2,3]. From the point of view of technical applications, the GMI effect, consisting in large sensitivity of the impedance of magnetically soft conductor to applied magnetic field, is most attractive for application in magnetic sensors. The GMI effect has been successfully explained in terms of classical electro- dynamics through the influence of magnetic field on penetration depth of electrical current flowing through the magnetically soft conductor [2e4]. The main interest in the GMI effect is basically due to excellent magnetic field sensitivity suitable for low magnetic field detection. The cylindrical shape and high circumferential perme- ability observed in amorphous wires are quite favorable for achievement of a pronounced GMI effect usually observed in amorphous materials with nearly-zero magnetostriction constant [2e4,9]. The preparation of glass-coated microwires involving simulta- neous solidification of composite microwire consisting of a ferro- magnetic metallic nucleus inside the glass coating introduces considerable residual stresses inside the ferromagnetic metallic nucleus [2,4,6,8]. The strength of internal stresses is determined by the thickness of the glass coating and metallic nucleus diameter. This additional magnetoelastic anisotropy affects soft magnetic properties of glass-coated microwires. Therefore, the microwire * Corresponding author. Dpto. Fisica de Materiales, Fac. Quimicas, UPV/EHU, 20009 San Sebastian, Spain. Tel.: þ34 943018611; fax: þ34 943017130. E-mail addresses: arkadi.joukov@ehu.es, arcadyzh@mail.ru (A. Zhukov). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.intermet.2013.07.010 Intermetallics 43 (2013) 60e64