Sensors and Actuators B 126 (2007) 318–323 Development of thin microwires with low Curie temperature for temperature sensors applications V. Zhukova a , J.M. Blanco a , M. Ipatov b , A. Zhukov b,c,∗ , C. Garc´ ıa b , J. Gonzalez b , R. Varga b , A. Torcunov d a Dpto. F´ ısica Aplicada I, EUPSD, UPV/EHU, Plaza Europa 1, San Sebasti´ an 20018, Spain b Dpto. F´ ısica de Materiales, Fac. Quimicas, Universidad del Pais Vasco, 20009 San Sebastian, Spain c Magnetic and Cryoelectronic Systems Ltd., Bozhenko str., 4/1, Moscow 121351, Russia d TAMAG Ib´ erica S.L., Parque Tecnol´ ogico de Miram´ on, Paseo Mikeletegi 56, 1 ◦ , 20009 San Sebasti ´ an, Spain and AmoTecLtd, Titulescu str. 47 ap.3, MD2032 Kishinev, Moldova Available online 16 February 2007 Abstract A novel family of magnetic materials, thin ferromagnetic metallic glass-coated wires (1/30 m in diameter) produced by the Taylor–Ulitovsky method present excellent magnetic properties such as magnetic bistability, GMI effect or enhanced magnetic softness attracting great attention for sensor applications. In this paper we report novel results on the fabrication and magnetic characterization of a number of Co–Fe–Ni–Si–B and Co–Fe–Cr–Si–B microwires with total diameter between 15 and 37 m fabricated by the Taylor–Ulitovsky method with low Curie temperature possessing also good magnetic softness and high GMI effect. Magnetization, hysteresis loops, magnetic susceptibility and their magnetic field dependence and GMI effect at frequencies up to 500 MHz have been measured. Few samples possessing low T C (below 100 ◦ C) also present high GMI effect with GMI ratio achieving 110% at 100MHz. Additions of Ni or Cr to the conventional Co–Fe–Si–B composition with vanishing magnetostriction constant resulted in significant decreasing of the Curie temperature. Concrete applications have been designed such as the temperature sensors applications based on drastic change of the magnetic properties in the vicinity of Curie temperature. © 2007 Elsevier B.V. All rights reserved. Keywords: Amorphous microwire; GMI effect; Magnetic anisotropy; Curie temperature 1. Introduction A novel family of thin ferromagnetic metallic microwires (1/30 m in diameter) coated by glass with unusual magnetic, such as magnetic bistability, GMI effect and good magnetic soft- ness attracts recently considerable attention [1–3]. Recently a significant progress on tailoring of magnetic properties of glass- coated microwires allows to enhance significantly their magnetic softness and the GMI ratio (up to about 600%) after special thermal treatment or by proper composition selection [1,2]. One of the possible applications of such thin microwires is based on the ferromagnetic–paramagnetic transition at Curie temperature, when the magnetization and magnetic permeability drops down. Usually the Curie temperature of Fe and Co-rich ∗ Corresponding author. Tel.: +34 943 018611; fax: +34 943 017130. E-mail address: wupzhuka@sc.ehu.es (A. Zhukov). amorphous microwires is about 300–400 ◦ C [4]. On the other hand it is known that the addition of Cr and Ni results in drastic decrease of the Curie temperature. In this way a wide variety of microwires with the Curie temperatures ranging between room temperature and 400 ◦ C can be obtained. This can give the possibility to use the ferromagnetic–paramagnetic transi- tion at around Curie temperature to detect the temperature. Such changes can be detected through the change of the magnetiza- tion, magnetic permeability or even GMI effect closely related with the ferromagnetic origin of magnetic conductor. The GMI effect was initially interpreted in terms of the clas- sical skin effect in a magnetic conductor as a consequence of the change in the penetration depth of the ac electric current caused by a dc applied magnetic field, as described elsewhere [5]. The dc applied magnetic field introduces significant changes in the circular permeability, μ  . Therefore, the penetration depth also changes through and finally results in a change of impedance, Z [5]. This “scalar” model has been significantly modified after- 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.02.019