Journal of Magnetism and Magnetic Materials 249 (2002) 108–112 DSC studies of finemet-type glass-coated microwires V. Zhukova a , S. Kaloshkin b, *, A. Zhukov c,d , J. Gonzalez a a Dpto. F! ısica de Materiales, Fac. Qu ! ımicas, UPV/EHU, 1072, 20080, San Sebasti ! an, Spain b Department of Physical Chemistry, Moscow Steel and Alloys Institute, Leninsky Avenue, 4, 117936 Moscow, Russia c Donostia International Physics Centre, P.M. De Lardizabal, 4, 20018, San Sebasti ! an, Spain d ‘‘TAMag’’ S.L: c/Jose Abascal 53, Madrid, Spain Abstract Effect of cyclic annealing on the Curie temperature, T C ; of Fe 71.8 Cu 1 Nb 3.1 Si 15 B 9.1 glass-coated microwires has been investigated. T C of the initially amorphous alloy strongly depends on annealing conditions. Monotonic increase of T C from 579 up to 591 K related with the relaxation of amorphous structure was found during annealing at 633 K. After a certain annealing time in the temperature range 713–813 K, T C splits into two Curie temperatures with values higher (T C1 ) and lower (T C2 ) than that of the initial state. Further increase of the annealing time, t ann ; tends to increase T C1 and decrease T C2 : Such peculiar behavior is related with the decomposition of the amorphous matrix and the beginning of the devitrification process. r 2002 Elsevier Science B.V. All rights reserved. Keywords: DSC; Glass-coated microwires; Curie temperature; Structural relaxation 1. Introduction Glass-coated amorphous microwires have at- tracted much attention of the researchers the last few years as one of the most interesting magnetic materials for different kinds of sensor applications [1,2]. But rather extensive experimental data on magnetic properties are supported with an infor- mation about stability, structural, kinetic and other physical properties on these materials. On the other hand, Fe-based nanocrystalline materials (most typical of the composition Fe 73.5 - Cu 1 Nb 3 Si 13.5 B 9 with trademark finemet) are widely studied mainly because of their excellent magnetic softness related with the nature of their micro- structure which consists basically of small crystal- lites (mean grain size of 10 nm) embedded in an amorphous residual matrix [3–5]. These materials are obtained by devitrification of the precursor amorphous alloy in the range of 500–6001Cfor1h (i.e., at temperatures between the first and second crystallization peaks). The Curie temperature T C of the amorphous ferromagnetic alloys is defined by both the average chemical composition and the particularities of the structural state. Since the value of T C is a very sensitive parameter to structural relaxation of amorphous alloys, it is often used for studying this process. It is convenient to study the dynamics of T C change by the DSC method. There is a peak of heat capacity on the calorimetric curves at heating *Corresponding author. Tel.: +7-095-230-4667; fax: +7-95- 247-6001. E-mail address: ksd@phch.misa.ac.ru (S. Kaloshkin). 0304-8853/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0304-8853(02)00515-2