Journal of Magnetism and Magnetic Materials 102 (1991) 63-66 North-Holland Thermal dependence of the anisotropic contribution to the stress derivative of the magnetostriction in ( Co,.,Fea,S),,Si,,B,, amorphous alloy J. Gonzglez, J.M. Blanco, P.G. Barbon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH Departamento de Fisica de Materiales, Facultad de Ciencias Quimicas, Universidad de1 Pa& Vasco, 20009 San Sebastian, Spain and K. Kulakowski Institute of Physics and Nuclear Techniques, Academy of Mining and Metallurgy, 30059 Cracow, Poland Received 13 May 1991; in revised form 19 June 1991 The anisotropic part A’” of the material constant A = ah /aa, where h is the magnetostriction and (T is an applied tensile stress, is separated as the difference of the results on A for perpendicular and longitudinal field annealing. We find that Aa” has a maximum which is dependent on the temperature of measurement. The two-ion character of this maximum is confirmed by some model arguments, which are valid at low temperatures. 1. Introduction Recently the (Co,,,Fe,,,),,Si,,B,, amor- phous system has been investigated carefully [1,2] because of its unusual behaviour while annealing in the presence of tensile stress and magnetic field parallel to the stress. There, some metastable states were found to be possible [3] in as-quenched samples, which could not be obtained within any model of equilibrium states. On the other hand, the crystallization temperature of the system is particularly low (400 o C>, which allows one to believe that the field-induced directional ordering of atom pairs reaches its equilibrium value. Usually it is difficult to separate the one-ion and two-ion contributions to various magnetic quantities, such as magnetostriction and magnetic anisotropy. The comparison of experimental data with the Callens’ model [4] is of common use, for insulators and metals as well. Recently some model calculations were developed [5] on the influence of anisotropic hopping of electrons, which was an itinerant effect on the magnetoelas- tic constants and magnetic anisotropy. The aim of this article is to separate the two-ion anisotropic effect both from experiment and theory, and to try to compare them. 2. Experiment Amorphous alloy ribbons of nominal composi- tion (Co,,Fe,,)BoSi,oB,, were annealed under the action of the magnetic field parallel or per- pendicular to the ribbon axis, as described in refs. [2,6]. The annealing temperature was 340 o C, and the annealing time was 40 h. The equilibrium states were therefore obtained in the presence of an effective magnetic field (the Curie tempera- ture for this sample is 440 o 0. The values of the external field were 4000 A/m for parallel field and 360 l&/m for perpendicular one. 0304~8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. All rights reserved