L Journal of Alloys and Compounds 323–324 (2001) 422–426 www.elsevier.com / locate / jallcom Composition and annealing dependence of magnetic properties in amorphous Tb–Co based alloys * M.L. Soltani , N. Chakri, M. Lahoubi ´ ´ Laboratoire de Magnetisme, Dpt. de Physique, Universite d’ Annaba, BP 12, Route d’ El-Hadjar, 23000 Annaba, Algeria Abstract The aim of the work is to study the magnetic properties of Tb Co amorphous alloys with respect to the composition and annealing 12x x temperature. The samples have been prepared by the dc triode co-sputtering. The most important results are: (1) Curie temperature is higher than the room temperature for the magnetic samples with Co content x.0.6, before annealing rises T with Co content. c Crystallization commences at approximately 4008C. (2) A significant high field susceptibility, even up to 8 Tesla, confirms the sperimagnetic structure. (3) A biaxial anisotropy occurs before annealing due to stress, but a uniaxial anisotropy is induced by the field annealing; the anisotropy value is dependent upon composition.  2001 Elsevier Science B.V. All rights reserved. Keywords: Magnetic films; Amorphous materials; Anisotropy; Magnetization; Amorphization 1. Introduction first approximation [8,9], the mean magnetic moments do not depend upon the surrounding atomic arrangement, but The magnetic structure of the rare earth–transition metal depends upon the chemical composition in either crys- amorphous alloys have been intensively studied [1–5]. tallized or amorphous state. As an example, critical content Among all researched properties, the magnetization and for magnetic disappearance in amorphous is greater than in the shape of hysteresis loops are dependent upon the alloy crystallized. composition, heat and mechanical treatment. Amorphous The aim of the present work is to describe the magnetic alloy films are usually prepared by sputtering different properties in the Tb Co amorphous alloys with various 12x x procedures. compositions for an as-cast and after magnetic field The random anisotropy model of Harris, Plichke and annealing. Changes of the composition and of annealing Zukermann [6] describes the competition between ex- temperature will be considered in the influence upon the change interactions and random anisotropy in amorphous magnetization process, the magnetic anisotropy and alloys. The model accounts for the sperimagnetism, i.e. the sperimagnetism. Tb Co amorphous thin films are 12x x non-colinear arrangement of rare-earth magnetic moments chosen as the system because of its relatively high Curie in 3d –4f alloys due to the large random anisotropy of temperature and its good resistance against oxidation. rare-earth atoms ( R). Consequently, the magnetization should be free from anisotropy at large scale and feature high anisotropy at short scale. These amorphous alloys are 2. Experimental characterized by large magnetic domains, so-called Imry and Ma domains, which also occurs in the case of strong 2.1. Preparation of amorphous films exchange interaction J and weakly random anisotropy D [7]. Rare earth –transition metal amorphous films Tb Co 12x x In the case of magnetism, the amorphous state changes ( x50.6–0.8) samples were prepared by dc triode co-sput- the magnetic properties due to the narrow relation between tering from various targets onto silica substrates with crystallographic and magnetic structure. However, in the thicknesses of about 1 mm. The thickness range is from ˚ 2000 to 5000 A. The samples were characterized in crystallographic structure by X-ray diffraction and by *Corresponding author. Fax: 1213-8-87-1712. E-mail address: ml soltani@yahoo.com (M.L. Soltani). Rutherford Back Scattering (RBS) in compositional and ] 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01102-1