J. Phys.: Condens. Matter 9 (1997) 5671–5685. Printed in the UK PII: S0953-8984(97)81257-X Magnetic and transport properties of Fe–Zr–B–(Cu) amorphous alloys J M Barandiar´ an†, P Gorria†‖, I Or´ ue†‖, M L Fern´ andez-Gubieda†, F Plazaola†, J C G´ omez Sal‡, L Fern´ andez Barqu´ ın‡ and L Fournes§ † Departamento Electricidad y Electr´ onica, Universidad del Pais Vasco, PO Box 644, E-48080 Bilbao, Spain ‡ F´ ısica de la Materia Condensada, Universidad de Cantabria, E-39005 Santander, Spain § Laboratoire de Chimie du Solide, Universit´ e Bordeaux I, France Received 24 January 1997 Abstract. FeZrB metallic glasses present magnetic properties that are enhanced compared to the pure FeZr ones. In particular, a large increase of the Curie temperature has been found. Magnetic and M¨ ossbauer measurements show a decrease of the spin-glass character and a parallel homogenization of the hyperfine-field distribution as the boron concentration increases. Resistivity versus temperature measurements show a change in behaviour with B content: in the samples with small amounts of boron, a minimum in the resistivity versus temperature curves appears near the Curie temperature, while samples with high boron content show a low-temperature minimum, characteristic of most metallic glasses. The analysis of the results suggests that the evolution of the magnetic behaviour is related to changes in the density of states at the Fermi level, rather than to changes in the Fe–Fe distances. This is in agreement with published data on the specific heat of FeZr and FeB glasses. The influence of boron is shown to greatly enhance the weak itinerant ferromagnetism of FeZr glasses, leading to stronger ferromagnetic behaviour. The characteristic features of the resistivity are analysed in terms of localization effects on the conduction electrons, which extend to higher temperatures in the low-boron-content alloys. 1. Introduction Fe-rich FeZr glasses have attracted much interest in the past few years [1–5]. They are among the most peculiar of the magnetic systems, displaying re-entrant spin-glass (RSG) behaviour and Invar characteristics. An initial theoretical explanation was based on the existence of magnetic inhomogeneities caused by variations of the Fe interatomic distances. This would lead to a non-collinear state with a net ferromagnetic component, developing a transverse spin freezing (TSF) when entering into the RSG state [6]. An alternative view has been proposed, which considers the existence of ‘spin clusters’ created by density variations during the casting of the ribbons [7]. In addition, it has been suggested that, even in these Fe-rich alloys, the observed magnetic phenomena are reminiscent of a superparamagnetic behaviour, with particular relaxation effects [8–10]. From an experimental point of view some facts are clearly established: the Curie temperature T C increases with Zr content (up to about 25 at.% Zr, for which T C ≈ 268 K [11]), but the spin-glass temperature (T RSG ) decreases, vanishing at about 11 at.% Zr. On the other hand, the Curie temperature shows ‖ Present address: Departamento de F´ ısica, Universidad de Oviedo, Avenida Calvo Sotelo, s/n, E-33007 Oviedo, Spain. 0953-8984/97/265671+15$19.50 c  1997 IOP Publishing Ltd 5671