IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 41 (2008) 095005 (7pp) doi:10.1088/0022-3727/41/9/095005 Annealing effects on the magnetization reversal and domain wall dynamics in bistable amorphous glass-covered microwires R L Novak 1,3 , J P Sinnecker 1 and H Chiriac 2 1 Instituto de F´ ısica, Universidade Federal do Rio de Janeiro, CP 68528, 21941-972 Rio de Janeiro, Brasil 2 National Institute of Research and Development for Technical Physics, 47, Mangeron Blvd., Ias ¸i 700050, Romania E-mail: novak@fi.infn.it, jps@if.ufrj.br and hchiriac@phys-iasi.ro Received 30 November 2007, in final form 19 February 2008 Published 7 April 2008 Online at stacks.iop.org/JPhysD/41/095005 Abstract We study the mechanism of domain wall depinning and propagation in Fe 77.5 Si 7.5 B 15 amorphous glass-covered microwires. These samples are ferromagnetic and spontaneously present the striking property of magnetic bistability, with the magnetization reversal process characterized by a single giant Barkhausen jump. This process allows one to easily measure the velocity of a domain wall propagating along the sample as a function of applied magnetic field and temperature and thus determine the wall mobility and the influence of different damping mechanisms on the domain wall dynamics. A discussion on the effects of thermal treatment on the wall mobility is presented. Domain wall velocities of the order of 850 m s −1 are measured. The temperature dependence of the wall mobilities established at 300 and 77 K, for as-cast and annealed samples, clearly shows a damping mechanism arising from the structural relaxation mechanism and from domain wall/atomic defect interactions, the second one playing a major role in the dissipative dynamics of magnetization reversal through depinning and domain wall propagation in Fe 77.5 Si 7.5 B 15 microwires. 1. Introduction The study of magnetic reversal processes in ferromagnetic materials is an old and important subject, especially nowadays with the increasing need for fast magnetic sensors and applications, such as magnetic logic devices [1–6]. Amorphous glass-covered Fe 77.5 Si 7.5 B 15 ferromagnetic microwires prepared by the Taylor–Ulitovsky technique are materials that allow the magnetization switching process to be studied in thin single domain cylindrically shaped samples. Due to the specific characteristics of this material, the magnetization switching process occurs through the depinning and propagation of a single domain wall, which is an optimum scenario to study domain wall properties and its propagation dynamics [7–12]. These microwires have further 3 Current address: Dipartimento di Chimica, Universit´ a di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy. interesting properties, such as high positive magnetostriction (in Fe 77.5 Si 7.5 B 15 amorphous microwires, λ ∼ 3 × 10 −5 ), very soft magnetic character, nearly non-hysteretic behaviour and magnetic bistability [13, 14]. The magnetic bistability in Fe 77.5 Si 7.5 B 15 microwires may be understood as the result of a peculiar domain structure associated with strong magnetoelastic and shape anisotropies and the absence of a magnetocrystalline term due to the amorphous nature of the samples [15–17]. The stresses frozen in during the fabrication process and resulting from different thermal expansion coefficients of coating and nucleus give rise to this strong magnetoelastic term, which together with shape anisotropy results in a strong uniaxial anisotropy. This results in a peculiar domain structure, consisting of an inner cylindrical core that runs along most of the microwire’s length, with magnetization parallel to the axis (macroscopic monodomain), and a surface domain structure consisting 0022-3727/08/095005+07$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK