Magnetic properties of sub-micrometric Fe-rich wires A. Chizhik a, ⁎, A. Zhukov a, b , J. Gonzalez a a Departamento de Fısica de Materiales, Facultad de Quımica, Universidad del Pais Vasco, UPV/EHU, 1072, 20080 San Sebastian, Spain b IKERBASQUE, Basque Foundation for Science, Alameda Urquijo, 36-5, Plaza Bizkaia, 48011 Bilbao, Bizkaia, Spain abstract article info Available online 31 January 2013 Keywords: Amorphous magnetic wire Magneto-optical Kerr effect Magnetization reversal The investigation of the magnetization reversal has been performed in Fe-rich sub-micrometric glass covered wires of different radiuses. The surface magnetization reversal has been studied using the magneto-optical Kerr effect. The axial tensile stress and torsion stress have been applied during the experiments. Surface hysteresis loop was found to be rectangular because of magnetic bistability. This confirms the existence of the Surface Large Barkhausen Jump in sub-micrometric glass covered wires explained by the magnetization reversal in a large single surface domain. The analysis of the tensile and torsion stresses' transformation of surface hysteresis loop proves that magnetic bistability earlier observed in thicker glass covered microwires exists down to one order decrease of wire's diameter. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The study of the magnetization reversal process in microwires is one of the most important tasks related to the use of magnetic wires in tech- nological devices [1–4]. Up to date the main investigations were performed in glass covered wires of 1 micrometer–100 micrometer scale. Now, following the tendency of the miniaturization of active ele- ments for magnetic sensors we direct our efforts to the studies of the magnetization reversal nano-metric amorphous wires. Basically, it is clear that the cylindrical symmetry and the specific stress distribution induced by the glass covering are the key parameters providing the competitive technological application of the microwires [1]. The idea of the present investigation is to move to the nano-scale maintaining the achieved optimal parameters of micro-wires. Preparation and study of amorphous glass-coated wires of sub- micrometer scale with metallic nucleus diameters ranging between 100 and 900 nm have been recently reported [5]. Now, applying the different types of the stresses, studying the array of the wires, and changing the angle between the direction of the external magnetic field and wire axis, we investigate the main properties of the magne- tization reversal of the nano-scaled glass covered wires. 2. Experimental details The magnetization reversal has been studied in Fe-rich nano- metric amorphous wires (nominal composition Fe 72.75 Co 2.25 B 15 Si 10 ) using a Quantum Design (San Diego, CA, U.S.A.) physical property measurement system (PPMS) and a magneto-optical Kerr effect (MOKE) magnetometer [6]. The longitudinal configuration of MOKE was employed. The intensity of light, reflected from the surface of microwire, was proportional to the axial component of the magneti- zation. A Cu wire was attached at the end of the sample in order to apply tensile stress. Also the torsion stress has been applied during the experiments. A series of the microwires with different values of geometric ratio ρ has been studied (ρ is the ratio of metallic nucleus diameter, d, to total microwire diameter, D): sample No. 1 ρ = 0.04, metallic nucleus radius r = 400 nm, D = 19 μm; sample No. 2 ρ = 0.067, r=700 nm, D=21 μm; and sample No. 3 ρ =0.085, r= 1000 nm, D=21 μm. 3. Results and discussion First, the arrays of glass covered microwires (radius of metallic nu- cleus 500 nm) have been studied using PPMS technique. The result of PPMS magnetic (4 nano-wires array) experiments is presented in Fig. 1. Jumps of magnetization observed in volume are related to the giant Barkhausen jumps [7] associated with the magnetization rever- sal in single microwire as a result of the interaction between the microwires. Obtained results prove that the magnetic behavior of the glass covered wires with such extremely small diameter keeps magnetically bistable behavior and could be considered in the frame of core-shell model. Three jumps occur for 4 wires. The initial jump has the amplitude two times larger than the second and the third jumps. It happens because of collective jumps: the magnetization re- versal occurs in the same magnetic field in two wires. Secondly, results of the magneto-optical studies of the arrays of glass covered nano-wires (radius of metallic nucleus 500 nm) are presented in Fig. 2. During the experiment the array of 10 wires was Thin Solid Films 543 (2013) 130–132 ⁎ Corresponding author. Tel.: +34 943 018611; fax: +34 943 017130. E-mail address: oleksandr.chyzhyk@ehu.es (A. Chizhik). 0040-6090/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tsf.2013.01.060 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf