Research articles Free and forced Barkhausen noises in magnetic thin film based cross-junctions Amir Elzwawy a,b , Artem Talantsev a,c,d,⇑ , CheolGi Kim a,⇑ a Department of Emerging Materials Science, DGIST, Daegu 42988, Republic of Korea b Ceramics Department, National Research Centre, 12622 El-Bohouth Str., Cairo, Egypt c Institute of Problems of Chemical Physics, 142432, Chernogolovka, Moscow, Russia d Tambov State Technical University, 392000 Tambov, Russia article info Article history: Received 6 February 2018 Received in revised form 10 March 2018 Accepted 17 March 2018 Available online 19 March 2018 Keywords: Magnetic thin films Magnetization switching Anisotropic magnetoresistance Planar Hall effect Barkhausen noise abstract Barkhausen noise, driven by thermal fluctuations in stationary magnetic field, and Barkhausen jumps, driven by sweeping magnetic field, are demonstrated to be effects of different orders of magnitude. The critical magnetic field for domain walls depinning, followed by avalanched and irreversible magne- tization jumps, is determined. Magnetoresistive response of NiFe/M/NiFe (M = Au, Ta, Ag) trilayers to sta- tionary and sweeping magnetic field is studied by means of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) measurements. Thermal fluctuations result in local and reversible changes of magnetization of the layers in thin film magnetic junctions, while the sweeping magnetic field results in reversible and irreversible avalanched domain motion, dependently on the ratio between the values of sweeping magnetic field and domain wall depinning field. The correlation between AMR and PHE responses to Barkhausen jumps is studied. The value of this correlation is found to be dependent on the a angle between the directions of magnetic field and current path. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction Magnetic thin films are widely used in magnetoresistive devices for magnetic field detection [1–4]. Wide operating temperature ranges and competitive sensitivities to low magnetic fields make magnetoresistive sensors gain new and new areas of application in magnetic field detection and magnetic nanoparticles detection in biotechnology [2,3]. Generally, single domain state of these films is required for detection of low magnetic fields. However, magnetic films with stable multi-domain states still remain objects of inter- est, especially in magnetic nanoparticles detection. The stray fields of magnetic particles, deposited on the surface of multi-domain thin film, cause local magnetization reversals in these films. The spatial distribution of these local reversals partially replicates the distribution of nanoparticles on the surface of the film. However, spontaneous domain wall displacement in magnetic films may result in significant difference between the domain distribution inside the film and magnetic particles distribution on the surface of the film. The domain wall motion can be suppressed in different ways, from the biasing by adjacent antiferromagnetic layers [5,6] to the biasing by shape anisotropy of the junctions [7,8]. However, most of these ways result in single domain state of the sensing layer [5–8]. In this work we will demonstrate, that the magnetic field sensitivity of junctions, based on multi-domain magnetic films, is comparable with sensitivities of single domain ones, if the magnetic energy of the film in applied magnetic field is less than energy barrier of domain wall depinning. Direct measurements of sample magnetization allow us to judge about key magnetic parameters of magnetoresistive junc- tion. However, magnetic hysteresis loops of each magnetic layer in the junction, separately, can be recorded only if these loops are separated from each other by exchange bias magnetic fields [9–13]. In case of no exchange bias, or weak bias and partial sepa- ration of magnetic hysteresis loops of the top and bottom layers, direct measurements of magnetization give us just general infor- mation about magnetization reversal in the entire sample, without any respect to the layer, where this reversal occurs. Instead of direct magnetic measurements, the planar Hall effect (PHE) output voltage is sensitive to mutual magnetization direc- tions of layers, because of the contribution of giant magnetoresis- tance (GMR) effect [10]. For example, if there is ferromagnetic coupling between top and bottom ferromagnetic (FM) layers, sep- arated by a nonmagnetic interlayer (NM), the reversal nuclei in bottom layer will be directly under reversal nuclei in the top layer https://doi.org/10.1016/j.jmmm.2018.03.042 0304-8853/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding authors at: Department of Emerging Materials Science, DGIST, Daegu 42988, Republic of Korea (A. Talantsev). E-mail addresses: adt@dgist.ac.kr (A. Talantsev), cgkim@dgist.ac.kr (C. Kim). Journal of Magnetism and Magnetic Materials 458 (2018) 292–300 Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm