Manipulation of fast magnetization switching in magnetically bistable microwires through the magnetoelastic anisotropy

Abstract

IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, SpainWe studied effect of magnetoelastic anisotropy and role of defects on domain wall (DW) dynamics andremagnetization process of magnetically-bistable microwires. We manipulated the magnetoelastic anisotropychanging the ratio between the metallic nucleus diameter and glass coating thickness and applying the tensilestresses. Application of stresses resulted in increase of the switching field and decrease of the DW velocity, v. Therole of defects existing in magnetically bistable microwires is related with nucleation of new reversed domains.Abrupt jumps on v(H) dependences correlate with defects existing in microwires. Annealing allows considerablyincrease DW velocity, enhances the magnetic field range of single DW propagation regime and domain wall mobility.Key words: amorphous microwires, domain wall dynamics, magnetic anisotropy1. IntroductionStudies of domain wall (DW) propagation in thinmagnetic wires prepared by different methods attractedgrowing attention during last few years [1, 2]. Maintechnological interest is related with proposedapplications involving the information storage,magnetic sensors and logics. For aforementionedapplications the DW speed and the ways for the DWdynamics manipulation are essentially relevant.Reported DWs propagation can be driven by themagnetic field as well as by the electric current flowingthrough the sample. The DW velocity is determined bythe magnetic field value as well as by the shape anddimensions of the wires [1, 3-6]. Thus, for amorphousmicrometric wires with circular cross section fastest DWvelocity (exceeding 1000 m/s) have been reported [7,8].Additionally the DW velocity, v, depends on themagnetoelastic anisotropy depending on themagnetostriction constant value as well as on theinternal or applied stress [9]. On the other hand, forcontrolling the DWs dynamics in thin wires (either withrectangular or cylindrical cross-section), fewmechanisms involving the DW injection, creation ofartificial defects and inhomogeneities, controllable DWcollision etc have been reported [9, 10].Studies of glass-coated microwires withferromagnetic nucleus attracted considerable attentionwithin last few years owing to their reduced dimensionsand unusual soft magnetic properties such asspontaneous magnetic bistability, Giantmagnetoimpedance effect and high magneticpermeability. Magnetic bistability is related with largeand single Barkhausen jump observed in amorphousmicrowires with positive magnetostriction constant isparticularly interesting for studies of the DWpropagation within the inner core of microwire [5-7, 11].On the other hand giant magneto-impedance, GMI,effect and extremely soft magnetic properties can beuseful for magnetic sensors applications [12, 13].Abovementioned magnetic bistability observed inamorphous glass-coated microwires with positivemagnetostriction constant is related with fastmagnetization switching of a large single axiallymagnetized domain by fast DW propagation of a singleDW [5-8, 11, 13]. Therefore these microwires are uniquematerial allowing studying the magnetization dynamicsof a single DW in a cylindrical micrometric wire.Appearance of such peculiar domain structureconsisting of a large single axially magnetized domainsurrounded by outer radially magnetized shell isdetermined by the stresses arising during rapidsolidification of composite thin wire [5, 13-17]. Thestrength of these stresses originated from the differencein thermal expansion coefficients of the metal and glassis determined by the volumes of metallic nucleus andglass coating [14-16]. Consequently the magneticsoftness of glass-coated microwires is determined by themagnetoelastic anisotropy originated from thecomposite character being also depending on themetallic nucleus composition and ratio between themetallic nucleus diameter, and total microwirediameter.Consequently fast magnetization switching ofmicrowires is related with the propagation of the singlehead-to head DW along the wire.Recently we reported, that the samplesinhomogeneities, observed through the measurementsof the distribution of the local nucleation fields, H