Nanosized corners for trapping and detecting magnetic nanoparticles

Abstract

We present a device concept based on controlled micromagnetic configurations in a corner-shaped permalloy nanostructure terminated with two circular disks, specifically designed for the capture and detection of a small number of magnetic beads in suspension. A transverse head-to-head domain wall (TDW) placed at the corner of the structure plays the role of an attracting pole for magnetic beads. The TDW is annihilated in the terminating disks by applying an appropriate magnetic field, whose value is affected by the presence of beads chemically bound to the surface. In the case where the beads are not chemically bound to the surface, the annihilation of the TDW causes their release into the suspension. The variation of the voltage drop across the corner, due to the anisotropic magnetoresistance (AMR) while sweeping the magnetic field, is used to detect the presence of a chemically bound bead. The device response has been characterized by using both synthetic antiferromagnetic nanoparticles (disks of 70 nm diameter and 20 nm height) and magnetic nanobeads, for different thicknesses of the protective capping layer. We demonstrate the detection down to a single nanoparticle, therefore the device holds the potential for the localization and detection of small numbers of molecules immobilized on the particle's functionalized surface.

Spin Wave Excitations of the Interacting Two-Dimensional In-Plane Nano-Vortices

“…In small magnetic dots the competition between the exchange and dipolar interactions leads to a rich spectrum of magnetic configurations including vortices [4]. In potential applications of magnetic vortices, which rage from information processing to microwave-frequency multiplication [5][6][7], an important role is played by spin waves. In particular, the lowest mode plays a special role in metastable vortices, in which it becomes a soft mode responsible for the transition to different magnetic configurations [8].…”

Special Modes in Spin Wave Spectra of Two-Dimensional Nanodots

“…Potential applications of magnetic vortices include single magnetic nanoparticle sensing and trapping [8], microwavefrequency oscillators [9], data storage and information processing [10], or frequency multiplication [11].…”

Oersted field assisted magnetization reversal in cylindrical core-shell nanostructures

“…INTRODUCTION Synthesis and characterization of functionalized ferromagnetic nanotubes (FNTs) and planar/cylindrical ferromagnetic nanowires have unveiled interesting physical properties with a direct impact on technological applications, mostly in spintronics and biotechnology fields. In fact, the interplay between their particular aspect ratio and phenomenology makes them suitable for several purposes, for instance, magnetic racetrack memories 1 and logic gates, 2,3 proposed as basic elements for storage and processing of digital information, and further, as devices for trapping and sensing bio-functionalized nanoparticles, 4 and nanoconduits for channeling of protein coated magnetic beads 5,6 in cell recognition and treatment of tumor diseases. Among the lengthened nanoparticles variety, FNTs are becoming very attractive because of the ability of functionalizing differentially their two cylindrical surfaces and the tuning of their dimensions and magnetic phases.…”