Effects of bar length on switching field of nanoscale nickel and cobalt bars fabricated using lithography

Abstract

The switching behavior of isolated nanoscale nickel and cobalt bars, which were fabricated using electron-beam lithography, was studied as a function of bar length. The bars have a 35 nm thickness, a 100 nm width, and a length varying from 200 nm to 5 m. Magnetic force microscopy showed that except for the Ni bars with a length equal to or less than 250 nm, all other as-fabricated bars were single domain. Unlike the bar width dependence, the switching field of the single-domain bars was found to first increase with the bar length, then decrease after reaching a peak. The peak switching field and the corresponding bar length are 640 Oe and 1 m for Ni and 1250 Oe and 2 m for Co, respectively. The nonmonotonic length dependence suggests that the magnetization switching may be quasicoherent in the short bars and incoherent in the long bars, and that the exchange coupling is much stronger in Co bars than in Ni bars. Furthermore, the switching field of 1-m-long Co bars was found to increase monotonically as the bar width decreases, reaching 3000 Oe at a 30 nm width.

Micromagnetic studies of cobalt microbars fabricated by nanoimprint lithography and electrodeposition

“…Thin cobalt bars and ellipses [2][3][4][5][6][7][8], and circular dots [9][10][11][12][13], are among the common shapes that have been a subject of micromagnetic investigations. In studies of magnetization reversal in cobalt bars, the most common geometry used were the bars with square corners [2,4,[6][7][8].…”

“…It was shown by micromagnetic modeling [14] properties, and that an alternative shape has to be found in order to ensure the reproducible switching. Among various techniques for preparation of ferromagnetic elements, sputtering [2,10,13], evaporation [3,4,6,7,9] and molecular beam epitaxy [8], the electrochemical deposition has found limited application, mostly for production of elements with perpendicular magnetization [15][16][17][18][19][20].…”

Magnetic domain states in nano-sized Co nuclei electrodeposited onto monocrystalline silicon

“…These nanostructures present a unique magnetic behavior, the socalled mesoscopic magnetism, which provides a link between magnetism at molecular level and the macroscopic scale [2]. In particular, below a critical dimension, ferromagnetic nanostructures reveal a stable single-domain (SD) configuration without the assistance of an external field [3,4]. When fabricated onto semiconductor substrates, SD nano-magnets can provide novel applications such as spindependent electronics, magnetic storage and integrated sensors.…”

“…At present, magnetic nanostructures of different shapes (dots, bars, pillars, etc) are obtained by techniques like ion implantation, sputtering and metal evaporation [1][2][3][4][5][6][7][8][9][10][11]. Electrodeposition (ED) on the other hand is a wellestablished technology, which can be a complement to the more expensive high vacuum methods.…”

Detection of a single magnetic dot using a Planar Hall sensor

“…Direct coupling between the Co magnetic dots and the sensing layer underneath it takes place as the coupling length of Co is 15.2 nm [6]. When the external field is at the negative saturation value (Fig.…”