Anisotropic magnetoresistance of individual CoFeB and Ni nanotubes with values of up to 1.4% at room temperature

Abstract

Magnetic nanotubes (NTs) are interesting for magnetic memory and magnonic applications. We report magnetotransport experiments on individual 10 to 20 μm long Ni and CoFeB NTs with outer diameters ranging from 160 to 390 nm and film thicknesses of 20 to 40 nm. The anisotropic magnetoresistance (AMR) effect studied from 2 K to room temperature (RT) amounted to 1.4% and 0.1% for Ni and CoFeB NTs, respectively, at RT. We evaluated magnetometric demagnetization factors of about 0.7 for Ni and CoFeB NTs having considerably different saturation magnetization. The relatively large AMR value of the Ni nanotubes is promising for RT spintronic applications. The large saturation magnetization of CoFeB is useful in different fields such as magnonics and scanning probe microscopy using nanotubes as magnetic tips.

Imaging magnetic vortex configurations in ferromagnetic nanotubes

“…These templates are grown by molecular beam epitaxy on a Si (111) substrate using Ga droplets as catalysts [28]. For the CoFeB NTs, CoFeB is then magnetron-sputtered on the NWs, producing an amorphous and homogeneous 30-nm-thick shell [31].…”

“…Scanning electron micrographs (SEMs) of the 19 CoFeB and 25 permalloy (Py) NTs studied [26] reveal continuous surfaces, which are free of detectable defects and whose roughness is less than 5 nm. The fabrication process and choice of materials avoids magneto-crystalline anisotropy [27][28][29], although recent magnetotransport experiments suggest that a growth-induced magnetic anisotropy may be present in the CoFeB NTs [30]. DCM measurements of NTs from the same growth wafers as used here provide μ 0 M S = 1.3 ± 0.1 T and 0.8 ± 0.1 T for the CoFeB [31] and Py [32] NTs, respectively, where μ 0 is the permeability of free space.…”

Observation of end-vortex nucleation in individual ferromagnetic nanotubes

“…The amorphous and homogeneous CoFeB shell is magnetron sputtered onto template GaAs NWs [27], which are grown by molecular beam epitaxy on a Si (111) substrate using Ga droplets as catalysts [28]. During CoFeB deposition, a wafer of upright and well-separated GaAs NWs is mounted with a 35…”

Magnetic Nanowires and Nanotubes

“…Another common technique is vapour-liquidsolid (VLS) growth of semiconducting vertical wires from a catalyst, e.g., GaAs wires on Si substrate (Fig. 2c) from a Ge droplet catalyst (Rüffer et al 2014, Garcia Núñez et al 2018). Related to their crystal structure and orientation, these can have a hexagonal or other non-circular cross-section.…”

“…This way the reaction is self-limiting, both precursors react only at the surface of the sample, and sufficient time can be provided for diffusion. Therefore, ALD provides a conformal coating of high aspect ratio pores without clogging their inlet (Daub et al 2007), and similarly rods (Rüffer et al 2014). Thus it is very suitable for nanotube fabrication (Fig.…”