Synthesis and characterization of nanorods for magnetic rotational spectroscopy

Abstract

Magnetic rotational spectroscopy (MRS) with magnetic nanoprobes is a powerful method for in-situ characterization of minute amounts of complex fluids. In MRS, a uniformly rotating magnetic field rotates magnetic micro-or nano-probes in the liquid and one analyzes the features of the probe rotation to extract rheological parameters of liquids. Magnetic properties of nanoprobes must be well characterized and understood to make results reliable and reproducible. Ni and Co nanorods synthesized by electrochemical template synthesis in alumina membranes are discussed in applications to MRS. We employ alternating gradient field magnetometry, X-ray diffraction, and magnetic force microscopy to evaluate and compare properties of these nanorods and study their performance as the MRS probes. It is shown that nickel nanorods do not seem to violate any assumptions of the MRS rigid dipole theory, while cobalt nanorods do.

Ferromagnetic Nanorods in Applications to Control of the In‐Plane Anisotropy of Composite Films and for In Situ Characterization of the Film Rheology

“…c) Reaction time was 25 min and d) reaction time was 60 min. Reproduced with permission . Copyright 2015, American Institute of Physics.…”

“…Magnetic nanorods of 100–200 nm diameter can be covered with polymers to prevent their agglomeration . One can generate Ni, Co, permalloy, and other metallic nanorods and nanotubes . As an example, the Scanning Electron Microscope (SEM) image shown in Figure shows nickel and cobalt nanorods produced in our laboratory.…”

“…The template grown nanorods and nanotubes exhibit ferromagnetic order, with a distinguishable hysteresis loop ( Figure ). The model of coherent rotation of magnetization vector associated with the rigid dipole model of the nanorod does not explain the hysteresis loops observed in experiments . As evidenced from the analysis of magnetic microstructure of nanorods with magnetic force microscopy and X‐ray diffraction, the nanorods are composed of multiple domains separated by grain boundaries.…”

“…The rod‐like ferromagnetic nanoparticles deserve a special attention because of their specific anisotropic interactions favoring uniaxial magnetic anisotropy of alignment of spins along the nanorod axis . This type of anisotropic ordering is attractive for the different high‐tech applications, in particular, in medical, sensoric, optofluidic, and microrheological engineering.…”

“…MRS takes advantage of a distinguishable behavior of rotating magnetic tracers as the frequency of applied rotating field changes. Unlike many methods based on the analysis of small oscillations, which are difficult to interpret when the film is very thin, MRS with magnetic nanorods enjoys analysis of full revolutions of magnetic tracers …”