Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe

Roadmap on nanoscale magnetic resonance imaging

The field of nanoscale magnetic resonance imaging (NanoMRI) was started 30 years ago. It was motivated by the desire to image single molecules and molecular assemblies, such as proteins and virus particles, with near-atomic spatial resolution and on a length scale of 100 nm. Over the years, the NanoMRI field has also expanded to include the goal of useful high-resolution nuclear magnetic resonance (NMR) spectroscopy of molecules under ambient conditions, including samples up to the micron-scale. The realization of these goals requires the development of spin detection techniques that are many orders of magnitude more sensitive than conventional NMR and MRI, capable of detecting and controlling nanoscale ensembles of spins. Over the years, a number of different technical approaches to NanoMRI have emerged, each possessing a distinct set of capabilities for basic and applied areas of science. The goal of this roadmap article is to report the current state of the art in NanoMRI technologies, outline the areas where they are poised to have impact, identify the challenges that lie ahead, and propose methods to meet these challenges. This roadmap also shows how developments in NanoMRI techniques can lead to breakthroughs in emerging quantum science and technology applications.

Probing electrical properties of individual carbon nanotubes filled with Fe3C nanowires

The electrical properties of individual multiwall carbon nanotubes (CNTs) filled with Fe₃C nanowires (Fe-CNTs) grown by chemical vapor deposition were investigated. The individual Fe-CNTs were measured by two-probe configuration in a scanning electron microscope, in which one probe was used to contact one end of the nanotubes and the other varied its contact position to measure the resistance along the Fe-CNTs. The data suggest that the ferromagnetic nanowires and the CNTs were well connected into a conduction network, and the resistance of the individual Fe-CNTs decreased as the filling rate increased. Analysis shows that the encapsulated ferromagnetic nanowires played a profound part in determining the electrical behavior of individual Fe-CNTs. The results may be useful for understanding of electronic transport of individual Fe-CNTs and applications based on individual Fe-CNTs.

Magnetic imaging using geometrically constrained nano-domain walls

Magnetic nanostructures, as part of hybrid CMOS technology, have the potential to overcome silicon's scaling limit. However, a major problem is how to characterize their magnetization without disturbing it. Magnetic force microscopy (MFM) offers a convenient way of studying magnetization, but spatial resolution and sensitivity are usually boosted at the cost of increasing probe-sample interaction. By using a single magnetic domain wall (DW), confined in a V-shape nanostructure fabricated at the probe apex, it is demonstrated here that the spatial resolution and the magnetic sensitivity can be decoupled and both enhanced. Indeed, owing to the nanostructure's strong shape anisotropy, DW-probes have 2 high and 2 low magnetic moment states with opposite polarities, characterised by a geometrically constrained pinned DW, and curled magnetization, respectively. Electron holography studies, supported by numerical simulations, and in situ MFM show that the DW-probe state can be controlled, and thus used as a switchable tool with a low/high stray field intensity.

Compensation of the magnetic force imaging by scanning directions

It was found that the results of magnetic force microscope (MFM) imaging were different with the probe scanning directions. This paper studied the effect of scanning directions on the MFM imaging, and a method for the distortion compensation was proposed to reduce the errors. In the study, three different scanning directions with the angles of 0°, 45° and 90° were used to measure the magnetic domain structures distributions of magnetic sample. The experimental results have shown that the scanning direction parallel to the magnetic domain structure will cause a minimum phase shift difference and lead to a structure distortion. A method for compensating the distortions was proposed. With this method, the distorted structures were corrected and the effect of scanning directions on the MFM imaging was significantly reduced. This work provides a way for the acquisition of the correct images of magnetic structures using an MFM and the improvement of imaging quality in a wide range of MFM applications.

Signal enhancement in cantilever magnetometry based on a co-resonantly coupled sensor

Cantilever magnetometry is a measurement technique used to study magnetic nanoparticles. With decreasing sample size, the signal strength is significantly reduced, requiring advances of the technique. Ultrathin and slender cantilevers can address this challenge but lead to increased complexity of detection. We present an approach based on the co-resonant coupling of a micro- and a nanometer-sized cantilever. Via matching of the resonance frequencies of the two subsystems we induce a strong interplay between the oscillations of the two cantilevers, allowing for a detection of interactions between the sensitive nanocantilever and external influences in the amplitude response curve of the microcantilever. In our magnetometry experiment we used an iron-filled carbon nanotube acting simultaneously as nanocantilever and magnetic sample. Measurements revealed an enhancement of the commonly used frequency shift signal by five orders of magnitude compared to conventional cantilever magnetometry experiments with similar nanomagnets. With this experiment we do not only demonstrate the functionality of our sensor design but also its potential for very sensitive magnetometry measurements while maintaining a facile oscillation detection with a conventional microcantilever setup.