Flux measurements on ferromagnetic microprobes by electron holography

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

An iron filled carbon nanotube (FeCNT), a 10-40 nm ferromagnetic nanowire enclosed in a protective carbon tube, is an attractive candidate for a magnetic force microscopy (MFM) probe as it provides a mechanically and chemically robust, nanoscale probe. We demonstrate the probe's capabilities with images of the magnetic field gradients close to the surface of a Py dot in both the multi-domain and vortex states. We show the FeCNT probe is accurately described by a single magnetic monopole located at its tip. Its effective magnetic charge is determined by the diameter of the iron wire and its saturation magnetization 4πM(s) ≈ 2.2 × 10(4)G. A magnetic monopole probe is advantageous as it enables quantitative measurements of the magnetic field gradient close to the sample surface. The lateral resolution is defined by the diameter of the iron wire and the probe-sample separation.

Off-axis electron holography of magnetic nanowires and chains, rings, and planar arrays of magnetic nanoparticles

A selection of recent results illustrating the application of off-axis electron holography to the study of magnetic microstructure in closely-spaced nanoparticles and nanowires is reviewed. Examples are taken from the characterization of FeNi nanoparticle chains, Co nanoparticle rings, two-dimensional arrays of naturally occurring magnetite crystals in minerals, and single crystalline Co nanowires. Approaches that can be used to separate the magnetic signal of interest from the mean inner potential contribution to the measured holographic phase shift are described, and the spatial and phase resolution that can be achieved are discussed.

Study of the field around magnetic force microscopy probes using electron holography

We have used electron holography to perform quantitative investigations of the leakage flux of thin film tips used as probes in magnetic force microscopy. A method to deduce an arrangement of magnetic domains in a thin magnetic whisker from the knowledge of the stray flux is also described. A simple analytical model of the magnetic properties of the probes allows the extraction of computer images, which simulate the experimental results satisfactory. The reliability of the recorded experimental maps of the magnetic flux arising from these kinds of sensors allows an evaluation of the total flux affecting the sample and the calculation of the magnetic field profile along the tip axis.

MAGNETIC FORCE MICROSCOPY

▪ Abstract  This review on magnetic force microscopy does not provide an exhaustive overview of the past accomplishments of the method but rather discusses the present state of the art. Magnetic force microscopy is a special mode of noncontact operation of the scanning force microscope. This mode is realized by employing suitable probes and utilizing their specific dynamic properties. The particular material composition of the probes and the dynamic mode of their operation are discussed in detail. The interpretation of images acquired by magnetic force microscopy requires some basic knowledge about the specific near-field magnetostatic interaction between probe and sample. The general magnetostatics as well as convenient simplifications of the general theory, which often can be used in practice, are summarized. Applications of magnetic force microscopy in the magnetic recording industry and in the fundamental research on magnetic materials are discussed in terms of representative examples. An important aspect for any kind of microscopy is the ultimately achievable spatial resolution and inherent restrictions in the application of the method. Both aspects are considered, and resulting prospects for future methodical improvements are given.