Magnetic force microscopy of single-domain cobalt dots patterned using interference lithography (original) (raw)

Magnetic force microscopy observations of the magnetic behavior in Co–C nanodot arrays

Journal of Applied Physics, 2002

The nanomagnetic behavior of Co-C nanodot arrays was investigated by magnetic force microscopy ͑MFM͒ and an alternative gradient force magnetometer. The direction of the easy axis can be observed directly with MFM by comparing the saturated magnetization state and the remanent magnetization state. Interaction of the domain wall with local defects was observed by field dependent MFM measurements. Some types of defects that can pin domain wall movement were identified.

Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy

Nature materials, 2004

The use of magnetic nanoparticles in the development of ultra-high-density recording media is the subject of intense research. Much of the attention of this research is devoted to the stability of magnetic moments, often neglecting the influence of dipolar interactions. Here, we explore the magnetic microstructure of different assemblies of monodisperse cobalt single-domain nanoparticles by magnetic force microscopy and magnetometric measurements. We observe that when the density of particles per unit area is higher than a determined threshold, the two-dimensional self-assemblies behave as a continuous ferromagnetic thin film. Correlated areas (similar to domains) of parallel magnetization roughly ten particles in diameter appear. As this magnetic percolation is mediated by dipolar interactions, the magnetic microstructure, its distribution and stability, is strongly dependent on the topological distribution of the dipoles. Thus, the magnetic structures of three-dimensional assembli...

Nanoimprint lithography of high-density cobalt dot patterns for fine tuning of dipole interactions

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2001

A trilayer nanoimprint process was used to fabricate high-density Co dot arrays. It is shown that choosing hybrane as the top layer resist gives better dimensional control of the replicated patterns compared to PMMA. By adjusting the etching time in the transfer process the dot sizes could be tailored in a wide range. The fabricated dot arrays with different sizes and period have then been studied by magneto-optic and magnetic-force microscopy measurements. The magnetization reversal was found to occur through vortex nucleation/annihilation. Dipolar interactions were clearly identified both in arrays with constant dot diameter and variable period and in arrays with fixed period and variable dot diameters. In the case of closely packed dots vortex chain structures along the field direction can be formed as a consequence of a nucleation cascade process.

Magnetic properties of large aspect ratio Co dots electrodeposited on prestructured silicon substrates

Journal of Magnetism and Magnetic Materials, 2005

A silicon substrate, pre-structured by focused ion beam (FIB), is used for selective electrodeposition of cylindrical cobalt nanodots with a large aspect ratio of depth to diameter of 2. These nanostructures are characterised by magnetic force microscopy (MFM) and ferromagnetic resonance (FMR). Cobalt dots grown in the pulsed mode are single domain in the remnant state with an easy magnetization perpendicular to the substrate. On the contrary, some of the dots grown, in the continuous mode, present a Co cap on top, which leads to the formation of magnetic vortices with an in-plane magnetization component.

Experimental magnetic study and evidence of the exchange bias effect in unidimensional Co arrays produced by interference lithography

Solid State Communications, 2007

A simple process for fabricating submicrometric magnetic arrays employing interference lithography, sputtering deposition and lift-off processes is proposed and demonstrated. The magnetic properties of cobalt (Co) arrays were measured and compared with those of a continuous Co magnetic film. The results show a dependence of the hysteresis curve on the orientation of the field as regards the array, which is correlated with the anisotropy of the structures and a dependence of the coercive field on the periodicity of the arrays. Moreover, an exchange bias effect was observed, which is ascribed to a ferromagnetic/antiferromagnetic (FM/AFM) coupling between Co and a thin surface cobalt oxide (CoO) layer.

Formation of magnetic dots in an ultrathin Co film forced by a patterned buffer

EPL (Europhysics Letters), 2010

The novel method for fabricating magnetic dots reported in this work exploits the dependence of the magnetic anisotropy of an ultrathin Co film on its thickness and on the type of the buffer layer. A patterned buffer prepared as self-assembled Au islands with a lateral size of several hundred nanometres grown on a Mo film surface induces mono-domain dots magnetized perpendicularly to the film plane in the epitaxial Co layer. Polar magneto-optical Kerr magnetometry and magnetic force microscopy have been used to investigate the magnetization reversal of the dots. Nucleation of the reversed magnetic domain followed by the unpinned movement of domain walls is discussed as a possible mechanism responsible for magnetization switching.

Growth and micromagnetism of self-assembled epitaxial fcc(111) cobalt dots

Journal of physics. Condensed matter : an Institute of Physics journal, 2013

We develop the self-assembly of epitaxial submicrometer-sized face-centered-cubic (fcc) Co(111) dots using pulsed laser deposition. The dots display atomically flat facets, from which the ratios of surface and interface energies for fcc Co are deduced. Zero-field magnetic structures are investigated with magnetic force and Lorentz microscopies, revealing vortex-based flux-closure patterns. A good agreement is found with micromagnetic simulations.

Magnetic nanostructure fabrication by soft lithography and vortex-single domain transition in Co dots

Journal of Magnetism and Magnetic Materials, 2002

Micron/nano scale Co dot and wire arrays have been fabricated by soft lithography patterning with a resolution of 100 nm. Magneto-optic Kerr effect magnetometry combined with micromagnetic calculation is used to study, in detail, the vortex-single domain transition in the Co dots. A metastable single-domain state, which is stabilized by a local minimum energy induced by vortex nucleation, is demonstrated. r

Individually grown cobalt nanowires as magnetic force microscopy probes

Applied physics letters, 2018

AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires from simple salt solutions using the Directed Electrochemical Nanowire Assembly method. Nanowire diameters were tuned from the submicron scale to 40 nm by adjusting the AC voltage frequency and the growth solution concentration. The structural properties of the nanowires, including shape and crystallinity, were identified using electron microscopy. Hysteresis loops obtained along different directions of an individual nanowire using vibrating sample magnetometry showed that the magnetocrystalline anisotropy energy has the same order of magnitude as the shape anisotropy energy. Additionally, the saturation magnetization of an individual cobalt nanowire was estimated to be close to the bulk single crystal value. A small cobalt nanowire segment was grown from a conductive atomic force microscope cantilever tip that was utilized in magnetic force microscopy (MFM) imaging. The fabricated MFM ti...