Sub‐20 nm Magnetic Dots with Perpendicular Magnetic Anisotropy (original) (raw)
Related papers
2010
Patterned arrays of ferromagnetic nanoparticles of Co, Ni, and Fe 50 Co 50 have been synthesized from their ultrathin metal films on SiO 2 substrate by nanosecond laser-induced self-organization. The morphology, nanostructure, and magnetic behavior of the nanoparticle arrays were investigated by a combination of electron, atomic force, and magnetic force microscopy techniques. Transmission electron microscopy investigations revealed a granular polycrystalline nanostructure, with the number of grains inside the nanoparticle increasing with their diameter. Magnetic force measurements showed that the magnetization direction of the Co and Ni nanoparticles was predominantly out-of-plane while those for the Fe 50 Co 50 alloy was in the plane of the substrate. This difference in behavior is due to the dominating influence of magnetostrictive energy on the magnetization as a result of residual thermal strain following fast laser processing. Since the magnetostriction coefficient is negative for polycrystalline Co and Ni, and positive for Fe 50 Co 50 , the tensile residual strain forces the magnetization direction of the negative magnetostriction materials out-of-plane and the positive magnetostriction materials in-plane. This demonstrates a cost-effective non-epitaxial technique for the fabrication of patterned arrays of magnetic nanoparticles with tailored magnetization orientations.
Patterned magnetic media from self-assembly template methods
Using lyotropic liquid crystalline phases and self-assembly from colloidal suspensions of polystyrene latex spheres, well-ordered, nanostructured templates were prepared. The results of electrochemical deposition of magnetic metals and alloys in the voids of these templates are presented. This technique has enabled the creation of magnetic nanostructures with 3Dachitectures on length scales 4 nmÀ1 mm. Changes in coercive field, by more than an order of magnitude were found, dominated by the effects of domain wall pinning. Clear transverse magnetisation suggests Bloch type of the domain walls. The in-plane component of the magnetic field drives the magnetic hysteresis. The templated electrodeposition technique offers the potential of a low-cost preparation method for sub-micron patterned magnetic media.
Self-Organized Hexagonal Patterns of Independent Magnetic Nanodots
Advanced Materials, 2007
Self-organized hexagonal nanodot patterns can be formed by ion bombardment on semiconductor surfaces. Here it is shown how this method can be applied to the production of ordered nanostructures of almost any type of material by transferring the pattern originally developed on an appropriate formation layer to an intercalated thin film. Our experiments using Co as the buried material have resulted in the appearance of large-area, isotropic arrays of magnetic nanoparticles. The same procedure could be used with other nonmagnetic buried layers, whether metallic, semiconducting, or heterostructure.
Large-area patterned magnetic nanostructures by self-assembling of polystyrene nanospheres
MRS Proceedings, 2012
Magnetic nanostructures are attracting considerable interest due to their unique properties and potential applications. There are various challenges associated with the fabrication of highly ordered large area magnetic nanostructures and the understanding of their magnetization reversal processes. This review focuses on the use of the deep ultraviolet lithography technique in fabricating arrays of magnetic nanostructures of varying geometrical parameters over a large area. Using resolution enhancement techniques such as alternating phase shift and chrome-less phase shift masks (PSMs), arrays of ferromagnetic nanostructures with lateral dimensions below the conventional resolution limit have been fabricated. Comprehensive investigation of the relationship between the swing amplitude and the pattern size using alternating PSM lithography is presented. Double patterning and double exposure with shifts are used to significantly improve the pattern density and manipulate the magnetic nanostructures. In addition, results of systematic investigations of evolution of magnetic spin states, in-plane anisotropy and magnetostatic interaction in arrays of elongated Ni 80 Fe 20 rings and their derivatives are presented. The magnetization reversal mechanism, the switching field distributions and the transition fields between different magnetic configurations are found to be strongly dependent on the inter-ring spacing, film thickness and any missing segments of the ring. A comprehensive investigation of the spin states and magnetic anisotropy in magnetic antidot nanostructures is also presented. The detailed magnetization reversal reveals a very strong pinning of domain walls in the vicinity of anti-structures, the strength of which was found to be strongly dependent on the anti-structure geometry and field orientation.
Nanopatterned Magnetic Metal via Colloidal Lithography with Reactive Ion Etching
Chemistry of Materials, 2004
Two-dimensional patterned surfaces have attracted great attention because of their potential uses in biochips and sensors, 1 electronic devices, 2 magnetic recording devices, 3 photonic crystals, 4 and templates for novel materials. 5 Various nanofabrication techniques have been used to construct such patterned surfaces, including soft lithography 6 and laser interference lithography. 7 Several self-assembly techniques employing block copolymers 8 and colloidal particles have also been used to create 2D patterns. 9 Specifically, well-organized 2D particle arrays are of practical significance for applications in soft lithography, 10 microlenses, 11 carbon nanotube arrays, 12 and colloidal lithography (CL). In CL, colloidal arrays are used as lithographic masks or templates to fabricate nanostructures. 13 CL has several advantages: it is an inexpensive, inherently parallel, high-throughput nanofabrication technique. 13 Primarily, single and double layers of colloidal particles have been used in CL as templates for patterned polymers and metals. In general, interstices between the particles were used for infiltration of the polymers and metals. A close-packed colloidal assembly usually forms interstices with hexagonal shapes in a single layer or triangular shapes in a double layer.
Lithography and self-assembly for nanometer scale magnetism
Microelectronic Engineering, 2002
The limits to scaling the relevant physical dimensions required to increase the areal density of magnetic storage devices will be reached soon, if the storage density continues to double annually. Two approaches to overcoming the limit of the minimum particle size required for thermal stability are presented. In the first approach, a narrow particle size distribution is produced using self-assembled layers of magnetic Fe-Pt nanoparticles. The very narrow particle size distribution offers the potential for increased storage density by utilizing a smaller mean particle size and ultimately storage of one bit per individual nanoparticle. The second approach involves patterned magnetic Co-Cr-Pt nanostructures produced using a focused ion beam, which offers the possibility of single bit per island storage on thermally stable sub-100-nm islands.
Controlled Self-Assembly for High-Resolution Magnetic Printing
Small, 2014
High-resolution patterning technology capable of massproducing large patterned areas is very useful for producing electronic devices and biochips. As an alternative to improve on existing patterning technology, diverse printing techniques have been extensively studied. However, the resolution achievable using printing technology is typically limited to 20-30 μ m. In particular, with the carbon nanomaterials that have been used in organic electronic devices, it is diffi cult to print patterns with line widths of less than about 70 μ m. In general, metal nanoparticles should be sintered at high temperatures when used as ink materials, and inkjet printing of carbon nanomaterials produces only thin patterns after one printing operation, making repeated printing (often dozens of times) necessary. This decreases the productivity of these methods signifi cantly. Here, we demonstrate that a controlled magnetic fi eld can create a nanoparticle pattern with a minimum line width of 10 μ m on a fl exible substrate. The spatial distribution of the magnetic fi eld determining the shape of the printed patterns of superparamagnetic nanoparticles was adjusted by changing the direction of the external magnetic fi eld and the arrangement of the patterned nickel structures in the magnetic mask. This magnetic printing method has also been successfully used to print conductive patterns consisting of copper or carbon nanomaterials.
Physical Review Letters, 2002
The self-assembly of iron dots on the insulating surface of NaCl(001) is investigated experimentally and theoretically. Under proper growth conditions, nanometer-scale magnetic iron dots with remarkably narrow size distributions can be achieved in the absence of a wetting layer. Furthermore, both the vertical and lateral sizes of the dots can be tuned with the iron dosage without introducing apparent size broadening, even though the clustering is clearly in the strong coarsening regime. These observations are interpreted using a phenomenological mean-field theory, in which a coverage-dependent optimal dot size is selected by strain-mediated dot-dot interactions.