Fig 5 - uploaded by Andreas Michels
Content may be subject to copyright.
Manufacturing process of a perpendicular magnetic storage medium by magnetic field directed self-assembly. (a) Schematic topview of a perpendicular magnetic storage medium master substrate which is a prerequisite for high throughput mass production. A cross-sectional view of the marked rectangular frame in (a) is shown in (b). (b) Litho- graphically generated high permeability (high μ r ) tracks. The buffer layer enables to lift
Source publication
Magnetic-field-assisted self-assembly of magnetic dipole moment carrying iron nanoparticles is shown to result in the formation of magnetic and mechanically stiff nanoscale rods. The cooperative behavior of an ensemble of such rods and bundles thereof exhibits self-organized pattern formation on different length scales. Pattern formation on large l...
Context in source publication
Context 1
... of rods, and shape anisotropy -which may become much larger than the intrinsic anisotropies particularly in nanostrucutres -, as well as material selection would allow to tailor the key parameter of magnetic recording media [5,32,33]. Figure 5 illustrates the two-step process suggested to prepare nanoscale perpendicular magnetic storage media. ...
Similar publications
Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and elec...
Ratchets are devices able to rectify an otherwise oscillatory behavior by
exploiting an asymmetry of the system. In rocking ratchets the asymmetry is
induced through a proper choice of external forces and modulations of nonlinear
symmetric potentials. The ratchet currents thus obtained in systems as
different as semiconductors, Josephson junctions,...
Simulation of hexagonal pattern formation of ferrofluid in magnetic field has been performed using a finite element method. Based on simulation result, a new mechanism involving ‘active rings’ is proposed to explain the generation of new peaks. Hexagonal nature of the pattern is shown to be originated from the intersections of these active rings. E...
Despite their practical and academic relevance, studies of interfacial pattern formation in confined magnetorheological (MR) fluids have been largely overlooked in the literature. In this work, we present a contribution to this soft matter research topic and investigate the emergence of interfacial instabilities when an inviscid, initially circular...
We establish the existence of spatially localised one-dimensional free surfaces of a fer-rofluid near onset of the Rosensweig instability, assuming a general (nonlinear) magnetisa-tion law. It is shown that the ferrohydrostatic equations can be derived from a variational principle that allows one to formulate them as an (infinite-dimensional) spati...
Citations
... Therefore, since the MNRs are free to rotate, the magnetization of nanorods in the Fig. 3 (b) originates from the response of magnetic moments to the AC magnetic field through both Neel and Brown mechanisms. The role of Brown relaxation in the magnetic response of the MNRs, which is strongly aspect ratiodependent, have been demonstrated in previous results [53,54]. ...
Anyone clicking on this link before May 16, 2024 will be taken directly to the final version of our article on ScienceDirect, which they are welcome to read or download. No sign up, registration or fees are required.
https://authors.elsevier.com/a/1iqQK15KgbRpO0
... In this regard, nanomagnets offer interesting physical properties showing the potential to fulfill such demands. 1,2 The rapid advances in nanofabrication achieved in the last decades have enabled the exploration of a great variety of magnetic nanostructures for a myriad of applications ranging from magnetic recording 3,4 to clinical applications. In the particular case of biomedical applications, the suitability of nanomagnets lies in two main facts. ...
... In this work, we use a peapod-like model to simulate the rigid magnetic rod. Such a model was already considered experimentally 24 and numerically. 15,16,22 We aim to explore the interplay between the structure formation and the translational and rotational dynamics under the influence of an external field. ...
... The quantities of interest are averaged over more than 10 6 time-steps. The beads in the rods have the same dipole moment whose magnitude we set as m* = 4.4, estimated from experiments at room temperature (T E 293 K) using iron nanoparticles 24 with saturation magnetization M s (Fe) = 1700 kA m À1 and radius r E5 nm. Regarding the driving field, we consider B*(t) within the range 10 r B* r 50, which is related to the experimental range 33 mT r B r 165 mT at room temperature. ...
... Experimental values for the magnetic fields are of the order of 0.1 T, 16 but ferrofluids are susceptible already to B o 10 mT. 24 Regarding the frequency, we use values within the range 5 r o* r 30, which corresponds to the actual range 0.8 GHz r o r 4.8 GH, for the values of temperature and radius of the particles mentioned earlier and density 7.874 g cm À3 . Such frequencies are far larger than the usual ones used in field-driven experiments, o E 10 À1 -10 2 Hz. ...
We investigate a two-dimensional system of magnetic colloids with anisotropic geometry (rods) subjected to an oscillating external magnetic field. The structural and dynamical properties of the steady states are analyzed, by means of Langevin Dynamics simulations, as a function of the misalignment of the intrinsic magnetic dipole moment of the rods with respect to their axial direction, and also in terms of the strength and rotation frequency of an external magnetic field. The misalignment of the dipole relative to their axial direction is inspired by recent studies, and this is extremely relevant in the microscopic aggregation states of the system. The dynamical response of the magnetic rods to the external magnetic field is strongly affected by such a misalignment. Concerning the synchronization between the magnetic rods and the direction of the external magnetic field, we define three distinct regimes of synchronization. A set of steady states diagrams are presented, showing the magnitude and rotation frequency intervals in which the distinct self-organized structures are observed.
... In this work, we use a peapod-like model to simulate the rigid magnetic rod. Such a model was already considered experimentally [24] and numerically [15,16,22]. We aim to explore the interplay between the structure formation and the translational and rotational dynamics under the influence of an external field. ...
... The quantities of interest are then averaged over more than 10 6 time steps. All the beads from all rods have the same dipole moment whose magnitude we set as µ * = 4.4 which was estimated based on experiments at room temperature (T ≈ 293K) using iron nanoparticles [24] with saturation magnetization M s (F e) = 1700 kA/m and the radius of the particles r ≈ 5 nm. For external magnetic fields, we use B * (t) values within the range 10 ≤ B * ≤ 50, which is related to the experimental range 33 mT ≤ B ≤ 165 mT at room temperature. ...
... For external magnetic fields, we use B * (t) values within the range 10 ≤ B * ≤ 50, which is related to the experimental range 33 mT ≤ B ≤ 165 mT at room temperature. Experimental values for the magnetic fields are of the order of 0.1 T [16], but ferrofluids have been found to be susceptible already to B < 10 mT [24]. For the sake of simplification, we are omitting the * superscript hereafter in all dimensionless parameters. ...
We investigate a two-dimensional system of magnetic colloids with anisotropic geometry (rods) subjected to an oscillating external magnetic field. The structural and dynamical properties of the steady states are analyzed, by means of Langevin Dynamics simulations, as a function of the misalignment of the intrinsic magnetic dipole moment of the rods with respect to their axial direction, and also in terms of the strength and rotation frequency of an external magnetic field. The misalignment of the dipole relative to their axial direction is inspired by recent studies, and this is extremely relevant in the microscopic aggregation states of the system. The dynamical response of the magnetic rods to the external magnetic field is strongly affected by such a misalignment. Concerning the synchronization between the magnetic rods and the direction of the external magnetic field, we define three distinct regimes of synchronization. A set of steady states diagrams are presented, showing the magnitude and rotation frequency intervals in which the distinct self-organized structures are observed.
... In this work, we use a peapod-like model to simulate the rigid magnetic rod. Such a model was already considered experimentally [24] and numerically [15,16,22]. We aim to explore the interplay between the structure formation and the translational and rotational dynamics under the influence of an external field. ...
... The quantities of interest are then averaged over more than 10 6 time steps. All the beads from all rods have the same dipole moment whose magnitude we set as µ * = 4.4 which was estimated based on experiments at room temperature (T ≈ 293K) using iron nanoparticles [24] with saturation magnetization M s (F e) = 1700 kA/m and the radius of the particles r ≈ 5 nm. For external magnetic fields, we use B * (t) values within the range 10 ≤ B * ≤ 50, which is related to the experimental range 33 mT ≤ B ≤ 165 mT at room temperature. ...
... For external magnetic fields, we use B * (t) values within the range 10 ≤ B * ≤ 50, which is related to the experimental range 33 mT ≤ B ≤ 165 mT at room temperature. Experimental values for the magnetic fields are of the order of 0.1 T [16], but ferrofluids have been found to be susceptible already to B < 10 mT [24]. For the sake of simplification, we are omitting the * superscript hereafter in all dimensionless parameters. ...
We investigate a two-dimensional system of magnetic colloids with anisotropic geometry (rods) subjected to an oscillating external magnetic field. The structural and dynamical properties of the steady states are analyzed, by means of Langevin Dynamics simulations, as a function of the misalignment of the intrinsic magnetic dipole moment of the rods with respect to their axial direction , and also in terms of the strength and rotation frequency of an external magnetic field. The misalignment of the dipole relative to their axial direction is inspired by recent studies, and this is extremely relevant in the microscopic aggregation states of the system. The dynamical response of the magnetic rods to the external magnetic field is strongly affected by such a misalignment. Concerning the synchronization between the magnetic rods and the direction of the external magnetic field, we define three distinct regimes of synchronization. A set of steady states diagrams are presented , showing the magnitude and rotation frequency intervals in which the distinct self-organized structures are observed.
... We present here a numerical study of the self-assembly of a two dimensional system of stiff peapod-like straight filaments, composed of single magnetic dipolar beads that are rigidly linked one by one. A similar system was studied earlier by experiment [17] and simulations [18,19]. The interaction is given by the superposition of the dipolar fields of each dipole bead. ...
... The percolation transition is related to gelation in attractive-driven colloidal systems. Percolation behavior is also of great relevance in highly connected materials due to the possibility of enhancing the electrical and thermal conductivity [17,26]. In addition, there is a relation with the change of the viscosity in systems with sufficient strong bond strength [27,28]. ...
... Each rod is composed of 3 soft beads having a central point-like dipole which interact via a DSS potential. This model is motivated by recent experimental [17] and theoretical [18,19] studies. A novelty of our system is the misalignment of the dipole moment of the individual beads with respect to the axial axis, opening the possibility of forming complex structures using nonspherical particles [12,[38][39][40]. ...
Based on extensive Langevin Dynamics simulations we investigate the structural properties of a two-dimensional ensemble of magnetic rods with a peapod-like morphology, i.e, rods consisting of aligned single dipolar beads. Self-assembled configurations are studied for different directions of the dipole with respect to the rod axis. We found that with increasing misalignment of the dipole from the rod axis, the smaller the packing fraction at which the percolation transition is found. For the same density, the system exhibits different aggregation states for different misalignment. We also study the stability of the percolated structures with respect to temperature, which is found to be affected by the microstructure of the assembly of rods.
... They quote the possibility of simulate such systems using a special class of magnetic nanorods (MNR) consisting of dipolar beads which are permanently linked to each other composing a stiff chain with internal head-to-tail alignment of the dipole moment (see Fig. 1.8). The first approach shown in Fig. 1.8(a) is based on recent experiments by Birringer et al. [37]. The authors performed a field assisted deposition technique to produce magnetic rods made of iron oxide beads aligned as illustrated in Fig. 1.9. ...
... In this work we present a numerical study of the self-assembly of a two-dimensional system of stiff magnetic rods, composed of single dipolar beads linked one by one through internal head-to-tail alignment. A similar system was used earlier in experiment [37] and simulations [36]. Our motivation to explore in more detail the two-dimensional (2D) situation is driven by the fact that many experiments involving assemblies of colloids are actually done at surfaces and/or thin films [85,86,87,88,89]. ...
... We also study the connectivity properties of the present system. The percolation behavior is of great relevance in highly connected materials due to the possibility of enhancing the electrical and thermal conductivity [94,37]. In general, percolation in polymers plays a fundamental role in properties related to conductivity, because in many cases percolation can be made responsible for electrical switching properties. ...
The self-assembly process of a two-dimensional ensemble of magnetic rods is studied.
The rods are modelled as aligned single dipolar beads, the so-called peapod model. The
system is studied by means of Molecular Dynamics and Langevin Dynamics simulations.
An introduction on soft matter systems, showing their main features and some theoretical
and experimental aspects is first presented. In the following, the computational methods
adopted in the simulations and the mathematical treatment of the system are presented
and discussed. Concerning the results of the thesis, a diversity of self-assembled configu-
rations such as: (1) clusters, (2) percolated and (3) ordered structures are obtained and
characterized with respect to the state of aggregation of the particles and ordering. By
increasing the aspect ratio of the magnetic rods, it is found that in two dimensions the
percolation transition is suppressed. This is opposite to what is observed in similar three
dimensional systems. It is shown that such a behavior is a consequence of geometrical
effects which reduce the mobility of the rods as the aspect ratio of such rods is increased.
Concerning the ordering of the particles in the system, a magnetic bulk phase is found
with local ferromagnetic order and an unusual non-monotonic behavior of the nematic
order is also observed. Based also on extensive Langevin Dynamics simulations, the self-
assembled configurations are studied for the special case where the dipole of the beads
that constitute the rods are misaligned with respect to the rod axis. The misalignment
is zero when the dipole is parallel to the axial axis. It is found that the density required
for the formation of the percolated structure decreases with increasing misalignment of
the dipole. Also, the system exhibits different aggregation states (solid or liquid) for
different misalignment, even when the same density is considered. The stability of the
self-assembled structures are studied with respect to temperature, and it usually increases
with increasing misalignment of the dipoles.
... E m < 0, is attractive, for 0 6 h < 54:09 , E m > 0, is repulsive, for 54:09 < h 6 90 and E m = 0 for h ¼ 54:09 . Consequently, magnetically interacting isotropic (spherical or cubic) magnetic particles align in such a manner as to minimize the overall magnetic charge, like for example in a closed ring or spherical agglomerate [53]. However, the superparamagnetic NPs interact magnetically only under an applied MF and align in its direction ( Fig. 2.7a). ...
... The MF caused by a singledomain MNP can be calculated from the magnetic potential, U d ðrÞ, which results from the surface magnetic charge distribution, r S ¼ M Á n, where n is a unit vector normal to the surface of the magnet. So magnetic charge appears at every point of Ms values, MCA (K u1 ) and shape-anisotropy (K d ) constants of elongated particles (N a = N b = ½ and N c = 0) for basic ferromagnetic metals at room temperature [29,53]. ...
... Their Ms values (Table 3.1) decrease in a row from Fe to Co and Ni, as does the number of unpaired electrons (from 4 to 2), which is the origin of their ferromagnetism (Section 2). They have a uniaxial MCA and considerable shape anisotropy when they are in the form of elongated MNPs [53]. The shape-anisotropy constants of elongated Fe and Ni particles are significantly larger than their MCA constants, while this is not the case for Co with a much larger MCA constant (Table 3.1). ...
Magnetic nanoparticles (MNPs) are of great scientific interest because of the size effect associated with their magnetic properties and, even more so, because of their wide-ranging application potential in technology and biomedicine. In this review we focus on anisotropic MNPs that exhibit (i) elongated shapes and (ii) plate-like shapes. This is because the shape and magnetocrystalline structure induce direction-dependent magnetic properties. Different synthesis strategies enable a spatially defined particle growth or assembly into an elongated shape, while the synthesis of plate-like MNPs is limited to only a few examples, e.g., hexaferrites. The control of interparticle forces is necessary to exploit the specific behaviour of anisotropic MNPs and to fabricate multifunctional materials. The assembly and/or complexation of anisotropic MNPs with other functional entities are the basis for developing direction-dependent and magnetically sensitive properties (e.g., optical, electrical, mechanical, chemical). In the first part, the magnetic properties, relevant magnetic materials and syntheses of anisotropic (in particular, elongated and plate-like) MNPs are reviewed. In the second part, the interparticle interactions, with an emphasis on the development of new, complex materials with specific behaviours, are presented. The potential applications of these new, anisotropic, multi-functional materials with future perspectives are given in the final part.
... This material are used as as a result of the low driving fields. The magnetic nanorods have improved storage capacity in comparison to conventional components which leads to an increase in demand in the information and communication industry [4]. So, by reducing the size, we saw an increases in the production of flexible components. ...
... First, 1 mM AOT solved in 10 mL ethylene glycol and 4 mL of deionized water, then 30 min on magnetic stirrer to deformation. After this step, 1 mmol of (NH 4 (Figure 1), while FE-SEM images shows a set of rods that are parallel to each other. The diameter and lengths of these nanorod are approximately 50 nm and several hundred nanometers until the several micrometers, respectively. ...
Nanorods in nanotechnology called a specific type of morphology of nanoscale materials that their dimensions range is from 1 to 100 nm. Nanorods can be synthesized from metal or semi-conductive material with a surface to volume ratio of 3–5. One method of making nanorods is direct chemical method. Ligands compounds as a shape control agents cause growth the nanorods and create stretched and extended modes of them. In recent years, magnetic nanorods are one of the nanorods that have been raised in the field of nano medicine [Nath S, Kaittanis C, Ramachandran V, Dalal NS, Perez JM. Synthesis, magnetic characterization, and sensing applications of novel dextran-coated iron oxide nanorods. Chem Mater. 2009;21:1761–7.]. Superparamagnetic properties of magnetic nanorods causes to sensing be done with high accuracy. In addition, other applications of magnetic nanorods are in the field of separation and treatment [Hu B, Wang N, Han L, Chen ML, Wang JH. Magnetic nanohybrids loaded with bimetal core–shell–shell nanorods for bacteria capture, separation, and near-infrared photothermal treatment. Chemistry. 2015;21:6582–9.]. Therefore, in biomedical applications, the nanorods are used usually with biological molecules such as antibodies [Schrittwieser S, Pelaz B, Parak WJ, Lentijo-Mozo S, Soulantica K, Dieckhoff J, et al. Homogeneous protein analysis by magnetic core–shell nanorod probes. ACS Appl Mater Interfaces. 2016;8:8893–9.]. For this purpose, in the present work we will try to introduce magnetic nanorods and mention their different methods of synthesis and applications.
... In this work we present a numerical study of the self-assembly of a two-dimensional system of stiff magnetic rods, composed of single dipolar beads linked one by one through internal head-to-tail alignment. A similar system was used earlier in experiment [24] and simulations [25]. Our motivation to explore in more detail the two-dimensional (2D) situation is driven by the fact that many experiments involving assemblies of colloids are actually done at surfaces and/or thin films [26][27][28][29][30]. * jorgecapuan@fisica.ufc.br ...
... We also study the connectivity properties of the present system. The percolation behavior is of great relevance in highly connected materials due to the possibility of enhancing the electrical and thermal conductivity [24,33]. In general, percolation in polymers plays a fundamental role in properties related to conductivity, because in many cases percolation can be made responsible for electrical switching properties. ...
... Common experimental values of μ * 2 at room temperature ranges in the interval 1 μ * 2 100. For example, in experiments using iron nanoparticles [24], it is found that the saturation magnetization M s (Fe) = 1700 kA/m and the radius of the particles is r ≈ 5 nm. In this case, we estimate μ * ≈ 4.4 at room temperature (T ≈ 293 K). ...
Molecular dynamics simulations are used to investigate the structural properties of a two-dimensional ensemble of magnetic rods, which are modeled as aligned single dipolar beads. The obtained self-assembled configurations can be characterized as (1) clusters, (2) percolated, and (3) ordered structures, and their structural properties are investigated in detail. By increasing the aspect ratio of the magnetic rods, we show that the percolation transition is suppressed due to the reduced mobility of the rods in two dimensions. Such a behavior is opposite to the one observed in three dimensions. A magnetic bulk phase is found with local ferromagnetic order and an unusual nonmonotonic behavior of the nematic order is observed.
