Micromagnetic Simulations of Fe and Ni Nanodot Arrays Surrounded by Magnetic or Non-Magnetic Matrices

Combining clusters of magnetic materials with a matrix of other magnetic materials is very interesting for basic research because new, possibly technologically applicable magnetic properties or magnetization reversal processes may be found. Here we report on different arrays combining iron and nickel, for example, by surrounding circular nanodots of one material with a matrix of the other or by combining iron and nickel nanodots in air. Micromagnetic simulations were performed using the OOMMF (Object Oriented MicroMagnetic Framework). Our results show that magnetization reversal processes are strongly influenced by neighboring nanodots and the magnetic matrix by which the nanodots are surrounded, respectively, which becomes macroscopically visible by several steps along the slopes of the hysteresis loops. Such material combinations allow for preparing quaternary memory systems, and are thus highly relevant for applications in data storage and processing.

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Micromagnetic Simulation of Round Ferromagnetic Nanodots with Varying Roughness and Symmetry

Condensed Matter ◽

10.3390/condmat6020019 ◽

2021 ◽

Vol 6 (2) ◽

pp. 19

Author(s):

Pia Steinmetz ◽

Andrea Ehrmann

Keyword(s):

Data Storage ◽

Magnetization Reversal ◽

Hysteresis Loops ◽

Basic Research ◽

Magnetic Data ◽

Field Orientation ◽

Thin Ring ◽

Production Technologies ◽

Magnetic States ◽

The Impact

Magnetic nanodots are of high interest for basic research due to their broad spectrum of possible magnetic states and magnetization reversal processes. Besides, they are of technological interest since they can be applied in magnetic data storage, especially if vortex states occur in closed dots or open rings. While producing such nanorings and nanodots from diverse magnetic materials by lithographic techniques is quite common nowadays, these production technologies are naturally prone to small deviations of the borders of these nanoparticles. Here we investigate the influence of well-defined angular-dependent roughness of the edges, created by building the nanoparticles from small cubes, on the resulting hysteresis loops and magnetization reversal processes in five different round nanodots with varying open areas, from a thin ring to a closed nanodot. By varying the orientation of the external magnetic field, the impact of the angle-dependent roughness can be estimated. Especially for the thinnest ring, significant dependence of the transverse magnetization component on the field orientation can be found.

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Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas

Nanomaterials ◽

10.3390/nano11030800 ◽

2021 ◽

Vol 11 (3) ◽

pp. 800

Author(s):

Joscha Detzmeier ◽

Kevin Königer ◽

Tomasz Blachowicz ◽

Andrea Ehrmann

Keyword(s):

Magnetization Reversal ◽

Thermal Effects ◽

Hysteresis Loops ◽

Ferromagnetic Nanoparticles ◽

Zero Temperature ◽

Small Deviations ◽

Micromagnetic Simulations ◽

Random Anisotropy ◽

Ferromagnetic Nanostructures ◽

Biased Samples

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles.

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Magnetization Reversal Process and Magnetostatic Interactions in Fe56Co44/SiO2/Fe3O4 Core/Shell Ferromagnetic Nanowires with Non-Magnetic Interlayer

Nanomaterials ◽

10.3390/nano11092282 ◽

2021 ◽

Vol 11 (9) ◽

pp. 2282

Author(s):

Javier García ◽

Alejandro M. Manterola ◽

Miguel Méndez ◽

Jose Angel Fernández-Roldán ◽

Víctor Vega ◽

...

Keyword(s):

Data Storage ◽

Magnetization Reversal ◽

Domain Walls ◽

Magnetic Domain ◽

Hysteresis Loops ◽

Magnetic Data ◽

Core Shell ◽

The Core ◽

Shell Nanostructures ◽

Magnetostatic Interactions

Nowadays, numerous works regarding nanowires or nanotubes are being published, studying different combinations of materials or geometries with single or multiple layers. However, works, where both nanotube and nanowires are forming complex structures, are scarcer due to the underlying difficulties that their fabrication and characterization entail. Among the specific applications for these nanostructures that can be used in sensing or high-density magnetic data storage devices, there are the fields of photonics or spintronics. To achieve further improvements in these research fields, a complete understanding of the magnetic properties exhibited by these nanostructures is needed, including their magnetization reversal processes and control of the magnetic domain walls. In order to gain a deeper insight into this topic, complex systems are being fabricated by altering their dimensions or composition. In this work, a successful process flow for the additive fabrication of core/shell nanowires arrays is developed. The core/shell nanostructures fabricated here consist of a magnetic nanowire nucleus (Fe56Co44), grown by electrodeposition and coated by a non-magnetic SiO2 layer coaxially surrounded by a magnetic Fe3O4 nanotubular coating both fabricated by means of the Atomic Layer Deposition (ALD) technique. Moreover, the magnetization reversal processes of these coaxial nanostructures and the magnetostatic interactions between the two magnetic components are investigated by means of standard magnetometry and First Order Reversal Curve methodology. From this study, a two-step magnetization reversal of the core/shell bimagnetic nanostructure is inferred, which is also corroborated by the hysteresis loops of individual core/shell nanostructures measured by Kerr effect-based magnetometer.

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Micromagnetic Simulation of Vortex Development in Magnetic Bi-Material Bow-Tie Structures

Condensed Matter ◽

10.3390/condmat5010005 ◽

2020 ◽

Vol 5 (1) ◽

pp. 5 ◽

Cited By ~ 3

Author(s):

Devika Sudsom ◽

Irén Juhász Junger ◽

Christoph Döpke ◽

Tomasz Blachowicz ◽

Lothar Hahn ◽

...

Keyword(s):

Data Storage ◽

Vortex Formation ◽

Basic Research ◽

Micromagnetic Simulation ◽

Magnetic Vortex ◽

Magnetic Memory ◽

Thick Sample ◽

Field Orientation ◽

Micromagnetic Simulations ◽

Bow Tie

Magnetic vortex structures are of high technological relevance due to their possible application in magnetic memory. Moreover, investigating magnetization reversal via vortex formation is an important topic in basic research. Typically, such vortices are only investigated in homogeneous magnetic materials of diverse shapes. Here, we report for the first time on micromagnetic simulation of vortex formation in magnetic bow-tie nanostructures, comprising alternating parts from iron and permalloy, investigated for two different thicknesses and under different angles of the external magnetic field. While no vortex was found in pure permalloy square, nanoparticles of the dimensions investigated in this study and in case of iron only a relatively thick sample allowed for vortex formation, different numbers of vortices and antivortices were found in the bow-tie structures prepared from both materials, depending on the angular field orientation and the sample thickness. By stabilizing more than one vortex in a confined nanostructure, it is possible to store more than one bit of information in it. Our micromagnetic simulations reveal that such bi-material structures are highly relevant not only for basic research, but also for data storage applications.

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Micromagnetic study of the vortex state in sub-micron iron discs

EPJ Web of Conferences ◽

10.1051/epjconf/202023305002 ◽

2020 ◽

Vol 233 ◽

pp. 05002

Author(s):

Ludgero Peixoto ◽

C. Sousa ◽

D. Navas ◽

J.P. Araújo

Keyword(s):

Data Storage ◽

Magnetic Nanostructures ◽

Hysteresis Loops ◽

Vortex State ◽

Magnetic Behaviour ◽

Micromagnetic Simulations ◽

Research Fields ◽

Plane Anisotropy ◽

The Difference ◽

The Ideal

Magnetic nanostructures have been widely studied due to its poten¬tial applicability into several research fields such as data storage, sensing and biomedical applications. In this work, micromagnetic simulations (mumax3) of sub-micron iron discs are performed for different normalized inter-dot distance (distance/diameter), to better understand the magnetic behaviour of these nanos-tructures. Two sets of samples were studied: ideal circular discs and disc-shaped nanostructures (based on images of real samples). By analyzing the nucleation and annihilation fields and the magnetic susceptibility, it was found that the (ideal) discs could be considered as isolated for inter-dot distances greater than twice the raidus of the disc (2R). The difference in the shape of the disc-shaped nanostructures resulted in an in-plane anisotropy, noticeable on the hysteresis loops for different directions.

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Magnetization Reversal in Concave Iron Nano-Superellipses

Condensed Matter ◽

10.3390/condmat6020017 ◽

2021 ◽

Vol 6 (2) ◽

pp. 17

Author(s):

Emre Öncü ◽

Andrea Ehrmann

Keyword(s):

Magnetic Field ◽

External Magnetic Field ◽

Magnetization Reversal ◽

Hysteresis Loops ◽

Strong Impact ◽

Research Groups ◽

Micromagnetic Simulations ◽

Magnetic Nanodots ◽

Reversal Process ◽

Magnetization Reversal Process

Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid. Due to the strong impact of shape anisotropy in nanostructures, the magnetization-reversal process including coercive and reversibility fields can be expected to be different in concave or convex superellipses than that in common squares. Here, we present angle-dependent micromagnetic simulations on magnetic nanodots with the shape of concave superellipses. While magnetization reversal occurs via meander states, horseshoe states or the 180° rotation of magnetization for the perfect square, depending on the angle of the external magnetic field, more complicated states occur for superellipses with strong concaveness. Even apparently asymmetric hysteresis loops can be found along the hard magnetization directions, which can be attributed to measuring minor loops since the reversibility fields become much larger than the coercive fields.

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Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of bi-Segmented FeNi Nanowires

10.20944/preprints201807.0268.v1 ◽

2018 ◽

Author(s):

Miguel Méndez ◽

Víctor Vega ◽

Silvia González ◽

Rafael Caballero-Flores ◽

Javier García ◽

...

Keyword(s):

Data Storage ◽

Magnetization Reversal ◽

Magnetic Nanostructures ◽

Magnetic Behavior ◽

Magnetic Data ◽

Micromagnetic Simulations ◽

Precise Control ◽

Different Types ◽

Magnetic Decoupling ◽

Different Diameters

Controlling functional properties of matter and combine them for engineering a functional device is nowadays a common direction of scientific community. For instance, heterogeneous magnetic nanostructures can make use of different types of geometrical and compositional modulations to achieve the control of the magnetization reversal along with the nano-entities and thus enabling the fabrication of spintronic, magnetic data storage and sensing devices, among others. In this work, diameter modulated FeNi nanowires are fabricated paying special effort to obtain sharp transition regions between two segments of different diameters (from about 450 nm to 120 nm), enabling precise control over the magnetic behavior of the sample. Micromagnetic simulations performed on single bi-segmented nanowires predict a double step magnetization reversal where the wide segment magnetization switches near 200 Oe through a vortex domain wall, while at 500 Oe the magnetization of the narrow one is reversed through a corkscrew like mechanism. Finally, these results are confirmed with magneto-optic Kerr effect measurements at the transition of isolated bi-segmented nanowires. Furthermore, macroscopic vibrating sample magnetometry is used to demonstrate that the magnetic decoupling of nanowire segments is the main phenomenon occurring over the entire fabricated nanowires.

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Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of Bi-Segmented FeNi Nanowires

Nanomaterials ◽

10.3390/nano8080595 ◽

2018 ◽

Vol 8 (8) ◽

pp. 595 ◽

Cited By ~ 7

Author(s):

Miguel Méndez ◽

Víctor Vega ◽

Silvia González ◽

Rafael Caballero-Flores ◽

Javier García ◽

...

Keyword(s):

Data Storage ◽

Magnetization Reversal ◽

Magnetic Nanostructures ◽

Magnetic Behavior ◽

Magnetic Data ◽

Micromagnetic Simulations ◽

Precise Control ◽

Different Types ◽

Magnetic Decoupling ◽

Different Diameters

Controlling functional properties of matter and combining them for engineering a functional device is, nowadays, a common direction of the scientific community. For instance, heterogeneous magnetic nanostructures can make use of different types of geometrical and compositional modulations to achieve the control of the magnetization reversal along with the nano-entities and, thus, enable the fabrication of spintronic, magnetic data storage, and sensing devices, among others. In this work, diameter-modulated FeNi nanowires are fabricated paying special effort to obtain sharp transition regions between two segments of different diameters (from about 450 nm to 120 nm), enabling precise control over the magnetic behavior of the sample. Micromagnetic simulations performed on single bi-segmented nanowires predict a double step magnetization reversal where the wide segment magnetization switches near 16 kA/m through a vortex domain wall, while at 40 kA/m the magnetization of the narrow segment is reversed through a corkscrew-like mechanism. Finally, these results are confirmed with magneto-optic Kerr effect measurements at the transition of isolated bi-segmented nanowires. Furthermore, macroscopic vibrating sample magnetometry is used to demonstrate that the magnetic decoupling of nanowire segments is the main phenomenon occurring over the entire fabricated nanowires.

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Narrow Segment Driven Multistep Magnetization Reversal Process in Sharp Diameter Modulated Fe67Co33 Nanowires

Nanomaterials ◽

10.3390/nano11113077 ◽

2021 ◽

Vol 11 (11) ◽

pp. 3077

Author(s):

Javier García ◽

Jose A. Fernández-Roldán ◽

Roque González ◽

Miguel Méndez ◽

Cristina Bran ◽

...

Keyword(s):

Data Storage ◽

Magnetization Reversal ◽

Domain Walls ◽

Nanowire Array ◽

Magnetic Hysteresis ◽

Magnetic Domain ◽

Hysteresis Loops ◽

Magnetic Behavior ◽

Magnetic Nanomaterials ◽

Magnetic Nanowires

Magnetic nanomaterials are of great interest due to their potential use in data storage, biotechnology, or spintronic based devices, among others. The control of magnetism at such scale entails complexing the nanostructures by tuning their composition, shape, sizes, or even several of these properties at the same time, in order to search for new phenomena or optimize their performance. An interesting pathway to affect the dynamics of the magnetization reversal in ferromagnetic nanostructures is to introduce geometrical modulations to act as nucleation or pinning centers for the magnetic domain walls. Considering the case of 3D magnetic nanowires, the modulation of the diameter across their length can produce such effect as long as the segment diameter transition is sharp enough. In this work, diameter modulated Fe67Co33 ferromagnetic nanowires have been grown into the prepatterned diameter modulated nanopores of anodized Al2O3 membranes. Their morphological and compositional characterization was carried out by electron-based microscopy, while their magnetic behavior has been measured on both the nanowire array as well as for individual bisegmented nanowires after being released from the alumina template. The magnetic hysteresis loops, together with the evaluation of First Order Reversal Curve diagrams, point out that the magnetization reversal of the bisegmented FeCo nanowires is carried out in two steps. These two stages are interpreted by micromagnetic modeling, where a shell of the wide segment reverses its magnetization first, followed by the reversal of its core together with the narrow segment of the nanowire at once.

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Discovering the Other: Study Abroad as Fieldwork

Frontiers: The Interdisciplinary Journal of Study Abroad ◽

10.36366/frontiers.v2i1.32 ◽

1996 ◽

Vol 2 (1) ◽

pp. 111-122

Author(s):

Joseph R. Stimpfl

Keyword(s):

Study Abroad ◽

Cultural Anthropology ◽

Participant Observation ◽

Basic Research ◽

Cultural Adjustment ◽

The Other ◽

Cultural Immersion ◽

Cultural Learning ◽

Fieldwork Experience ◽

Different Cultures

The literature annotated here is from a subset of literature in cultural anthropology that deals with ethnographic fieldwork: the basic research exercise of cultural immersion. This bibliography is meant to offer a representative sample of literature in anthropology that deals with the fieldwork experiences of researchers. Cultural anthropology is devoted to the concept of “discovering the other.” Its method of inquiry is often referred to as participant/observation: the researcher lives the culture while observing it. Since so much of the fieldwork experience deals with personal adjustments to living in different cultures, the literature is charged with the problems of adjustment and understanding so common to study abroad experiences. This literature is particularly relevant to those interested in cross-cultural learning and issues in cultural adjustment.

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