Numerical simulation of magnetic nanoparticles

We solved the Landau-Lifshitz equations numerically to examine the time development of a system of magnetic particles. Constant or periodical external magnetic field has been applied. First, the system has been studied without dissipation. Local energy excitations (breathers) and chaotic transients have been found. The behaviour of the system and the final configurations can strongly depend on the initial conditions, and the strength of the external field at an earlier time. We observed some sudden switching between two remarkably different states. Series of bifurcations have been found. When a weak Gilbert-damping has been taken into account, interesting behaviour has been found even in the case of one particle as well: bifurcation series and period multiplication leading to chaos. For a system of antiferromagnetically coupled particles, highly nontrivial hysteresis loops have been produced. The dynamics of the magnetization reversal has been investigated and the characteristic time-scale of the reversal has been estimated. For more particles, the energy spectrum and the magnetization of the system exhibits fractal characteristics for increasing system size. Finally, energy have been pumped into the system in addition to the dissipation. For constant field, complicated phase diagrams have been produced. For microwave field, it has been found that the chaotic behaviour crucially depends on the parity of the number of the particles

Switching dynamics of doped CoFeB trilayers and a comparison to the quasistatic approximation

The investigation of the switching times of the magnetization reversal of two interacting CoFeB nanomagnets, with dimensions small enough to maintain a single-domain structure, has been carried out. A quasistatic approximation is shown to give valid results and to compare well to the damped dynamical solutions of the Landau-Lifshitz-Gilbert equations. The characteristics of the switching are shown in the associated hysteresis loops and we build a complete phase diagram of the various parallel, antiparallel, and scissoring states of the magnetization in terms of the coupling energy between the nanomagnets, magnetic anisotropy, and the interaction with an applied magnetic field. The phase diagram summarizes the different kinds of hysteresis associated with the magnetization reversal phenomena. The switching fields and times are estimated and the vulnerabilities of the magnetic phases to thermally induced magnetic field variations are examined. The stability of the phases is a fine balance between intrinsic and extrinsic magnetism and we examine its precarious nature. Our work identifies the structures that have the most robust magnetization states and hence a design ethic for creating nanomagnetic heterostructures with outstanding magnetoresistance properties based upon the two magnetic elements

Designing magnetic superlattices that are composed of single domain nanomagnets

Background: The complex nature of the magnetic interactions between any number of nanosized elements of a magnetic superlattice can be described by the generic behavior that is presented here. The hysteresis characteristics of interacting elliptical nanomagnets are described by a quasi-static method that identifies the critical boundaries between magnetic phases. A full dynamical analysis is conducted in complement to this and the deviations from the quasi-static analysis are highlighted. Each phase is defined by the configuration of the magnetic moments of the chain of single domain nanomagnets and correspondingly the existence of parallel, anti-parallel and canting average magnetization states. Results: We give examples of the phase diagrams in terms of anisotropy and coupling strength for two, three and four magnetic layers. Each phase diagrams character is defined by the shape of the magnetic hysteresis profile for a system in an applied magnetic field. We present the analytical solutions that enable one to define the “phase” boundaries between the emergence of spin-flop, anti-parallel and parallel configurations. The shape of the hysteresis profile is a function of the coupling strength between the nanomagnets and examples are given of how it dictates a systems magnetic response. Many different paths between metastable states can exist and this can lead to instabilities and fluctuations in the magnetization. Conclusion: With these phase diagrams one can find the most stable magnetic configurations against perturbations so as to create magnetic devices. On the other hand, one may require a magnetic system that can easily be switched between phases, and so one can use the information herein to design superlattices of the required shape and character by choosing parameters close to the phase boundaries. This work will be useful when designing future spintronic devices, especially those manipulating the properties of CoFeB compounds

Numerical simulation of antiferromagnetically coupled nanomagnets

We study the dynamical behaviour of a system that consists of three identical elongated nanomagnets. The magnets are coupled antiferromagnetically and subjected to periodically changing external magnetic field. The numerical simulation of the system reveals the qualitatively different kinds of hysteresis loops

Indications of possible chaos in arrays of single-domain nanomagnets.

We study the dynamical behaviour of a system that consists of one or two elongated nanomagnets. The magnets are coupled antiferromagnetically and subjected to periodically changing external magnetic field. The numerical simulation of the system reveals the possibility of chaotic behaviour

Performanse tri populacije mlađi smuđa (sander lucioperca) iz Mađarske u intenzivnom uzgoju

Zahvaljujući blagom ukusu i niskom sadržaju masti uz poželjan masno-kiselinski sastav smuđ (Sander lucioperca) je cenjen među potrošačima i uz pad izlova i povećanje potražnje dobija sve veću pažnju među uzgajivačima. S obzirom da su osnovni izvori matica smuđa iz ekstenzivnog uzgoja ili divljeg porekla, informacija o podobnosti mlađi pomenutog porekla sa svrhom intenzivnog uzgoja je od izuzetnog značaja. S tom svrhom, naša namera bila je da ovom studijom ocenimo performanse dve grupe mlađi poreklom od matica iz ekstenzivnog uzgoja i jedne grupe mlađi poreklom od divljih matica iz najveće vodene mase u državi, reke Dunav, kao i da ocenimo stepen zadržavanja NMT Alpha vidljivih oznaka u obraz riba. Iako bez statistički značajne razlike, mlađ poreklom iz ekstenzivnog uzgoja ispoljila je brži rast. Ovakav rezultat nagoveštava obimnu selekciju među maticama iz jezerskog uzgoja, posebno uzimajući u obzir stres rukovanja i suboptimalne uslove kvaliteta vode što sezonski karakteriše jezerski uzgoj. Kakogod, treba nagovestiti da je u svakoj grupi zabeležena određena količina iznurenih individua. Konačno, primanje NMT Alpha vidljivih oznaka je bilo visoko u sve tri grupe i bez statistički značajnih razlika

Additive Manufacturing of 17-4PH Alloy: Tailoring the Printing Orientation for Enhanced Aerospace Application Performance

Additive manufacturing (AM) is one of the fastest-growing markets of our time. During its journey in the past 30 years, its key to success has been that it can easily produce extremely complex shapes and is not limited by tooling problems when a change in geometry is desired. This flexibility leads to possible solutions for creating lightweight structural elements while keeping the mechanical properties at a stable reserve factor value. In the aerospace industry, several kinds of structural elements for fuselage and wing parts are made from different kinds of steel alloys, such as 17-4PH stainless steel, which are usually milled from a block material made using conventional processing (CP) methods. However, these approaches are limited when a relatively small element must withstand greater forces that can occur during flight. AM can bridge this problem with a new perspective, mainly using thin walls and complex shapes while maintaining the ideal sizes. The downside of the elements made using AM is that the quality of the final product is highly dependent on the build/printing orientation, an issue extensively studied and addressed by researchers in the field. During flight, some components may experience forces that predominantly act in a single direction. With this in mind, we created samples with the desired orientation to maximize material properties in a specific direction. The goal of this study was to demonstrate that an additively manufactured part, produced using laser powder bed fusion (LPBF), with a desired build orientation has exceptional properties compared to parts produced via conventional methods. To assess the impact of the build orientation on the LPBF parts’ properties, one-dimensional tensile and dynamic fracture toughness tests were deployed

Crustal Architecture of the Inverted Central Lapland Rift Along the HUKKA 2007 Profile

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