312 research outputs found
Magnetization pinning in modulated nanowires: from topological protection to the "corkscrew" mechanism
Diameter-modulated nanowires offer an important paradigm to design the
magnetization response of 3D magnetic nanostructures by engineering the domain
wall pinning. With the aim to understand its nature and to control the process,
we analyze the magnetization response in FeCo modulated polycrystalline
two-segment nanowires varying the minor diameter. Our modelling indicates a
very complex behavior with a strong dependence on the disorder distribution and
an important role of topologically non-trivial magnetization structures. We
demonstrate that modulated nanowires with a small diameter difference are
characterized by an increased coercive field in comparison to the straight ones
which is explained by a formation of topologically protected walls formed by
two 3D skyrmions with opposite chiralities. For a large diameter difference we
report the occurrence of a novel pinning type called here the "corkscrew": the
magnetization of the large diameter segment forms a skyrmion tube with a core
position in a helical modulation along the nanowire. This structure is pinned
at the constriction and in order to penetrate the narrow segments the
vortex/skyrmion core size should be reduced
Investigation of the thermophysical properties of high-melting materials with the aid of a complex of instruments
The evaporation rate, vapor pressure, heats of evaporation reaction (sublimation, dissociation), enthalpy, electrical resistance, heat capacity, emissivity, and heat conductivity of various carbides, borides, sulfides, nitrides, selenides, and phosphides were investigated. A set of high temperature high vacuum devices, calorimeters (designed for operation at 400 to 1300 K and from 1200 K), and mass spectrometers, most of which were specially developed for these studies, is described
Micromagnetic modelling of magnetic domain walls and domains in cylindrical nanowires
Magnetic cylindrical nanowires are very fascinating objects where the curved
geometry allows many novel magnetic effects and a variety of non-trivial
magnetic structures. Micromagnetic modelling plays an important role in
revealing the magnetization distribution in magnetic nanowires, often not
accessible by imaging methods with sufficient details. Here we review the
magnetic properties of the shape anisotropy-dominated nanowires and the
nanowires with competing shape and magnetocrystalline anisotropies, as revealed
by micromagnetic modelling. We discuss the variety of magnetic walls and
magnetic domains reported by micromagnetic simulations in cylindrical
nanowires. The most known domain walls types are the transverse and vortex
(Bloch point) domain walls and the transition between them is materials and
nanowire diameter dependent. Importantly, the field or current-driven domain
walls in cylindrical nanowires can achieve very high velocities. In recent
simulations of nanowires with larger diameter the skyrmion tubes are also
reported. In nanowires with large saturation magnetization the core of these
tubes may form a helicoidal ('corkscrew') structure. The topology of the
skyrmion tubes play an important role in the pinning mechanism, discussed here
on the example of FeCo modulated nanowires. Other discussed examples include
the influence of antinotches ('bamboo' nanowires) on the remanent magnetization
configurations for hcp Co and FeCo nanowires and Co-Ni multisegmented
nanowires.Comment: 24 pages, 17 figures, 1 tabl
Effect of Nb cationic substitution on the microstructure and Raman spectra of SrBi2(Ta,Nb)2O9 thin films
Micro-Raman spectroscopy and x-ray diffraction have been used to explore the
lattice dynamics of Nb-substituted SrBi2(TaxNb1-x)2O9 (SBTN) thin crystalline
films annealed at low temperature, 700oC. The substitution of Nb at Ta-site
leads to the decrease in the SBT lattice parameters, as confirmed by x-ray
diffraction data entire the concentration range of Nb varying from 0 to 50 wt.
%. The relative intensity of the (115), (006) and (200) X-ray diffraction peaks
increases with the increase of the Nb content. We observed nonmonotonic shift
of the Raman band maximum from 810 cm-1 (for pure SBT) to 830 cm-1 (for SBTN
with 20 % of Nb) and then back to 810 cm-1 with increasing Nb content from 40
to 50 wt. %. We assume that these changes are conditioned by the
ferrodistortion occurring in ferroic perovskites, namely by the tilting
distortion of (Ta,Nb)O6 octahedra at 20-40 wt. % of Nb. The octahedra tilting
can change the coordination environment of the A-cite cation, as well as it
lowers the SBTN symmetry below the cubic symmetry. The tilted state at 20-40
wt. % of Nb can explain the nonmonotonic changes of the perovskite phase
fraction and remanent polarization with increasing Nb content from 0 to 50
wt.%, in particular their initial increase with Nb content increase up to 20
wt. % followed by a decrease at 30 wt. % of Nb, then increase at 40 wt.% and
further decrease for 40 - 50 wt.% of Nb. Hence, the substitution by Nb of
Ta-site in SBT has a pronounced impact on the O-Ta-O stretching modes by
shifting and splitting the mode frequency at (810 - 830) cm-1; however, it does
not influence the low frequency Raman modes of SBTN.Landau-Devonshire approach
is used to explain the experimentally observed nonmonotonic dependence of the
ferroelectric perovskite phase fraction and remanent polarization on Nb content
in SBTN films.Comment: 24 pages, 12 figure
The 2020 magnetism roadmap
Following the success and relevance of the 2014 and 2017 Magnetism Roadmap articles, this 2020 Magnetism Roadmap edition takes yet another timely look at newly relevant and highly active areas in magnetism research. The overall layout of this article is unchanged, given that it has proved the most appropriate way to convey the most relevant aspects of today's magnetism research in a wide variety of sub-fields to a broad readership. A different group of experts has again been selected for this article, representing both the breadth of new research areas, and the desire to incorporate different voices and viewpoints. The latter is especially relevant for thistype of article, in which one's field of expertise has to be accommodated on two printed pages only, so that personal selection preferences are naturally rather more visible than in other types of articles. Most importantly, the very relevant advances in the field of magnetism research in recent years make the publication of yet another Magnetism Roadmap a very sensible and timely endeavour, allowing its authors and readers to take another broad-based, but concise look at the most significant developments in magnetism, their precise status, their challenges, and their anticipated future developments. While many of the contributions in this 2020 Magnetism Roadmap edition have significant associations with different aspects of magnetism, the general layout can nonetheless be classified in terms of three main themes: (i) phenomena, (ii) materials and characterization, and (iii) applications and devices. While these categories are unsurprisingly rather similar to the 2017 Roadmap, the order is different, in that the 2020 Roadmap considers phenomena first, even if their occurrences are naturally very difficult to separate from the materials exhibiting such phenomena. Nonetheless, the specifically selected topics seemed to be best displayed in the order presented here, in particular, because many of the phenomena or geometries discussed in (i) can be found or designed into a large variety of materials, so that the progression of the article embarks from more general concepts to more specific classes of materials in the selected order. Given that applications and devices are based on both phenomena and materials, it seemed most appropriate to close the article with the application and devices section (iii) once again. The 2020 Magnetism Roadmap article contains 14 sections, all of which were written by individual authors and experts, specifically addressing a subject in terms of its status, advances, challenges and perspectives in just two pages. Evidently, this two-page format limits the depth to which each subject can be described. Nonetheless, the most relevant and key aspects of each field are touched upon, which enables the Roadmap as whole to give its readership an initial overview of and outlook into a wide variety of topics and fields in a fairly condensed format. Correspondingly, the Roadmap pursues the goal of giving each reader a brief reference frame of relevant and current topics in modern applied magnetism research, even if not all sub-fields can be represented here. The first block of this 2020 Magnetism Roadmap, which is focussed on (i) phenomena, contains five contributions, which address the areas of interfacial Dzyaloshinskii-Moriya interactions, and two-dimensional and curvilinear magnetism, as well as spin-orbit torque phenomena and all optical magnetization reversal.
All of these contributions describe cutting edge aspects of rather fundamental physical processes and properties, associated with new and improved magnetic materials' properties, together with potential developments in terms of future devices and technology. As such, they form part of a widening magnetism 'phenomena reservoir' for utilization in applied magnetism and related device technology. The final block (iii) of this article focuses on such applications and device-related fields in four contributions relating to currently active areas of research, which are of course utilizing magnetic phenomena to enable specific functions. These contributions highlight the role of magnetism or spintronics in the field of neuromorphic and reservoir computing, terahertz technology, and domain wall-based logic. One aspect common to all of these application-related contributions is that they are not yet being utilized in commercially available technology; it is currently still an open question, whether or not such technological applications will be magnetism-based at all in the future, or if other types of materials and phenomena will yet outperform magnetism. This last point is actually a very good indication of the vibrancy of applied magnetism research today, given that it demonstrates that magnetism research is able to venture into novel application fields, based upon its portfolio of phenomena, effects and materials. This materials portfolio in particular defines the central block (ii) of this article, with its five contributions interconnecting phenomena with devices, for which materials and the characterization of their properties is the decisive discriminator between purely academically interesting aspects and the true viability of real-life devices, because only available materials and their associated fabrication and characterization methods permit reliable technological implementation. These five contributions specifically address magnetic films and multiferroic heterostructures for the purpose of spin electronic utilization, multi-scale materials modelling, and magnetic materials design based upon machine-learning, as well as materials characterization via polarized neutron measurements. As such, these contributions illustrate the balanced relevance of research into experimental and modelling magnetic materials, as well the importance of sophisticated characterization methods that allow for an ever-more refined understanding of materials. As a combined and integrated article, this 2020 Magnetism Roadmap is intended to be a reference point for current, novel and emerging research directions in modern magnetism, just as its 2014 and 2017 predecessors have been in previous years
In-vivo Studies of Ultrasound-activated Drug-loaded Porous Silicon Nanoparticles for Cancer Therapy Application
It is investigated the therapeutic efficacy of combined action of ultrasound and porous silicon nanoparticles loaded with anticancer drug doxorubicin by using an experimental cancer model of lung Lewis carcinoma in vivo. Time dependences of growth of the primary tumor with introduced nanoparticles and without them, as well as the life span of mice after exposure to therapeutic ultrasound with intensity of 1W/cm2 and frequency of 1 MHz were studied. The obtained results show the effectiveness of inhibiting the growth of primary tumor site, as well as slowing the process of metastasis, in the case of combined action of ultrasound and drug-loaded porous silicon nanoparticles that indicates the prospect of latter as sonosensitizers and nanocontainers for the delivery and controlled release of drugs in sonodynamic therapy of malignant tumors.
Keywords: silicon nanoparticles, nanocontainers, medical ultrasound, sonodynamic therapy, sonosensitizer
Pressure effect on the in-plane magnetic penetration depth in YBa_2Cu_4O_8
We report a study of the pressure effect (PE) on the in-plane magnetic field
penetration depth lambda_{ab} in YBa_2Cu_4O_8 by means of Meissner fraction
measurements. A pronounced PE on lambda_{ab}^{-2}(0) was observed with a
maximum relative shift of \Delta\lambda^{-2}_{ab}/\lambda^{-2}_{ab}= 44(3)% at
a pressure of 10.2 kbar. It arises from the pressure dependence of the
effective in-plane charge carrier mass and pressure induced charge carrier
transfer from the CuO chains to the superconducting CuO_2 planes. The present
results imply that the charge carriers in YBa_2Cu_4O_8 are coupled to the
lattice.Comment: 4pages 3 figure
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