Writing and Deleting Single Magnetic Skyrmions Romming, Niklas; Hanneken, Christian; Menzel, Matthias ...
Science (American Association for the Advancement of Science),
08/2013, Letnik:
341, Številka:
6146
Journal Article
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Topologically nontrivial spin textures have recently been investigated for spintronic applications. Here, we report on an ultrathin magnetic film in which individual skyrmions can be written and ...deleted in a controlled fashion with local spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection. The creation and annihilation of individual magnetic skyrmions demonstrates the potential for topological charge in future information-storage concepts.
LaFeOsub.3 thin films were successfully epitaxially grown on single-crystalline SrTiOsub.3 substrates by the one-step hydrothermal method at a temperature of 320 °C in a 10 mol/L KOH aqueous solution ...using La(NOsub.3)sub.3 and Fe(NOsub.3)sub.3 as the raw materials. The growth of the films was consistent with the island growth mode. Scanning electronic microscopy, elemental mapping, and atomic force microscopy demonstrate that the LaFeOsub.3 thin films cover the SrTiOsub.3 substrate thoroughly. The film subjected to hydrothermal treatment for 4 h exhibits a relatively smooth surface, with an average surface roughness of 10.1 nm. X-ray diffraction in conventional Bragg–Brentano mode shows that the LaFeOsub.3 thin films show the same out-of-plane orientation as that of the substrate (i.e., (001)sub.LaFeO3||(001)sub.SrTiO3). The in-plane orientation of the films was analyzed by φ-scanning, revealing that the orientational relationship is 001sub.LaFeO3||001sub.SrTiO3. The ω-rocking curve indicates that the prepared LaFeOsub.3 films are of high quality with no significant mosaic defects.
Cubic structured manganese ferrite nanoparticles were synthesized by a thermal treatment method followed by calcination at various temperatures from 723 to 873K. In this investigation, we used ...polyvinyl pyrrolidon (PVP) as a capping agent to control the agglomeration of the nanoparticles. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle sizes of manganese ferrite nanoparticles were determined by TEM, which increased with the calcination temperature from 12 to 22nm and they had good agreement with XRD results. Fourier transform infrared spectroscopy confirmed the presence of metal oxide bands at all temperatures and the absence of organic bands at 873K. Magnetic properties were demonstrated by a vibrating sample magnetometer, which showed a super-paramagnetic behavior for all samples and also saturation magnetization (Ms) increases from 3.06 to 15.78emu/g by increasing the calcination temperature. The magnetic properties were also confirmed by the use of electron paramagnetic resonance spectroscopy, which revealed the existence of unpaired electrons and also measured peak-to-peak line width, resonant magnetic field and the g-factor.
► Cubic structured manganese ferrite nano particles were synthesized by a thermal treatment method. ► Polyvinylpyrrolidon (PVP) has been used as a capping agent to control the agglomeration of the nanoparticles. ► The average particle sizes of manganese ferrite nano particles were determined by TEM.
Multiprincipal‐element alloys (MPEAs), including high‐entropy alloys, are a new class of materials whose thermodynamical properties are mainly driven by configuration entropy, rather than enthalpy in ...the traditional alloys, especially at high temperatures. Herein, the design of a novel soft‐magnetic nonequiatomic, quaternary MPEA is described, via tuning its chemical composition to deliberately manipulate its microstructure, such that it contains ultrafine ferromagnetic body‐centered‐cubic (BCC) coherent nanoprecipitates (3–7 nm) uniformly distributed in a B2‐phase matrix. The new alloy Al1.5Co4Fe2Cr exhibits high saturation magnetization (MS = 135.3 emu g‐1), low coercivity (HC = 127.3 A m‐1), high Curie temperature (TC = 1061 K), and high electrical resistivity (ρ = 244 μΩ cm), promising for soft magnets. More importantly, these prominent soft‐magnetic properties are observed to be retained even after the alloy is thermally exposed at 873 K for 555 h, apparently attributable to the excellent stability of the coherent microstructure. The versatility of the magnetic properties of this new alloy is discussed in light of the microstructural change induced by tuning the chemical composition, and the enhanced performance of the alloy is compared directly with that of the traditional soft‐magnetic alloys. The perspective is also addressed to design high‐performance soft‐magnetic alloys for high‐temperature applications.
A novel Al1.5Co4Fe2Cr multiprincipal element alloy with ultrafine ferromagnetic body‐centered‐cubic (BCC) coherent nanoprecipitates in a B2 matrix is developed via tuning the chemical composition to manipulate the microstructure. It exhibits a prominent soft‐magnetic property, high Curie temperature, and electrical resistivity, apparently attributable to the excellent stability of the coherent microstructure. The current approach offers a new way to design high‐performance soft‐magnetic alloys for high‐temperature applications.
Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. ...kappa-(BEDT-TTF).sub.2Cu.sub.2(CN).sub.3 is considered the prime candidate for this elusive quantum spin liquid state, but its ground-state properties remain puzzling. We present a multifrequency electron spin resonance (ESR) study down to millikelvin temperatures, revealing a rapid drop of the spin susceptibility at 6 kelvin. This opening of a spin gap, accompanied by structural modifications, is consistent with the formation of a valence bond solid ground state. We identify an impurity contribution to the ESR response that becomes dominant when the intrinsic spins form singlets. Probing the electrons directly manifests the pivotal role of defects for the low-energy properties of quantum spin systems without magnetic order.
Axisymmetric magnetic string-like objects of nanometre sizes (chiral
vortices
or
skyrmions
) have been predicted to exist in a large group of noncentrosymmetric crystals more than two decades ago. ...Recently, these magnetic textures have been directly observed in nanolayers of cubic helimagnets and monolayers of magnetic metals. We develop a micromagnetic theory of chiral skyrmions in thin magnetic layers for magnetic materials with intrinsic and induced chirality. Such particle-like and stable micromagnetic objects can exist in broad ranges of applied magnetic fields including zero field. Chiral skyrmions can be used as a new type of highly mobile nanoscale data carriers.
Based on the fact that tumor cells are more thermolabile and less oxygen resistant than normal cells, a novel minimally invasive tumor treatment modality, magnetic hyperthermia (MHT) is proposed. ...However, magnetic materials, which are necessities in MHT, are toxic to human tissue if they are excessively employed. Thus, magnetic materials with higher specific absorption rate (SAR) and intrinsic loss power (ILP) values becomes imperative to minimize their clinical application while mitigating damage to normal human tissues under identical treatment temperature conditions. In this study, the incorporation of soft magnetic MnFe2O4 into hard magnetic CoFe2O4 was introduced, leveraging the exchange coupling between these materials to enhance the magnetic saturation (Ms). Subsequently, we combined these magnetic nanomaterials with graphene oxide (GO) to establish an efficient heat conduction pathway, further augmenting the specific absorption rate (SAR) value of the resulting magnetic composites. Our findings reveal that the Mn0.5Co0.5Fe2O4-1%GO composite developed in this investigation boasts superior SAR values and intrinsic loss power (ILP) of 49.7 W/g and 5.90 nHm2/kg, respectively, when compared to other magnetic materials. The nanomaterials synthesized in this study have the potential to significantly enhance the effectiveness of tumor magnetothermal therapy.
•Improve the SAR by increasing the magnetic saturation with exchange coupling between the soft and hard magnetic phases.•Combine magnetic nanomaterials with graphene oxide to construct heat transfer channels to further improve the SAR.•Investigate Mn1-xCoxFe2O4 MNPs in a wide range of Mn and Co ratios and select the best one with highest SAR value.•Investigate magnetic properties of Mn0.5Co0.5Fe2O4-GO MNPs with different GO contents in alternating magnetic field.
Under the cyclic loading of a strong bipolar electric field, severe and rapid ferroelectric fatigue phenomena were observed in a 001.sub.c poled 0.24PIN-0.49PMN-0.27PT single crystal, where both of ...coercive field E.sub.c and remnant polarization P.sub.r decrease sharply with electric cycling in a similar trend. The ferroelectric hysteresis dynamic characteristics of the fatigued sample were investigated systemically to explore the influence of electric fatigue on hysteresis behavior. Different relationships for E.sub.c, P.sub.r, hysteresis area < A >, saturation polarization P.sub.s and back-switching polarization P.sub.bc, vs temperature T or frequency f were characterized in the temperature region from 293 to 433 K and frequency region from 0.1 to 100 Hz. Our results showed that hysteresis parameters < A > and E.sub.c decreased approximately linearly with T in the rhombohedral or tetragonal phase. However, anomalous increases of the P.sub.r and P.sub.s with T were observed in the nearly whole temperature region, which is in conflict with the previous studies. It is suggested that depinning of domains due to increase of temperature is an origin of the rejuvenation of fatigue and the increasing of P.sub.r and P.sub.s with T. Moreover, different linear scaling relations between Log < A > and Log(f) were observed at different frequency ranges, which may contribute to heterogeneous nucleation or thermally activated creep motion of domains.
In this work we report the preparation of fucan-coated magnetite (Fe3O4) nanoparticles by the co-precipitation method. These nanoparticles were characterized by scanning electron microscopy, ...transmission electron microscopy, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Mössbauer spectroscopy and magnetic measurements. The nanoparticles showed quasi-spherical morphology with mean sizes around 10nm. XRD and FT-IR confirmed the functionalization of the Fe3O4 nanoparticles with the fucan polysaccharide. Room temperature magnetization measurements and Mössbauer spectroscopy showed that the nanoparticles exhibited superparamagnetic behavior at 300K and the magnetic properties of the Fe3O4 are partly screened by the coating preventing aggregation.
•Syntheses of fucan-coated Fe3O4 nanoparticles were made by co-precipitation method.•The efficiency of polysaccharide coated was analyzed by XRD and FT-IR.•The magnetic nanoparticles mean size was 10–20nm.•The fucan-coated magnetite nanoparticles showed superparamagnetic behavior.
LaFeOsub.3 perovskite ceramics have been prepared via reaction flash technique using Fesub.2Osub.3 and Lasub.2Osub.3 as precursors. The obtained pellets have been investigated using several ...techniques. The formation of LaFeOsub.3 has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fesup.+3 ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample.
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