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We present a quantum dynamics study on the isotope effects of hydrogen transfer isomerization in the formic acid dimer, and this is achieved by multidimensional dynamics calculations with an efficient quantum mechanical theoretical scheme developed by our group, on a full-dimensional neural network ab initio potential energy surface. The ground-state and fundamental tunneling splittings for four deuterium isotopologues of formic acid dimer are considered, and the calculated results are in very good general agreement with the available experimental measurements. Strong isotope effects are revealed, the mode-specific fundamental excitation effects on the tunneling rate are evidently influenced by the deuterium substitution of H atom with the substitution on the OH bond being more effective than on the CH bond. Our studies are helpful for acquiring a better understanding of isotope effects in the double-hydrogen transfer processes. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions are topological quasiparticles with nanoscale size and high mobility, which have potential applications in information storage and spintronic devices. Here, we computationally investigate the dynamics of isolated skyrmions in a ferromagnetic racetrack, where magnetic properties of the edges are enhanced and modified, forming a channel with lower magnetic anisotropy for skyrmion motion. It is found that the rectangular notch at the edge can have a pinning effect on the skyrmion and enrich the dynamics of the skyrmion. Based on the racetrack with modified edges and the notch, we design a racetrack that realizes the skyrmionic logic AND, OR, and NOT gates as well as the diode in the same magnetic racetrack. It is found that the driving current density could be much smaller than those used in previous designs of skyrmion-based logic gates. By slightly altering the shape of the racetrack, we also design the NAND and NOR gates. Finally, we study the feasibility of our design at finite temperatures. Our results may contribute to the design of nonvolatile spintronic devices with integrated multiple functions and ultra-low energy consumption. [ABSTRACT FROM AUTHOR]

Antiferromagnets are promising materials for future spintronic applications due to their unique properties including zero stray fields, robustness vs external magnetic fields, and ultrafast dynamics, which have attracted extensive interest in recent years. In this work, we investigate the dynamics of isolated skyrmions in an antiferromagnetic nanotrack with a voltage-gated region. It is found that the skyrmion can be jointly controlled by the driving current and the voltage-controlled magnetic anisotropy gradient. We further propose a design of logic computing gates based on the manipulation of antiferromagnetic skyrmions, which is numerically realized combining several interactions and phenomena, including the spin Hall effect, voltage-controlled magnetic anisotropy effect, skyrmion–skyrmion interaction, and skyrmion–edge interaction. The proposed logic gates can perform the basic Boolean operations of the logic AND, OR, NOT, NAND, and NOR gates. Our results may have a great impact on fundamental physics and be useful for designing future nonvolatile logic computing devices with ultra-low energy consumption and ultra-high storage density. [ABSTRACT FROM AUTHOR]

We show a topological spin texture called "bimeronium" in magnets with in-plane magnetization. It is a topological counterpart of skyrmionium in perpendicularly magnetized magnets and can be seen as a combination of two bimerons with opposite topological charges. We report the static structure and spin-orbit-torque-induced dynamics of an isolated bimeronium in a magnetic monolayer with frustrated exchange interactions. We study the anisotropy and magnetic field dependences of a static bimeronium. We also explore the bimeronium dynamics driven by the damping-like spin-orbit torque. We find that the bimeronium shows steady rotation when the spin polarization direction is parallel to the easy axis. Moreover, we demonstrate the annihilation of the bimeronium when the spin polarization direction is perpendicular to the easy axis. Our results are useful for understanding the fundamental properties of bimeronium structures and may offer an approach to build bimeronium-based spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic skyrmionium can be used as a nanometer-scale non-volatile information carrier, which shows no skyrmion Hall effect due to its special structure carrying zero topological charge. Here, we report the static and dynamic properties of an isolated nanoscale skyrmionium in a frustrated magnetic monolayer, where the skyrmionium is stabilized by competing interactions. The frustrated skyrmionium has a size of about 10 nm, which can be further reduced by tuning perpendicular magnetic anisotropy or the magnetic field. It is found that the nanoscale skyrmionium driven by the damping-like spin-orbit torque shows directional motion with a favored Bloch-type helicity. A small driving current or magnetic field can lead to the transformation of an unstable Néel-type skyrmionium to a metastable Bloch-type skyrmionium. A large driving current may result in the distortion and collapse of the Bloch-type skyrmionium. Our results are useful for the understanding of frustrated skyrmionium physics, which also provide guidelines for the design of spintronic devices based on topological spin textures. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions are promising building blocks for developing information storage and computing devices. It can be stabilized in a ferromagnetic thin film with the Dzyaloshinskii-Moriya interaction (DMI). The moving ferromagnetic skyrmion may show the skyrmion Hall effect, that is, the skyrmion shows a transverse shift when it is driven by a spin current. Here, we numerically and theoretically study the current-driven dynamics of a ferromagnetic nanoscale skyrmion in the presence of the anisotropic DMI, where the skyrmion has an elliptical shape. The skyrmion Hall effect of the elliptical skyrmion is investigated. It is found that the skyrmion Hall angle can be controlled by tuning the profile of the elliptical skyrmion. Our results reveal the relation between the skyrmion shape and the skyrmion Hall effect, which could be useful for building skyrmion-based spintronic devices with a preferred skyrmion Hall angle. Also, our results provide a method for the minimization of the skyrmion Hall angle for applications based on in-line motion of skyrmions. [ABSTRACT FROM AUTHOR]

Provides information on a study which reported the preparation, microstructure, magnetic properties and the temperature dependence of lanthanum-zinc substituted strontium ferrite thin films. Experimental procedures; Results and discussions.

Skyrmion-based spin torque nano-oscillators are potential next-generation microwave signal generators. However, ferromagnetic skyrmion-based spin torque nano-oscillators cannot reach high oscillation frequencies. In this work, we propose to use the circular motion of an antiferromagnetic skyrmion to create an oscillation signal in order to overcome this obstacle. Micromagnetic simulations demonstrate that the antiferromagnetic skyrmion-based spin torque nano-oscillators can produce high frequencies (tens of GHz). Furthermore, the speed of the circular motion for an antiferromagnetic skyrmion in a nanodisk is analytically derived, which agrees well with the results of numerical simulations. Our findings are useful for the understanding of the inertial dynamics of an antiferromagnetic skyrmion and the development of future skyrmion-based spin torque nano-oscillators. [ABSTRACT FROM AUTHOR]

Spintronic devices such as magnetic random access memory and domain wall (DW) memory are attracting significant attention. Spin-field effect transistor devices have been proposed and researched for logic applications. In domain wall memory, the information is stored in magnetic domain states, which can be moved with a current above a certain threshold value. So far, the domain wall motion is only determined by the current density for most of the DW devices. Here, we demonstrate experimentally that a significant change in domain wall mobility can be achieved by applying a gate voltage. By applying a positive gate voltage, we show that the threshold current density for DW motion can be reduced by more than 10%. By choosing a suitable operating current, the domain wall motion can be switched on or off by the use of a gate voltage. These results are promising for designing high performance domain wall based transistor devices with faster operation speed and lower power consumption. [ABSTRACT FROM AUTHOR]

An ultrathin MgO/Fe seed layer was introduced to manipulate the crystal orientation and crystallinity of Fe/MgO/Fe trilayers. The crystallographic properties and magnetic properties of the trilayer are investigated. It is concluded that the texture of the MgO layer is strongly dependent on the texture of the Fe layer. (001) oriented Fe layer can assist the growth of (001) oriented MgO barrier upon annealing. A 0.5 nm MgO seed layer can introduce (001) orientation in the following Fe layer. It is also found that the crystal orientation of the Fe/MgO/Fe trilayer is independent of the initial Fe seed layer thickness. However, the crystallinity of both the Fe layer and the MgO layer is dependent on the initial Fe seed layer. [ABSTRACT FROM AUTHOR]

The longitudinal CoCrPt thin films have been prepared on CrW underlayer at room temperature. The dependence of CoCrPt’s structure and magnetic properties on the Pt content was investigated. The addition of platinum element in the CoCrPt magnetic layer increases the lattice constant and longitudinal coercivity of the CoCrPt thin films. The coercivity mechanism of the CoCrPt thin film is analyzed by using the micromagnetic models, with careful discussions of the uniaxial crystalline anisotropy and the magnetostriction. It is found that the magnetostriction effects play an important role on the coercivity mechanisms when the Pt content is more than 15 at. % Pt concentrate. [ABSTRACT FROM AUTHOR]

New soft magnetic head materials, the nanocrystalline FeCoAlOC thin films, were prepared by introducing C element in epoxy resin during rf sputtering of FeCoAlO films. When Al2O3 was cosputtered with FeCo, soft magnetic properties of thin films were highly improved: the coercive force decreases from dozen of oersted to several oersted (Hch∼4.8 Oe and Hce∼6.5 Oe). With further addition of carbon, the thin films exhibit excellent soft magnetic properties and good high frequency response: the coercivity is as low as 1.0 Oe, with saturation Bs>20 kG, permeability μ′>500 when f≤1.0 GHz, and cutoff frequency around 1.7 GHz. The measurement of microstructure shows that the good magnetic properties are correlated with the small gain size of film. [ABSTRACT FROM AUTHOR]

The crystallographic and magnetic properties of sub-10-nm Nd2Fe14B films have been investigated. It is found that the magnetization reversal mechanism is changed in Nd–Fe–B films with the decrease of film thickness. Films with thickness greater than 10 nm show domain-wall-motion type of behavior. Strong exchange coupling between the grains makes the magnetic domain wall easily propagate in the films. Films with thickness of 4 nm show the Stoner-Wohlfarth particle behavior. The initial magnetization process is magnetization rotation. This is also verified by angular dependence of the coercivity. [ABSTRACT FROM AUTHOR]

The magnetic properties of multilayer composed of Fe65Co35 and thin layers of Co (less than 5 nm) have been investigated. It is found that the microstructure, crystallographic texture, and magnetic softness of the multilayers depended on the initial layer. Multilayers with saturation magnetic induction higher than 23 kG and hard axis coercivity smaller than 2 Oe have been successfully prepared by using Co as the initial layer. Furthermore, the structure provided an effective process to tailor the in-plane magnetic anisotropy field without deteriorating the magnetic softness of the multilayers. [ABSTRACT FROM AUTHOR]

We have successfully prepared Sr-ferrite dot arrays with perpendicular magnetic anisotropy by electron beam lithography. Virgin magnetic configurations detected by magnetic force microscopy (MFM) show single domain configuration for a 0.5 μm dot, while multidomain configurations are found for larger dots. The magnetization reversal mechanism in dots larger than 0.5 μm is found to be domain wall motion. While the magnetization reversal mechanism in 0.5 μm dots is found to be magnetization rotation. A normalized dc demagnetization remanence curve (DCD) measured by a superconducting quantum interference device (SQUID) indicates that with a decrease of dot size, the DCD curve is approaching the curve predicted by the coherent rotation model. Both MFM and SQUID results indicate that the single-domain dots reversed individually free from interdot magnetostatic coupling. [ABSTRACT FROM AUTHOR]

La–Zn substituted Sr-ferrite thin films were prepared by rf diode sputtering. The magnetic and crystallographic properties of the films were investigated by vibrating sample magnetometry and x-ray diffractometry. It is found that the texture of the films sensitively depends on the amount of substitution. Both the saturation magnetization M[sub s] and coercivity H[sub c] increase with the increase of La–Zn substitution. The increase of H[sub c] is caused, in part, by the increase of K[sub 1] due to the substitution. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the effect of underlayer for Ba-ferrite sputtered films on c-axis orientation. Improvement of crystallinity for hexagonal M phase; Preparation of the BaM films on the amorphous underlayer.

In this research work, ferrite nanoparticles with composition of SrFe12-x(Ni0.5Co0.5Ti)x/2O19 (x = 0-2.5 in a step of 0.5) were synthesized by a reverse micelle. Multiwalled carbon nanotubes (MWCNT) were also functionalized by employing poly(acrylic acid). Then the ferrite nanoparticles were deposited on the functionalized surface of carbon nanotubes by hetero-coagulation process. The volume percentage of carbon nanotubes was kept constant at 8 vol. % for synthesizing nanocomposites. The site preference of substituted cations in ferrite crystal structure was determined by 57Fe Mössbauer spectroscopy. It was proved that the substituted cations were distributed in 12 k crystallographic sites. The morphology of ferrite dot array on carbon nanotubes was studied by field emission scanning electron microscopy (FESEM). Quantum Device MPMS-5S SQUID magnetometer was used to probe the variation of magnetization with applied magnetic field. It was found that with an increase in substitution content, the saturation of magnetization and coercivity decrease. [ABSTRACT FROM AUTHOR]

By introducing artificial pinning sites to locally modify coercivity in perpendicularly magnetized TbFeCo wires, strip domains were constructed without expense of specimen damage. The construction of strip domains with well-defined shape and controllable number enables a determination of magneto-resistance contributing from singe domain wall. Contrast to crystalline materials, a rather high domain wall magneto-resistance ratio near 20% was found at room temperature, indicating the amorphous TbFeCo is a potential candidate for spintronic devices. [ABSTRACT FROM AUTHOR]

5 × 25 mm FeCoAlO gradient composition thin film was prepared with composite target by using RF magnetron sputtering. The Al-O composition gradient along the length direction of the film was introduced by Al2O3 chips asymmetrically arrayed on a Fe70Co30 target disk. The film was divided into five equal segments. All samples showed a low coercive force Hc of 4 - 8 Oe. The saturation magnetization 4πMs increased continuously from 17.3 kGs for sample 1 (has more Al-O content) to 19.7 kGs for sample 5 and it was consistent with the increasing of Fe-Co composition. Meanwhile, these samples showed different anisotropy behaviors relating with Al-O composition. The sample 1 exhibited the same magnetization curve along the directions of G| and G⊥ (G| and G⊥ are parallel and perpendicular to the direction of the Al-O composition gradient, respectively). In both of G| & G⊥ directions, the sample 1 showed a resonance frequency (fr) of around 2.6 - 3.0 GHz, while, in G| direction, it showed a high value of real permeability μ′. The sample 5 exhibited a distinct in-plane uniaxial anisotropy and a good high-frequency response of 3.0 GHz resonance frequency. So these films having gradient composition exhibit are suggested for the use in integrated magnetic devices working in the GHz frequency range. [ABSTRACT FROM AUTHOR]

FeCoAlO thin films with good soft magnetic properties were fabricated by using RF magnetron sputtering. In order to obtain good high-frequency performance, the in-plane uniaxial anisotropy was tuned by combining the effects of in situ magnetic field and the gradient of Al-O concentration. The composition gradient was controlled by using an asymmetric target and different Ar gas flow rates changing from 5 sccm to 17.5 sccm. It was found that at the range of Ar gas flow rate from 7.5 sccm to 15 sccm, the films showed an excellent high-frequency performance: the resonance frequency was beyond 3.0 GHz and the real permeability μ′ had a high value of ∼200 at low-frequency side. In particular, the film prepared at the Ar gas flow rate of 15 sccm showed a resonance frequency of 4.0 GHz. Large resonance frequency can be attributed to the high in-plane uniaxial anisotropy field which was induced by stress and the external magnetic field. The high values of permeability and resonance frequency enable the FeCoAlO thin films to be one of the important candidates for microwave applications. [ABSTRACT FROM AUTHOR]

Large-scale carbon nanotubes (CNTs)/substituted strontium ferrite nanocomposites have been fabricated by hetero-coagulation. The structure and morphology of nanoparticles and nanocomposites were evaluated by high-resolution transmission electron microscopy (HRTEM). HRTEM confirmed that strontium ferrite was successfully attached to carbon nanotubes. The vibrating sample magnetometer (VSM) confirmed the relatively strong dependence of saturation magnetization with the volume percentage of multi-walled carbon nanotubes (MWCNTs). Reflection loss of nanocomposites at 12-18 GHz was evidently enhanced, as compared to that of strontium ferrite nanoparticles. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs. It was proved that the microwave absorbing bandwidth was modulated simply by manipulating the thickness of nanocomposites. Reflection loss evaluations indicate that the nanocomposites display a great potential application as wide-band electromagnetic wave absorbers. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties of Nd-Fe-B films with thicknesses from 100 nm to 3 nm have been investigated. All the films show excellent perpendicular magnetic anisotropy with a squareness ratio of 1 in the perpendicular direction and almost zero coercivity in the in-plane direction. Of particular interest is that the initial magnetization curves sensitively depended on the film thickness. Films thicker than 15 nm show steep initial magnetization curve. Although the films have coercivities larger than 21 kOe, the films can be fully magnetized from the thermally demagnetized state with a field as small as 5 kOe. With the decrease of film thickness to 5 nm, the initial magnetization curve becomes flat. The evolution of initial magnetization curves with film thickness can be understood by the microstructure of the films. Films with thickness of 15 nm show close-packed grains without any intergranular phases. Such microstructures lead to steep initial magnetization curves. On the other hand, when the film thickness decreased to 3 nm, the film thickness became nonuniform. Such microstructure leads to flat initial magnetization curves. [ABSTRACT FROM AUTHOR]

In this research work, magnetic multi-walled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mn-Co-Ti-substituted barium ferrite nanoparticles onto the surface of MWCNTs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to demonstrate the successful attachment of ferrite nanoparticles to MWCNTs. Vibrating sample magnetometry (VSM) confirmed the relatively strong dependence of saturation magnetization on the volume percentage of MWCNTs. Microwave absorption of the MWCNTs/doped barium ferrite (BaM) nanocomposites is evidently enhanced compared to that of pure MWCNTs and ferrite nanoparticles. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs in nanocomposites. [ABSTRACT FROM AUTHOR]

Zn1 - xCoxFe2O4 (x = 0-1 in a step of 0.2) nanoparticles with different range of particle size including 5-10 nm and 200-250 nm have been prepared by sol-gel process. Mössbauer spectra at room temperature indicated that, with increasing cobalt content, there is a transition from paramagnetic to magnetically ordered-ferrimagnetic state. Magnetic properties were measured at 300 and 10 K using a Quantum Design MPMS-5S SQUID magnetometer. It was found that with an increase in cobalt content the saturation magnetization and coercivity increase. [ABSTRACT FROM AUTHOR]

The soft magnetic FeCoAlO thin films with different response at high frequency were prepared by using RF magnetron sputtering. Two different configurations of the sputtering targets were used: the Al2O3 chips were placed on Fe70Co30 disk either uniformly dispersed on the sputtering area (Target-A) or dispersed on the half side of the sputtering area (Target-B). It was found that, although, the films deposited from both of Target A and B possessed good soft magnetic properties and in-plane uniaxial magnetic anisotropy, they showed different behaviors at high frequency. The films deposited by using Target-A have mean permeability of 500 and a cut-off frequency (fr) of around 780 MHz, while the films deposited by using Target-B have mean permeability of 200 and a fr of 3.4 GHz. The higher fr of the later corresponds to the higher uniaxial anisotropic field in the films deposited by using the Target-B, which due to an extra anisotropy induced by the stress resulted from gradient of the Al-O composition. By adjusting the configuration of Target-B, the permeability & fr can be tuned to satisfy the different requirements for certain industrial applications. [ABSTRACT FROM AUTHOR]

The FePt films were deposited with [Fe/Pt]n multilayer structure on preheated Corning 1737F glass substrate using pure Fe and Pt target in a CMS-18 sputtering system. The dependence of FePt's texture and magnetic properties on the multilayer structure was investigated. The XRD patterns indicate that (111) texture is dominant for all [Fe/Pt]n (n = 8, 16, 20, 32) multilayer films. However, the measured M-H loops show that the perpendicular anisotropy is greatly enhanced in samples with n = 16, 20, and 32. The origin of the increased perpendicular anisotropy of [Fe/Pt]n multilayer films is related to the contributions of the interfaces, which will be analyzed using the micromagnetic models, with careful discussions of the crystalline and interface anisotropies. Finally, it is confirmed that the Fe/Pt interfaces favor the perpendicular orientation in the multilayer structure. [ABSTRACT FROM AUTHOR]

A magnetic skyrmionium is a skyrmion-like structure, but carries a zero net skyrmion number which can be used as a building block for non-volatile information processing devices. Here, we study the dynamics of a magnetic skyrmionium driven by propagating spin waves. It is found that the skyrmionium can be effectively driven into motion by spin waves showing a tiny skyrmion Hall effect, whose mobility is much better than that of the skyrmion at the same condition. We also show that the skyrmionium mobility depends on the nanotrack width and the damping coefficient and can be controlled by an external out-of-plane magnetic field. In addition, we demonstrate that the skyrmionium motion driven by spin waves is inertial. Our results indicate that the skyrmionium is a promising building block for building spin-wave spintronic devices. [ABSTRACT FROM AUTHOR]