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This study explores Hall transport phenomena by expanding upon prior research on magnetic disk arrays (MDAs). We examine the dynamics of charged particles using collision models akin to those in Lorentzian plasma. Previously, we derived transport coefficients under isotropic and mono-kinetic conditions. In this study, we adopt an anisotropic framework, enhanced by Fourier transformation, and employ the local Maxwellian distribution function. These assumptions allow us to calculate the Hall diffusivity, electrical conductivity, and thermal Hall conductivity tensors. Our findings contribute to a deeper understanding of the Hall transport in magnetic disk arrays and chiral active systems.

Large-amplitude magnetization dynamics is substantially more complex compared to the low-amplitude linear regime, due to the inevitable emergence of nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear damping enhancement, which imposes strict limitations on the operation and efficiency of magnetic nanodevices. In particular, nonlinear damping prevents excitation of coherent magnetization auto-oscillations driven by the injection of spin current into spatially extended magnetic regions. Here, we propose and experimentally demonstrate that nonlinear damping can be controlled by the ellipticity of magnetization precession. By balancing different contributions to anisotropy, we minimize the ellipticity and achieve coherent magnetization oscillations driven by spatially extended spin current injection into a microscopic magnetic disk. Our results provide a route for the implementation of efficient active spintronic and magnonic devices driven by spin current. Nonlinear damping enhancement imposes strict limitations on the operation and efficiency of magnetic nano-devices. Here the authors show that nonlinear damping can be controlled by the ellipticity of magnetization precession, which provides a route for the implementation of efficient active spintronic and magnonic devices driven by spin current.

A novel magnetic abrasive finishing (MAF) technique employing a rotating magnetic disc is developed to address the issue of uneven polishing on large-sized slender tubes. The method involves arranging a series of magnetic poles in an S–N-S–N configuration on a pair of rotating discs, with the tubes being processed fed between the gap of the two discs. This approach results in a 246% increase in finishing efficiency compared to traditional MAF processes, where only the workpiece rotates. The finishing characteristics are determined by the interaction of the magnetic abrasive particles (MAPs) with the tube’s outer surface. This interaction is regulated by the magnetic field distribution on the surface and the contact trajectory density of the MAPs. The S–N-S–N magnetic pole configuration defines the magnetic field characteristics, which in turn control the magnetic force and the contact trajectory required for the MAPs behavior. An experimental design method was employed to determine the optimal process for a 5-m-long zirconium alloy cladding tube, utilizing a high-speed feeding rate of 5 m/min. Even at high feed rates, the tube’s surface can be processed with dense trajectories and consistent results. The outer surface roughness of the zirconium alloy cladding tube was reduced by 31%, from 0.356 to 0.247 µm, after a single-pass treatment. Following MAF processing, the final roughness can reach 0.126 µm.

Two-dimensional magnetic systems with continuous spin degrees of freedom exhibit a rich spectrum of thermal behaviour due to the strong competition between fluctuations and correlations. When such systems incorporate coupling via the anisotropic dipolar interaction, a discrete symmetry emerges, which can be spontaneously broken leading to a low-temperature ordered phase. However, the experimental realisation of such two-dimensional spin systems in crystalline materials is difficult since the dipolar coupling is usually much weaker than the exchange interaction. Here we realise two-dimensional magnetostatically coupled XY spin systems with nanoscale thermally active magnetic discs placed on square lattices. Using low-energy muon-spin relaxation and soft X-ray scattering, we observe correlated dynamics at the critical temperature and the emergence of static long-range order at low temperatures, which is compatible with theoretical predictions for dipolar-coupled XY spin systems. Furthermore, by modifying the sample design, we demonstrate the possibility to tune the collective magnetic behaviour in thermally active artificial spin systems with continuous degrees of freedom. Magnetic metamaterials can be designed to provide models of frustrated systems that allow theoretical predictions to be experimentally tested. Here the authors realise a 2D XY model with dipolar interactions and find behaviour consistent with predictions of a low-temperature ordered state.

We studied the bonding mechanism of ultrathin perfluoropolyether (PFPE) lubricant (Fombline Z -tetraol and Moresco D-4OH) films with hydroxyl end groups by measuring the bonding film thickness after ultraviolet (UV) irradiation. Nonfunctional PFPE lubricants (Z-03 and D2 N) were compared to two types of functional PFPE lubricants. The bonded thickness of both functional lubricants increased after a short period of UV irradiation, whereas that of the nonfunctional lubricants did not increase after the same treatment. This result suggests the occurrence of three kinds of mechanisms. First, Z -tetraol and D-4OH bond because of the photodissociation of the end groups by the UV light. Second, they bond because of the interaction between the end groups and the photoelectron from the carbon surface generated by UV irradiation. Third, they bond because of the photodissociation of the main chain by the UV light. In contrast, the dynamic reaction coordinate calculations suggest that the end groups in the PFPE lubricant dissociate because of the electron capture by the lubricant. As a result, we infer that the bonding of PFPE lubricant films with hydroxyl end groups on magnetic disks occurs by selective dissociation of the end groups because of UV irradiation.

A meron is a classical topological soliton having a half topological charge. It could be materialized in a magnetic disk. However, it will become a quantum mechanical object when its size is of the order of nanometers. Here, we propose to use a nanoscale meron in a magnetic nanodisk as a qubit, where the up and down directions of the core spin are assigned to be the qubit states 0 and 1 . We first numerically show that a meron with the radius containing as small as 7 spins can be stabilized in a ferromagnetic nanodisk classically. Then, we show theoretically that universal quantum computation is possible based on merons by explicitly constructing the arbitrary phase-shift gate, Hadamard gate, and CNOT gate. They are executed by applying a magnetic field or spin-polarized current. Our results may be useful for the implementation of quantum computation based on topological spin textures in nanomagnets. Merons are spin textures with a half-unit topological charge found in chiral magnetic materials. Here, the authors show that merons with nanometer-scale size are stable and can be used to perform quantum computing gate operations by applying a magnetic field or spin-polarized current.

We compute the Hofer–Zehnder capacity of magnetic disc tangent bundles over constant curvature surfaces. We use the fact that the magnetic geodesic flow is totally periodic and can be reparametrized to obtain a Hamiltonian circle action. The oscillation of the Hamiltonian generating the circle action immediately yields a lower bound of the Hofer–Zehnder capacity. The upper bound is obtained from Lu’s bounds of the Hofer–Zehnder capacity using the theory of pseudo-holomorphic curves. In our case, the gradient spheres of the Hamiltonian H will give rise to the non-vanishing Gromov–Witten invariant.

Structural ordering in the concentrated magnetic colloids containing 50 × 5 nm hard magnetic disc-like SrFe 12 O 19 nanoparticles was investigated by cryogenic scanning electron microscopy, optical microscopy, magnetic measurements, and small-angle X-ray scattering. It was revealed that macroscopically homogeneous magnetic liquid consists of dynamic threads of stacked nanoparticles. The threads align into quasiperiodic arrays with the distances between individual threads of a few micrometers. They also can form pseudodomain structures with ~ 90° domain boundaries realized through T-type thread interconnects. The effects of magnetic attraction and electrostatic repulsion on the equilibrium interplatelet distance in the threads were studied. It was demonstrated that this distance can be tuned by the control of the particles charge and electric double layer screening from Stern layer thickness (~ 1 nm) to tens of nanometers. It was shown that the permanent magnetic field is not able to cause any structural changes in the ordered magnetic liquid phase, while alternating field draws particles apart by their vibrations. External variation of interparticle distance up to 6% was achieved using an alternating magnetic field of low intensity. Experimental data were complemented by the theoretical models of screened electrostatic interactions between spherical and platelike magnetic particles. The last model provides good predictive power and correlates with the experimental data. The stabilization energy of the condensed phase in the order of 1–10 k B T was derived from the model. An approach allows controlling of an equilibrium interparticle distance and interparticle distance distribution by adjusting the magnetization and surface charge of the particles as well as the ionic strength of the solvent.

The paper deals with the issue of induced EMF localization in a Faraday's unipolar generator which is a revolving magnetic disk with its center and periphery connected by a conductor. Attention has also been given to the linear DC generator consisting of a long magnet and a conductor. Functioning as a closed loop, this conductor moves within the magnetic field of the magnet, the ends sliding on its surfaces. It is shown that in a linear unipolar generator the EMF is induced in a conductor irrespective of a reference frame chosen. Reasons are given in favour of the fact that when a magnetic disk is revolving, the EMF is induced in a stationary conductor of a unipolar generator.

Reducing the fly-height between the head and disk to less than 1 nm with high reliability is necessary to improve the recording density of magnetic disks. Therefore, the mechanism of the head touchdown (TD) phenomenon, particularly the surfing state after the TD, needs to be understood. Assuming that the contact sliding on the sub-nanometer asperities, covered with a monolayer lubricant film, generates the lubrication film forces and reduces the surface forces, the present study shows that numerical simulations of a one-degree-of-freedom slider model can be used to understand various TD phenomena, including surfing conditions. The three different TD behaviors of a commercial head slider were explained by the differences in the rate of generation of the lubrication film force after the TD and initial surface force. The parametric studies demonstrated that surfing states could be generated at a separation of more than three times the standard deviation of the asperity height by increasing the surface force and magnitude of the disk-waviness, thereby suggesting the possibility of quasi-contact recording.