Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
771
result(s) for
"Magnets Experiments."
Sort by:
What makes a magnet?
Describes how magnets work and includes instructions for making a magnet and a compass.
Book
Magnets
\"Describes how magnets work and gives examples of everyday uses of magnets. Includes experiments\"-- Provided by publisher.
Book
Hardware-efficient variational quantum eigensolver for small molecules and quantum magnets
The ground-state energy of small molecules is determined efficiently using six qubits of a superconducting quantum processor.
Scalable quantum simulation
Quantum simulation is currently the most promising application of quantum computers. However, only a few quantum simulations of very small systems have been performed experimentally. Here, researchers from IBM present quantum simulations of larger systems using a variational quantum eigenvalue solver (or eigensolver), a previously suggested method for quantum optimization. They perform quantum chemical calculations of LiH and BeH
2
and an energy minimization procedure on a four-qubit Heisenberg model. Their application of the variational quantum eigensolver is hardware-efficient, which means that it is optimized on the given architecture. Noise is a big problem in this implementation, but quantum error correction could eventually help this experimental set-up to yield a quantum simulation of chemically interesting systems on a quantum computer.
Quantum computers can be used to address electronic-structure problems and problems in materials science and condensed matter physics that can be formulated as interacting fermionic problems, problems which stretch the limits of existing high-performance computers
1
. Finding exact solutions to such problems numerically has a computational cost that scales exponentially with the size of the system, and Monte Carlo methods are unsuitable owing to the fermionic sign problem. These limitations of classical computational methods have made solving even few-atom electronic-structure problems interesting for implementation using medium-sized quantum computers. Yet experimental implementations have so far been restricted to molecules involving only hydrogen and helium
2
,
3
,
4
,
5
,
6
,
7
,
8
. Here we demonstrate the experimental optimization of Hamiltonian problems with up to six qubits and more than one hundred Pauli terms, determining the ground-state energy for molecules of increasing size, up to BeH
2
. We achieve this result by using a variational quantum eigenvalue solver (eigensolver) with efficiently prepared trial states that are tailored specifically to the interactions that are available in our quantum processor, combined with a compact encoding of fermionic Hamiltonians
9
and a robust stochastic optimization routine
10
. We demonstrate the flexibility of our approach by applying it to a problem of quantum magnetism, an antiferromagnetic Heisenberg model in an external magnetic field. In all cases, we find agreement between our experiments and numerical simulations using a model of the device with noise. Our results help to elucidate the requirements for scaling the method to larger systems and for bridging the gap between key problems in high-performance computing and their implementation on quantum hardware.
Journal Article
Experiments with magnets
\"Read and Experiment is an engaging series, introducing children to scientific concepts. Explore the world of magnets with clear text, real-world examples and fun, safe step-by-step experiments. This book brings the science of magnets to life, explaining the concepts and encouraging children to be hands-on scientists.\"-- Provided by publisher.
Book
Electrical manipulation of skyrmions in a chiral magnet
Writing, erasing and computing are three fundamental operations required by any working electronic device. Magnetic skyrmions could be essential bits in promising in emerging topological spintronic devices. In particular, skyrmions in chiral magnets have outstanding properties like compact texture, uniform size, and high mobility. However, creating, deleting, and driving isolated skyrmions, as prototypes of aforementioned basic operations, have been a grand challenge in chiral magnets ever since the discovery of skyrmions, and achieving all these three operations in a single device is even more challenging. Here, by engineering chiral magnet Co
8
Zn
10
Mn
2
into the customized micro-devices for in-situ Lorentz transmission electron microscopy observations, we implement these three operations of skyrmions using nanosecond current pulses with a low current density of about 10
10
A·m
−
2
at room temperature. A notched structure can create or delete magnetic skyrmions depending on the direction and magnitude of current pulses. We further show that the magnetic skyrmions can be deterministically shifted step-by-step by current pulses, allowing the establishment of the universal current-velocity relationship. These experimental results have immediate significance towards the skyrmion-based memory or logic devices.
There has been much interest in using skyrmions for new approaches to compution, however, creating, deleting and driving skyrmions remains a challenge. Here, Wang et al demonstrate all three operations for skyrmions in tailored Co8Zn10Mn2 nanodevices using tailored current pulses.
Journal Article
Magnetic field induced quantum phases in a tensor network study of Kitaev magnets
Recent discovery of the half quantized thermal Hall conductivity in
α
-RuCl
3
, a candidate material for the Kitaev spin liquid, suggests the presence of a highly entangled quantum state in external magnetic fields. This field induced phase appears between the low field zig-zag magnetic order and the high field polarized state. Motivated by this experiment, we study possible field induced quantum phases in theoretical models of the Kitaev magnets, using the two dimensional tensor network approach or infinite tensor product states. We find various quantum ground states in addition to the chiral Kitaev spin liquid occupying a small area in the phase diagram. They form a band of emergent quantum phases in an intermediate window of external magnetic fields, somewhat reminiscent of the experiment. We discuss the implications of these results in view of the experiment and previous theoretical studies.
α
-RuCl
3
is a candidate Kitaev spin liquid but whether or not this is realised depends on the details of the magnetic interactions. Here, the authors use state-of-the-art numerical methods to predict that for a large parameter region the Kitaev phase is supplanted by nematic paramagnetic phases.
Journal Article
Anomalous electrical magnetochiral effect by chiral spin-cluster scattering
The non-collinear spin configurations give rise to many nontrivial phenomena related to the Berry phase. They are often related to the vector and scalar spin chiralities. The scalar spin chirality leads to the topological Hall effect in metals, while the vector spin chirality to the ferroelectricity of spin origin, i.e., multiferroics in insulators. However, the role of the vector spin chirality in conducting systems has not yet been elucidated. Here we show theoretically that the spin correlation with vector spin chirality in chiral magnets scatters electrons asymmetrically, resulting in nonreciprocal transport phenomena, i.e., electrical magnetochiral effect (eMCE). This asymmetric scattering appears in the leading-order scattering term, implying a large nonreciprocity in the charge and spin currents. We find that the temperature and magnetic field dependence of the eMCE reproduces that observed in MnSi. Our results reveal the microscopic mechanism of eMCE and its potential in producing a large nonreciprocal response.
The microscopic mechanism for nonreciprocity of electron transport in bulk materials remains less well understood. Here, the authors show that asymmetric electron scattering by two-spin clusters induce nonreciprocal current (electric current proportional to the square of the electric field) in magnetic metals.
Journal Article
Experimental Investigation on the Surface Formation Mechanism of NdFeB during Diamond Wire Sawing
Diamond wire sawing is widely used in processing NdFeB rare earth permanent magnets. However, it induces periodic saw marks and fracture chipping pits, which severely affect the flatness and surface quality of the products. In this study, the lateral motion of the diamond wire was monitored to determine the surface formation mechanism. Then, a white light interferometer and an SEM were used to observe the sawed surface profile. Finally, the surface quality was quantitatively studied by identifying the area rate of fracture chipping pits with an image recognition MATLAB script. According to the observation results, the calculation formula of PV which is related to the process parameters was deduced. Additionally, by combining the fracture rate and wire vibration, a novel method was proposed to investigate the optimal process parameters. It can be found that the surface quality sawed at P = 0.21 MPa, vf = 0.2 mm/min, and vs = 1.8 m/s remains better than when sawed at P = 0.15 MPa, vf = 0.1 mm/min, and vs = 1.8 m/s, which means the sawing efficiency can be doubled under such circumstances, i.e., when the surface quality remains the same.
Journal Article
An Innovative H-Type Flux Switching Permanent Magnet Linear Generator for Thrust Force Enhancement
In this paper, two H-type flux switching permanent magnet linear generators with outer-translator and inner-translator configurations are discussed and compared to a more conventional flux switching topology. The stators consist of H-Type modules housing circumferential coils and are surrounded by two annular permanent magnets. In conventional flux switching machines, the windings are orientated perpendicular to the direction of motion and the conductors twist around the magnets. In H-type topologies, the orientation of the windings is in the same plain as the magnets and parallel to the direction of motion, resulting in an increase in flux linkage. The proposed topologies are designed for a low operating speed and a large magnetic gap, as found in wave energy converters. All topologies are optimized using the Taguchi optimization approach with the goals of reducing force ripple and increasing the average thrust force and efficiency. The 2D finite element method (FEM) is used in the optimization stage to calculate the optimized parameters of the presented generators, after which the optimized structures are simulated using 3D FEM, and the results are extracted. The results of the optimization show that the H-type topologies deliver a 20% higher shear stress whilst offering an easier to assemble structure.
Journal Article