Search results for "Magnetism"
showing 10 items of 1934 documents
Magnetic Gradiometer for Detection of Zero- and Ultralow-Field Nuclear Magnetic Resonance
2019
Magnetic sensors are important for detecting nuclear magnetization signals in nuclear magnetic resonance (NMR). As a complementary analysis tool to conventional high-field NMR, zero- and ultralow-field (ZULF) NMR detects nuclear magnetization signals in the sub-microtesla regime. Current ZULF NMR systems are always equipped with high-quality magnetic shieldings to ensure that ambient magnetic field noise does not dwarf the magnetization signal. An alternative approach is to separate the magnetization signal from the noise based on their differing spatial profiles, as can be achieved using a magnetic gradiometer. Here, we present a gradiometric ZULF NMR spectrometer with a magnetic gradient …
Anisotropic skyrmion diffusion controlled by magnetic-field-induced symmetry breaking
2021
The diffusion of particles has wide repercussions, ranging from particle-based soft-matter systems to solid-state systems with particular electronic properties. Recently, in the field of magnetism, the diffusion of magnetic skyrmions, topologically stabilized quasiparticles, has been demonstrated. Here, we show that, by applying a magnetic in-plane field, and therefore, breaking the symmetry of the system, skyrmion diffusion becomes anisotropic, with faster diffusion parallel to the field axis and slower diffusion perpendicular to it. We furthermore show that the absolute value of the applied magnetic in-plane field controls the absolute values of the diffusion coefficients, so that one can…
Monte Carlo studies ofd= 2 Ising strips with long-range boundary fields
2000
A two-dimensional Ising model with nearest-neighbour ferromagnetic exchange confined in a strip of width L between two parallel boundaries is studied by Monte Carlo simulations. `Free' boundaries are considered with unchanged exchange interactions at the boundary but long-range boundary fields of the form H (n ) = ? h [n -3 - (L - n + 1) -3 ], where n = 1, 2, ... ,L labels the rows across the strip. In the case of competing fields and L , the system exhibits a critical wetting transition of a similar type as in the well studied case of short-range boundary fields. At finite L , this wetting transition is replaced by a (rounded) interface localization-delocalization transition at Tc (h , L )…
Spin eigenexcitations of an antiferromagnetic skyrmion
2019
We theoretically predict and classify the localized modes of a skyrmion in a collinear uniaxial antiferromagnet and discuss how they can be excited. As a central result, we find two branches of skyrmion eigenmodes with distinct physical properties characterized by being low or high energy excitations. The frequency dependence of the low-energy modes scales as $R_0^{-2}$ for skyrmions with large radius $R_0$. Furthermore, we predict localized high-energy eigenmodes, which have no direct ferromagnetic counterpart. Except for the breathing mode, we find that all localized antiferromagnet skyrmion modes, both in the low and high-energy branch, are doubly degenerated in the absence of a magnetic…
Minkowskian description of polarized light and polarizers.
2002
A conventional Stokes description of polarized light is considered in a four-dimensional Lorentzian space, developing a seminal idea of Paul Soleillet [Ann. Phys. (Paris) 12, 23 (1929)]. This provides a striking interpretation for the degree of polarization and the Stokes decomposition of light beams. Malus law and reciprocity theorems for polarizers are studied using this Lorentzian formalism.
Critical behavior in quantum spin chains with composite spin
1989
Composite spin models are constructed such that, by varying two parameters, they interpolate between the spin-(1/2 antiferromagnetic Heisenberg chain and a number of spin-1 models. These include the usual Heisenberg model, the integrable spin-1 model, and the model with an exact valence-bond ground state. Finite-chain calculations are performed on the composite spin model to study its criticality, and to find if the integrable spin-1 model is a multicritical point with a finite gap generated away from it. We find indications for an extended gapless region.
Toward multifunctional molecular cells for quantum cellular automata: exploitation of interconnected charge and spin degrees of freedom
2021
We discuss the possibility of using mixed-valence (MV) dimers comprising paramagnetic metal ions as molecular cells for quantum cellular automata (QCA). Thus, we propose to combine the underlying idea behind the functionality of QCA of using the charge distributions to encode binary information with the additional functional options provided by the spin degrees of freedom. The multifunctional ('smart') cell is supposed to consist of multielectron MV d(n)-d(n+1)-type (1 ≤ n ≤ 8) dimers of transition metal ions as building blocks for composing bi-dimeric square planar cells for QCA. The theoretical model of such a cell involves the double exchange (DE), Heisenberg-Dirac-Van Vleck (HDVV) excha…
Rigid motions relative to an observer:L-rigidity
1996
A new definition of rigidity,L-rigidity, in general relativity is proposed. This concept is a special class of pseudorigid motions and therefore it depends on the chosen curveL. It is shown that, for slow-rotation steady motions in Minkowski space, weak rigidity andL-rigidity are equivalent. The methods of the PPN approximation are considered. In this formalism, the equations that characterizeL-rigidity are expressed. As a consequence, the baryon mass density is constant in first order, the stress tensor is constant in the comoving system, the Newtonian potential is constant along the lineL, and the gravitational field is constant along the lineL in the comoving system.
Evolution of Mixed Dirac Particles Interacting with an External Magnetic Field
2007
We study in the framework of relativistic quantum mechanics the evolution of a system of two Dirac neutrinos that mix with each other and have non-vanishing magnetic moments. The dynamics of this system in an external magnetic field is determined by solving the Pauli-Dirac equation with a given initial condition. We consider first neutrino spin-flavor oscillations in a constant magnetic field and derive an analytical expression for the transition probability of spin-flavor conversion in the limit of small magnetic interactions. We then investigate ultrarelativistic neutrinos in an transversal magnetic field and derive their wave functions and transition probabilities with no limitation for …
Rigour and Rigidity: Systematics on particle physics D6-brane models on Z(2)xZ(6)
2014
We launch a systematic search for phenomenologically appealing string vacua with intersecting D-branes on the promising T6/Z(2)xZ(6)xOR orientifold with discrete torsion. The number of independent background lattices is reduced from six to two by new symmetries. The occurrence of USp(2N) and SO(2N) versus U(N) gauge groups is classified as well as D-branes without matter in the adjoint and/or symmetric representation. Supersymmetric fractional D6-branes allowing for RR tadpole cancellation are fully classified in terms of all possible values of the one complex structure modulus inherited from the underlying six-torus. We then systematically investigate the conditions for three particle gene…