Long-range Magnetic Fields Research Articles

High-sensitivity operation of an unshielded single cell radio-frequency atomic magnetometer

Real-world applications of atomic magnetometers require the ability to operate them with high-sensitivity in the presence of magnetic noise. In the present work, high-sensitivity operation of unshielded atomic magnetometers in a magnetically noisy environment is demonstrated. The distinguishing feature of the demonstrated approach is the implementation of active in-situ bias field stabilization using multiple fluxgate magnetometers. This is combined with the use of a counter-propagating pump and triple-pass probe configuration, to maximize the atomic polarization and the probe rotation respectively, so to reach high-sensitivity. The improvement in sensitivity of the unshielded system with respect to previous realizations is fully characterized, with the contributions of the different modifications of the apparatus individually quantified. The presented set-up is suitable for the detection of long-range magnetic fields, where shielding or differential measurements using multi-sensor set-ups do not constitute viable options.

Quantum theory of magnon excitation by high energy electron beams

The role of magnon inelastic scattering in high energy electron diffraction of spin unpolarised electron beams, including vortex beams, is investigated theoretically for a Heisenberg ferromagnet. The interaction is between the atomic magnetic dipoles in the specimen and orbital angular momentum (OAM) of the electron beam. Magnon inelastic scattering by vortex beams is allowed despite many atoms along the magnon spin wave experiencing mixed OAM states. The scattering cross-section is however independent of the vortex beam winding number. In the case of planes waves in ferromagnetic iron, the magnon diffuse scattered intensity is significantly smaller than phonons in the energy loss range currently accessible by state-of-the-art monochromated electron energy loss spectroscopy (EELS). Nevertheless, it is shown that the long-range magnetic field of the atomic dipoles has a similar role to dipole scattering in phonon excitation. This means that magnons could, in principle, be detected using aloof beam EELS, where long acquisition times can be realised without any specimen beam damage, an important pre-requisite for detecting the weak magnon signal.

Biomineralized iron oxide-polydopamine hybrid nanodots for contrast-enhanced T1-weighted magnetic resonance imaging and photothermal tumor ablation.

Iron oxide nanoparticles (IO NPs) have become the focus of molecular imaging probes for contrast enhanced magnetic resonance (MR) imaging due to their intrinsic magnetic and biodegradable properties, as well as long blood half-lives and low toxicity. Massive efforts have been made to explore the IO NPs as T2-weighted MR contrast agents, which have high susceptibility to induce a long-range magnetic field that interferes with diagnosis. Thus, the development of IO NPs with potent T1 relaxivity might help in providing an alternative for clinically applied gadolinium chelates. Herein, biomineralized iron oxide-polydopamine hybrid nanodots (IO/PDA-NDs) have been constructed using albumin as the nanoreactors to induce nanoprecipitation and polymerization simultaneously, facilitating T1-weighted contrast-enhancement as well as photothermal therapeutic capability. The IO nanoclusters in IO/PDA-NDs have an r1 relaxivity of 5.79 mM-1 s-1 with a relatively low r2/r1 ratio of 1.71, demonstrating the preferable iron oxide based T1 contrast agents. The high photothermal conversion coefficient and tumor targeting effect of the hybrid nanodots could result in complete tumor ablation efficacy. The biomineralization method provides a promising approach for the integration of tumor diagnosis and treatment to achieve efficient cancer theranostics.

Highly parallel demagnetization field calculation using the fast multipole method on tetrahedral meshes with continuous sources

The long-range magnetic field is the most time-consuming part in micromagnetic simulations. Computational improvements can relieve problems related to this bottleneck. This work presents an efficient implementation of the Fast Multipole Method [FMM] for the magnetic scalar potential as used in micromagnetics. The novelty lies in extending FMM to linearly magnetized tetrahedral sources making it interesting also for other areas of computational physics. We treat the near field directly and in use (exact) numerical integration on the multipole expansion in the far field. This approach tackles important issues like the vectorial and continuous nature of the magnetic field. By using FMM the calculations scale linearly in time and memory.

When electric charge becomes also magnetic

In nonlinear electrodynamics, QED included, we find a static solution to the field equations with an electric charge as its source, which is comprised of homogeneous parallel magnetic and electric fields, and a radial spherically-nonsymmetric long-range magnetic field, whose magnetic charge is proportional to the electric charge and also depends on the homogeneous component of the solution.

A stochastic approach to the solution of magnetohydrodynamic equations

The construction of stochastic solutions is a powerful method to obtain localized solutions in configuration or Fourier space and for parallel computation with domain decomposition. Here a stochastic solution is obtained for the magnetohydrodynamics equations. Some details are given concerning the numerical implementation of the solution which is illustrated by an example of generation of long-range magnetic fields by a velocity source.

Observation of Optical Chemical Shift by Precision Nuclear Spin Optical Rotation Measurements and Calculations

Nuclear spin optical rotation (NSOR) is a recently developed technique for detection of nuclear magnetic resonance via rotation of light polarization, instead of the usual long-range magnetic fields. NSOR signals depend on hyperfine interactions with virtual optical excitations, giving new information about the nuclear chemical environment. We use a multipass optical cell to perform the first precision measurements of NSOR signals for a range of organic liquids and find clear distinction between proton signals for different compounds, in agreement with our earlier theoretical predictions. Detailed first-principles quantum mechanical NSOR calculations are found to be in agreement with the measurements.

Long-Range Magnetic Fields in the Ground State of the Standard Model Plasma

In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at nonzero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new equilibrium state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly. This situation could occur in the early Universe and may play an important role in its subsequent evolution.

Spiraling attractors and quantum dynamics for a class of long-range magnetic fields

We consider the long time behavior of a quantum particle in a 2D magnetic field which is homogeneous of degree −1. If the field never vanishes, above a certain energy the associated classical dynamical system has a globally attracting periodic orbit in a reduced phase space. For that energy regime, we construct a simple approximate evolution based on this attractor, and prove that it completely describes the quantum dynamics of our system.

Properties of the interface in the confined Ising magnet with competing surface fields

A two-dimensional magnetic Ising system confined in an L × D geometry ( L ⪡ D ) in the presence of competing magnetic fields ( h) acting at opposite walls along the D -direction, exhibits an interface between domains of different orientation that run parallel to the walls. In the limit L → ∞ , this interface undergoes a wetting transition that occurs at the critical curve T w ( h ) , so that for T < T w ( h ) such an interface is bound to the walls, while for T w ( h ) ⩽ T < T cb the interface is freely fluctuating around the center of the film, where T cb is the bulk critical temperature. By considering both short- and long-range magnetic fields acting at the walls, we study the divergence of the (equilibrated) average position of the interface when approaching the wetting critical point. Furthermore, starting from a monodomain structure with the interface bound to one wall, we also study the dynamics of the interface unbinding.

Study of the dynamic growth of wetting layers in the confined Ising model with competingsurface fields

A two-dimensional magnetic Ising system confined in anL × D geometry () in the presence of competing magnetic fields(h) acting at oppositewalls along the D-direction exhibits an interface between domains of different orientation thatruns parallel to the walls. In the limit of infinite film thickness () this interface undergoes a wetting transition that occurs at the critical curveTw(h), sothat for T<Tw(h) such an interface is bound to the walls, while forTw(h)≤T≤Tcb the interface is freely fluctuating around the centre of the film, whereTcb is the bulk critical temperature. Starting from a monodomain structure with the interfacebound to one wall, we study the onset of the interface unbinding by considering bothshort- and long-range magnetic fields acting at the walls. It is shown that, within the criticalwetting regime, in both cases the correlation length of interfacial fluctuations grows with time t as with z = 2, while the interfacial position follows both in the case of short-range and long-range surface fields, respectively, consistent withdynamic scaling predictions. Furthermore, considering the complete wetting regime and inthe presence of a bulk magnetic field, we find that the interface location also obeysstandard dynamic scaling behaviour for both short-range and long-range fields.

Finite fermion density effects on the electroweak string

We consider an electroweak string in the background of a uniform distribution of cold fermionic matter. As a consequence of the fermion number non-conservation in the Weinberg-Salam model, the string produces a long-range magnetic field.

Short-range scattering in long-range magnetic fields: The relativistic case

We study relativistic scattering theory for the Dirac equation in the presence of a long-range magnetic field B( x) ~ const. (1 + ¦x¦) −3 2 − δ . Making use of the gauge freedom we prove asymptotic completeness for the unmodified Møller operators, although the vector potential decays very slowly. This generalizes a corresponding nonrelativistic result in [5]. The main new problem is to control the effects of “Zitterbewegung”. Our proof also works for Yang-Mills fields.

Normal forms of an abstract Dirac operator and applications to scattering theory

The unitary transformations which convert an abstract Dirac operator into an ‘‘even’’ (resp. ‘‘odd’’) operator are determined. The problem is formulated and solved completely within the general setup of supersymmetric quantum mechanics. This leads to some apparently new applications in relativistic quantum mechanics, where the transformations are known as the Foldy–Wouthuysen (resp. Cini–Touschek) transformations. The scattering theory for abstract Dirac operators is discussed and the utility of the general theory is illustrated by proving existence of relativistic Mo/ller operators for scattering from long-range magnetic fields.

Scattering of particles by long-range magnetic fields: Michael Loss and Bernd Thaller. Institut für Mathematik I, Freie Universität Berlin, D-1000 Berlin 33, West Germany

Scattering of particles by long-range magnetic fields: Michael Loss and Bernd Thaller. Institut für Mathematik I, Freie Universität Berlin, D-1000 Berlin 33, West Germany

Scattering of particles by long-range magnetic fields

The seattering of nonrelativistic particles (either quantum mechanical or classical) by a magnetic field B is studied in any dimension ν ≥ 2. B( x) is allowed to decay like | x| −3.2 · δ (δ > 0), as | x| → ∞. Assumptions are made about the field strengths and not about the potentials. A gauge is constructed for which the unmodified wave operators exist and are complete even though the corresponding classical motion need not be asymptotically free. The result also holds for Yang-Mills fields.