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A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
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The most common application of magnetic force on current-carrying wires is in electric motors. These consist of loops of wire, which are placed between the magnets with a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate, thus converting electrical energy to mechanical energy.
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All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
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Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques
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Quantum rings in magnetic fields and spin current generation.

Michele Cini1, Stefano Bellucci

  • 1Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome, Italy. Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati, Via E. Fermi 40, I-00044 Frascati, Italy.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|March 19, 2014
PubMed
Summary

We present three methods to generate spin-polarized currents in quantum rings using time-dependent magnetic fields. Two methods produce alternating currents without spin-orbit interaction, while the third generates a purely spin current with spin-orbit interaction.

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Area of Science:

  • Quantum physics
  • Condensed matter physics
  • Spintronics

Background:

  • Spin-polarized currents are crucial for spintronics applications.
  • Controlling spin currents in nanoscale devices is a key challenge.
  • Quantum rings offer a platform for studying spin-dependent transport phenomena.

Purpose of the Study:

  • To propose novel mechanisms for pumping spin-polarized currents in a ballistic quantum ring.
  • To investigate the role of time-dependent magnetic fields and spin-orbit interaction in generating spin currents.
  • To analytically and numerically demonstrate the feasibility of these pumping mechanisms.

Main Methods:

  • Theoretical modeling of electron transport in a quantum ring.
  • Application of time-dependent magnetic fields (rotating or in-plane).
  • Analytical derivations and numerical simulations of charge and spin currents.

Main Results:

  • A rotating magnetic field generates an alternating current with partial spin polarization.
  • Rotating the quantum ring in a constant field produces an alternating charge current and a DC spin current.
  • A purely spin current can be pumped using spin-orbit interaction and an in-plane time-dependent magnetic field.

Conclusions:

  • Three distinct mechanisms for pumping spin-polarized currents in quantum rings are demonstrated.
  • The proposed methods offer pathways to generate spin currents with or without spin-orbit interaction.
  • The findings contribute to the development of spin-based electronic devices.