69 lines
3.0 KiB
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69 lines
3.0 KiB
ReStructuredText
Magnetic spins
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==============
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The magnetic spin simulations are enabled by the SPIN package, whose
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implementation is detailed in :ref:`Tranchida <Tranchida>`.
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The model represents the simulation of atomic magnetic spins coupled
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to lattice vibrations. The dynamics of those magnetic spins can be used
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to simulate a broad range a phenomena related to magneto-elasticity, or
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or to study the influence of defects on the magnetic properties of
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materials.
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The magnetic spins are interacting with each others and with the
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lattice via pair interactions. Typically, the magnetic exchange
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interaction can be defined using the
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:doc:`pair/spin/exchange <pair_spin_exchange>` command. This exchange
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applies a magnetic torque to a given spin, considering the orientation
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of its neighboring spins and their relative distances.
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It also applies a force on the atoms as a function of the spin
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orientations and their associated inter-atomic distances.
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The command :doc:`fix precession/spin <fix_precession_spin>` allows to
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apply a constant magnetic torque on all the spins in the system. This
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torque can be an external magnetic field (Zeeman interaction), and an
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uniaxial or cubic magnetic anisotropy.
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A Langevin thermostat can be applied to those magnetic spins using
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:doc:`fix langevin/spin <fix_langevin_spin>`. Typically, this thermostat
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can be coupled to another Langevin thermostat applied to the atoms
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using :doc:`fix langevin <fix_langevin>` in order to simulate
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thermostatted spin-lattice systems.
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The magnetic damping can also be applied
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using :doc:`fix langevin/spin <fix_langevin_spin>`.
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It allows to either dissipate the thermal energy of the Langevin
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thermostat, or to perform a relaxation of the magnetic configuration
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toward an equilibrium state.
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The command :doc:`fix setforce/spin <fix_setforce>` allows to set the
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components of the magnetic precession vectors (while erasing and
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replacing the previously computed magnetic precession vectors on
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the atom).
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This command can be used to freeze the magnetic moment of certain
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atoms in the simulation by zeroing their precession vector.
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The command :doc:`fix nve/spin <fix_nve_spin>` can be used to
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perform a symplectic integration of the combined dynamics of spins
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and atomic motions.
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The minimization style :doc:`min/spin <min_spin>` can be applied
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to the spins to perform a minimization of the spin configuration.
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All the computed magnetic properties can be output by two main
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commands. The first one is :doc:`compute spin <compute_spin>`, that
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enables to evaluate magnetic averaged quantities, such as the total
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magnetization of the system along x, y, or z, the spin temperature, or
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the magnetic energy. The second command
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is :doc:`compute property/atom <compute_property_atom>`.
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It enables to output all the per atom magnetic quantities. Typically,
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the orientation of a given magnetic spin, or the magnetic force
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acting on this spin.
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----------
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.. _Tranchida:
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**(Tranchida)** Tranchida, Plimpton, Thibaudeau and Thompson,
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Journal of Computational Physics, 372, 406-425, (2018).
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