#include <config/config.hpp>
#include "magnetostatics/stoner_wohlfarth_thermal.hpp"
#include "cell_system/CellStructure.hpp"
#include "cells.hpp"
#include "constraints/Constraints.hpp"
#include "constraints/HomogeneousMagneticField.hpp"
#include "errorhandling.hpp"
#include "random.hpp"
#include "rotation.hpp"
#include "thermostat.hpp"
#include "virtual_sites/relative.hpp"
#include <nlopt.hpp>
#include <cassert>
#include <cmath>
#include <numbers>
#include <tuple>
#include <utility>
#include <vector>

Include dependency graph for stoner_wohlfarth_thermal.cpp:

Functions
static double	phi_objective (unsigned n, const double x, double grad, void *my_func_data)
	Objective (energy) function for the Stoner-Wohlfarth phi minimisation.

static double	get_phi_at_energy_min (double theta, double h, double phi0, double ani_param, double tau0_inv, double dt, double const &noise)
	Find the in-plane angle phi corresponding to the correct energy minimum for the thermal Stoner-Wohlfarth particles.

static auto	get_external_field ()
	Collect external homogeneous magnetic field from active constraints.

void	stoner_wohlfarth_no_field (Particle &p, Utils::Vector3d const &e_k, double const kT, double const noise)
	Simplified Stoner-Wohlfarth update in field-free case.

static void	stoner_wohlfarth_main (Particle &p, Utils::Vector3d const &e_k, Utils::Vector3d const &ext_fld_dpl, double const kT, double const noise)
	Update virtual site dipole moment according to the full in-field (incl.

void	run_magnetodynamics (CellStructure &cell_structure, Thermostat::Thermostat const &thermostat)
	Run magnetodynamics update for local virtual particles.

Variables
static constexpr double	eps_phi = 1e-3

static constexpr double	eps_abs = 1e-15

static constexpr double	eps_rel = 1e-15

Function Documentation

◆ get_external_field()

static auto get_external_field ( )

static

Collect external homogeneous magnetic field from active constraints.

Iterate over constraints and sum the homogeneous magnetic field vectors provided by Constraints::HomogeneousMagneticField objects.

Returns: The total external homogeneous magnetic field.

Definition at line 156 of file stoner_wohlfarth_thermal.cpp.

References System::get_system(), and stream.

Referenced by run_magnetodynamics().

◆ get_phi_at_energy_min()

static double get_phi_at_energy_min	(	double	theta,
		double	h,
		double	phi0,
		double	ani_param,
		double	tau0_inv,
		double	dt,
		double const &	noise
	)

static

Find the in-plane angle phi corresponding to the correct energy minimum for the thermal Stoner-Wohlfarth particles.

Parameters

theta	Angle between anisotropy director and external field (rad).
h	Reduced field (external + dipolar) normalised by H_k.
phi0	Initial in-plane angle guess (rad).
ani_param	Inverse thermal energy factor ( \(1/(k_B T V)\) scaled).
tau0_inv	Attempt frequency inverse (1/tau0).
dt	Time increment for switching probability.
noise	Uniform random number in (0,1) used for the kinetic MC step.

Returns: In-plane angle phi in range \( [0,2\pi) \).

Definition at line 91 of file stoner_wohlfarth_thermal.cpp.

References eps_abs, eps_phi, eps_rel, params, phi_objective(), and stream.

Referenced by stoner_wohlfarth_main().

◆ phi_objective()

static double phi_objective	(	unsigned	n,
		const double *	x,
		double *	grad,
		void *	my_func_data
	)

static

Objective (energy) function for the Stoner-Wohlfarth phi minimisation.

Evaluate the magnetic energy (normalized by the anisotropy field) for a given in-plane angle phi according to Eq. 5 in [32]. Assumes minima lie in the plane phi = zeta and uses trig identities to reduce the expression.

Parameters

n	Number of optimization variables (should be 1: phi).
x	Pointer to variables; x[0] is the angle phi.
grad	If non-null, gradient is written to grad[0].
my_func_data	Pointer to a double[2] array with {theta, h}.

Returns: Energy value for the given phi.

Definition at line 66 of file stoner_wohlfarth_thermal.cpp.

References params, and stream.

Referenced by get_phi_at_energy_min().

◆ run_magnetodynamics()

void run_magnetodynamics	(	CellStructure &	cell_structure,
		Thermostat::Thermostat const &	thermostat
	)

Run magnetodynamics update for local virtual particles.

Iterate over local particles and update the dipole moment of virtual particles according to the thermal Stoner-Wohlfarth model. Collect active homogeneous external magnetic fields from constraints and add the per-particle dipolar contribution before performing either the simplified no-field update or the full thermal Stoner-Wohlfarth update.

Parameters

cell_structure	CellStructure providing access to local particles.
thermostat	thermostat used to access Philox RNG state and seeds.

Definition at line 258 of file stoner_wohlfarth_thermal.cpp.

References Particle::dip_fld(), CellStructure::for_each_local_particle(), get_external_field(), get_reference_particle(), Particle::id(), Particle::is_virtual(), Thermostat::Thermostat::kT, Thermostat::Thermostat::langevin, Particle::stoner_wohlfarth_is_enabled(), stoner_wohlfarth_main(), stoner_wohlfarth_no_field(), stream, THERMO_LANGEVIN, Thermostat::Thermostat::thermo_switch, and Utils::uniform().

Referenced by System::System::integrate().

◆ stoner_wohlfarth_main()

static void stoner_wohlfarth_main	(	Particle &	p,
		Utils::Vector3d const &	e_k,
		Utils::Vector3d const &	ext_fld_dpl,
		double const	kT,
		double const	noise
	)

static

Update virtual site dipole moment according to the full in-field (incl.

dipole field) thermal Stoner-Wohlfarth model (incl. the kinetic MC step)

Parameters

[in,out]	p	Virtual particle to update (modified).
	e_k	Anisotropy director of the reference particle.
	ext_fld_dpl	External homogeneous magnetic field + total dipolar field acting on the particle.
	kT	Thermal energy from thermostat.
	noise	Uniform random number in (0,1) used for the kinetic MC step.

Definition at line 216 of file stoner_wohlfarth_thermal.cpp.

References convert_dip_to_quat(), Particle::dipm(), get_phi_at_energy_min(), Particle::magnetic_anisotropy_energy(), Particle::magnetic_anisotropy_field_inv(), Particle::quat(), Particle::saturation_magnetization(), Particle::stoner_wohlfarth_dt_incr(), Particle::stoner_wohlfarth_phi_0(), Particle::stoner_wohlfarth_tau0_inv(), stream, and vector_product().

Referenced by run_magnetodynamics().

◆ stoner_wohlfarth_no_field()

void stoner_wohlfarth_no_field	(	Particle &	p,
		Utils::Vector3d const &	e_k,
		double const	kT,
		double const	noise
	)

Simplified Stoner-Wohlfarth update in field-free case.

Parameters

[in,out]	p	Virtual particle to update.
	e_k	Anisotropy director of the reference particle.
	kT	Thermal energy from thermostat.
	noise	Uniform random number in (0,1) used for the kinetic MC step.

Definition at line 177 of file stoner_wohlfarth_thermal.cpp.

References convert_dip_to_quat(), Particle::dipm(), Particle::magnetic_anisotropy_energy(), Particle::quat(), Particle::saturation_magnetization(), Particle::stoner_wohlfarth_dt_incr(), Particle::stoner_wohlfarth_phi_0(), Particle::stoner_wohlfarth_tau0_inv(), and stream.

Referenced by run_magnetodynamics().