Micromagnetics

README.md

@@ -83,7 +83,8 @@ control of parameters.
 
 ### *Physics Features*
 
-- Atomistic Spin Lattice Heisenberg Model including also DMI and dipole-dipole
+- Atomistic spin lattice Heisenberg model including DMI and dipole-dipole interaction
+- Micromagnetic model including DM and dipolar interactions
 - **Spin Dynamics simulations** obeying the
   [Landau-Lifschitz-Gilbert equation](https://en.wikipedia.org/wiki/Landau%E2%80%93Lifshitz%E2%80%93Gilbert_equation)
 - Direct **Energy minimisation** with different solvers

core/README.md

@@ -4,7 +4,7 @@ Spirit
 This is the core library of the **Spirit** framework.
 
 It is meant to provide useful and easy API functions to enable productive work
-with Atomistic Dynamics Simulations and Optimizations.
+with Atomistic and Micromagnetic Dynamics Simulations and Optimizations.
 The current implementation is specific to atomistic spin models, but it may
 easily be generalised.
 

core/docs/Input.md

@@ -6,11 +6,12 @@ The following sections will list and explain the input file keywords.
 1. [General Settings and Log](#General)
 2. [Geometry](#Geometry)
 3. [Heisenberg Hamiltonian](#Heisenberg)
-4. [Gaussian Hamiltonian](#Gaussian)
-5. [Method Output](#MethodOutput)
-6. [Method Parameters](#MethodParameters)
-7. [Pinning](#Pinning)
-8. [Disorder and Defects](#Defects)
+4. [Micromagnetic Hamiltonian](#Micromagnetic)
+5. [Gaussian Hamiltonian](#Gaussian)
+6. [Method Output](#MethodOutput)
+7. [Method Parameters](#MethodParameters)
+8. [Pinning](#Pinning)
+9. [Disorder and Defects](#Defects)
 
 
 General Settings and Log <a name="General"></a>
@@ -169,7 +170,7 @@ For more details, such as the notation used here, see [Phys. Rev. B **99** 22441
 **General Parameters:**
 
 ```Python
-### Hamiltonian Type (heisenberg_neighbours, heisenberg_pairs, gaussian)
+### Hamiltonian Type (heisenberg_neighbours, heisenberg_pairs, micromagnetic, gaussian)
 hamiltonian              heisenberg_neighbours
 
 ### Boundary conditions (in a b c) = 0(open), 1(periodical)
@@ -306,6 +307,80 @@ Pairwise interactions are specified in meV per unique pair \<ij\>,
 while quadruplets are specified in meV per unique quadruplet \<ijkl\>.
 
 
+Micromagnetic Hamiltonian <a name="Micromagnetic"></a>
+--------------------------------------------------
+
+To use a micromagnetic Hamiltonian, use `micromagnetic` as input parameter after the `hamiltonian` keyword.
+
+Note that Spirit only supports rectilinear geometries when using this Hamiltonian.
+
+**Units:**
+
+In the micromagnetic model, Spirit uses SI units:
+- `m` (meter) for distances
+- `J` (Joule) for energies
+- `s` (second) for time
+
+Therefore,
+- `A [J/m]` for exchange stiffness
+- `D [J/m^2]` for DMI
+- `K [J/m^3]` for anisotropy
+- `Ms [A/m]` for saturation magnetisation
+
+**General Parameters:**
+
+```Python
+### boundary_conditions (in a b c) = 0(open), 1(periodical)
+boundary_conditions 0 0 0
+
+### The order of the finite difference approximation of the spatial gradient
+spatial_gradient_order 2
+```
+
+**Static:**
+
+```Python
+# Saturation magnetisation [A/m]
+Ms 1.3e6
+```
+while the magnetocrystalline anisotropy can be specified as an axis,
+```Python
+# Anisotropy [J/m^3]
+anisotropy 0.3e6
+```
+or as a tensor
+```Python
+# Anisotropy [J/m^3]
+tensor_anisotropy
+0.3e6   0       0
+0       0.3e6   0
+0       0       0.3e6
+```
+
+**Interactions:**
+
+The exchange interaction and DMI can each be set either as a constant,
+```Python
+# Stiffness [J/m]
+exchange 10e-12
+# DMI [J/m^2]
+dmi 6e-3
+```
+or as a tensor,
+```Python
+# Stiffness [J/m]
+tensor_exchange
+10e-12   0       0
+ 0      10e-12   0
+ 0       0      10e-12
+# DMI [J/m^2]
+tensor_dmi
+ 0      -6e-3    6e-3
+ 6e-3    0      -6e-3
+-6e-3    6e-3    0
+```
+
+
 Gaussian Hamiltonian <a name="Gaussian"></a>
 ----------------------------------------------------
 

core/include/Spirit/Constants.h

@@ -28,17 +28,26 @@ PREFIX scalar Constants_k_B() SUFFIX;
 // Planck constant [meV*ps / rad]
 PREFIX scalar Constants_hbar() SUFFIX;
 
-// Millirydberg [mRy / meV]
-PREFIX scalar Constants_mRy() SUFFIX;
-
 // Gyromagnetic ratio of electron [rad / (s*T)]
 PREFIX scalar Constants_gamma() SUFFIX;
 
 // Electron g-factor [unitless]
 PREFIX scalar Constants_g_e() SUFFIX;
 
+// Millirydberg [mRy / meV]
+PREFIX scalar Constants_mRy() SUFFIX;
+
+// Erg [erg / meV]
+PREFIX scalar Constants_erg() SUFFIX;
+
+// Joule [J / meV]
+PREFIX scalar Constants_Joule() SUFFIX;
+
 // Pi [rad]
 PREFIX scalar Constants_Pi() SUFFIX;
 
+// Pi/2 [rad]
+PREFIX scalar Constants_Pi_2() SUFFIX;
+
 #include "DLL_Undefine_Export.h"
 #endif

core/include/Spirit/Hamiltonian.h

@@ -56,11 +56,33 @@ Dipole-Dipole method
 #define SPIRIT_DDI_METHOD_CUTOFF 3
 
 
+/*
+Definition of Hamiltonian types
+--------------------------------------------------------------------
+*/
+
+typedef enum
+{
+    Hamiltonian_Heisenberg    = 0,
+    Hamiltonian_Micromagnetic = 1,
+    Hamiltonian_Gaussian      = 2
+} Hamiltonian_Type;
+
 /*
 Setters
 --------------------------------------------------------------------
 */
 
+/*
+Set the kind of Hamiltonian to be used by all systems.
+Can be (case is ignored):
+
+- Heisenberg
+- Micromagnetic
+- Gaussian
+*/
+PREFIX void Hamiltonian_Set_Kind(State *state, Hamiltonian_Type type, int idx_chain=-1) SUFFIX;
+
 // Set the boundary conditions along the translation directions [a, b, c]
 PREFIX void Hamiltonian_Set_Boundary_Conditions(State *state, const bool* periodical, int idx_image=-1, int idx_chain=-1) SUFFIX;
 

core/include/data/Geometry.hpp

@@ -140,10 +140,17 @@ class Geometry
     // Dimensionality of the points
     int dimensionality;
     int dimensionality_basis;
-    // Center and Bounds
+    // Center and bounds [Å]
     Vector3 center, bounds_min, bounds_max;
-    // Unit Cell Bounds
+    // Unit cell bounds [Å]
     Vector3 cell_bounds_min, cell_bounds_max;
+    // Unit cell size [m]
+    Vector3 cell_size;
+    // Unit cell volume [m^3]
+    scalar cell_volume;
+    // Computes the saturation magnetisation density [A/m] 
+    // from the atomistic basis cell composition
+    scalar getMs();
 
 private:
     // Generate the full set of spin positions

core/include/engine/CMakeLists.txt

@@ -3,6 +3,7 @@ set(HEADER_SPIRIT_ENGINE
     ${CMAKE_CURRENT_SOURCE_DIR}/Neighbours.hpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Hamiltonian.hpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Hamiltonian_Heisenberg.hpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/Hamiltonian_Micromagnetic.hpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Hamiltonian_Gaussian.hpp
     ${CMAKE_CURRENT_SOURCE_DIR}/Eigenmodes.hpp
     ${CMAKE_CURRENT_SOURCE_DIR}/HTST.hpp