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Merge pull request #108 from computationalmodelling/extra_dmi_terms
Simplified micro DMI calculation. Added D_2d DMI
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‎fidimag/micro/dmi.py‎

Lines changed: 69 additions & 38 deletions
Original file line numberDiff line numberDiff line change
@@ -39,6 +39,15 @@ class DMI(Energy):
3939
neighbouring sites in the xy plane and not between
4040
layers in the z direction.
4141
42+
D_2d :: The energy density of this DMI is
43+
44+
w = D * ( L_{xz}^{(y)} + L_{yz}^{(x)} )
45+
46+
where L are Lifshitz invariants. This DMI is for
47+
materials with symmetry class D_{2d}. Structures
48+
known as anti-skyrmions are stabilised with this
49+
DMI type
50+
4251
ARGUMENTS: ----------------------------------------------------------------
4352
4453
D :: DMI vector norm which can be specified as an int, float, (X * n)
@@ -55,12 +64,12 @@ class DMI(Energy):
5564
5665
(X * n) array: Manually specify the DMI vector norm for every NN
5766
at every mesh node. The bulk DMI considers the 6 NNs from every
58-
node an interfacial DMI is D so it only considers 4 NNs from the
59-
xy plane.
67+
node and interfacial and D_2d DMI are 2D so they only consider 4
68+
NNs from the xy plane.
6069
6170
OPTIONAL ARGUMENTS: -------------------------------------------------------
6271
63-
dmi_type :: 'bulk' or 'interfacial'
72+
dmi_type :: 'bulk' or 'interfacial' or 'D_2d'
6473
name :: Interaction name
6574
6675
"""
@@ -73,26 +82,37 @@ def __init__(self, D, name='DMI', dmi_type='bulk'):
7382
self.jac = True
7483
self.dmi_type = dmi_type
7584

85+
# Number of NNs for the calculation of the corresponding DMI
86+
# Interfacial or D_2d are 2D so we use 4 ngbs
7687
if self.dmi_type == 'bulk':
77-
self.NN = 6
88+
self.n_dmi_ngbs = 6
7889
elif self.dmi_type == 'interfacial':
79-
self.NN = 4
90+
self.n_dmi_ngbs = 4
91+
elif self.dmi_type == 'D_2d':
92+
self.n_dmi_ngbs = 4
93+
else:
94+
raise Exception(
95+
"Unsupported DMI type: {}, " +
96+
"available options: ".format(self.dmi_type) +
97+
"'bulk', 'interfacial', 'D_2d'."
98+
)
8099

81100
def setup(self, mesh, spin, Ms):
82101
super(DMI, self).setup(mesh, spin, Ms)
83102

84103
# We will allow to completely specify the DMI vectors according to the
85-
# NNs of every lattice site, thus we need a matrix of NN * n entries
86-
self.Ds = np.zeros(self.NN * self.n, dtype=np.float)
104+
# NNs of every lattice site, thus we need a matrix of n_dmi_ngbs * n entries
105+
self.Ds = np.zeros(self.n_dmi_ngbs * self.n, dtype=np.float)
87106

88-
if isinstance(self.D, np.ndarray) and len(self.D) == self.NN * self.n:
107+
if isinstance(self.D, np.ndarray) and len(self.D) == self.n_dmi_ngbs * self.n:
89108
self.Ds = self.D.astype('float')
90-
# If we do not pass a (NN * n) array, we just create a scalar field as
91-
# usual and then repeat the entries NN times so every neighbour will
92-
# have the same DMI per lattice site (can vary spatially)
109+
# If we do not pass a (n_dmi_ngbs * n) array, we just create a scalar
110+
# field as usual and then repeat the entries NN times so every
111+
# neighbour will have the same DMI per lattice site (can vary
112+
# spatially)
93113
else:
94114
D_array = helper.init_scalar(self.D, self.mesh)
95-
self.Ds = np.repeat(D_array, self.NN)
115+
self.Ds = np.repeat(D_array, self.n_dmi_ngbs)
96116

97117
# This is from the original code:
98118
# self.Ds[:] = helper.init_scalar(self.D, self.mesh)
@@ -104,32 +124,43 @@ def compute_field(self, t=0, spin=None):
104124
m = self.spin
105125

106126
if self.dmi_type == 'bulk':
107-
micro_clib.compute_dmi_field_bulk(m,
108-
self.field,
109-
self.energy,
110-
self.Ms_inv,
111-
self.Ds,
112-
self.dx,
113-
self.dy,
114-
self.dz,
115-
self.n,
116-
self.neighbours
117-
)
127+
dmi_vector = np.array([-1., 0, 0,
128+
1., 0, 0,
129+
0, -1., 0,
130+
0, 1., 0,
131+
0, 0, -1.,
132+
0, 0, 1.
133+
])
118134

119135
elif self.dmi_type == 'interfacial':
120-
micro_clib.compute_dmi_field_interfacial(m,
121-
self.field,
122-
self.energy,
123-
self.Ms_inv,
124-
self.Ds,
125-
self.dx,
126-
self.dy,
127-
self.dz,
128-
self.n,
129-
self.neighbours
130-
)
131-
else:
132-
raise Exception(
133-
"Unsupported DMI type: {}, avaiable options: 'bulk', 'interfacial'.".format(self.dmi_type))
134-
136+
dmi_vector = np.array([0, -1., 0, # -x
137+
0, 1., 0, # +x
138+
1., 0, 0, # -y
139+
-1., 0, 0, # +y
140+
0, 0, 0, # -z
141+
0, 0, 0 # +z
142+
])
143+
144+
elif self.dmi_type == 'D_2d':
145+
dmi_vector = np.array([1., 0, 0, # -x
146+
-1., 0, 0, # +x
147+
0, -1., 0, # -y
148+
0, 1., 0, # +y
149+
0, 0, 0, # -z
150+
0, 0, 0 # +z
151+
])
152+
153+
micro_clib.compute_dmi_field(m,
154+
self.field,
155+
self.energy,
156+
self.Ms_inv,
157+
self.Ds,
158+
dmi_vector,
159+
self.n_dmi_ngbs,
160+
self.dx,
161+
self.dy,
162+
self.dz,
163+
self.n,
164+
self.neighbours
165+
)
135166
return self.field

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