/*****************************************************************  

  Description: 

   This mumax3 script demonstartes how skyrmions move in a 
   synthetic antiferromagnet consisting of 2 layers, including
   a spacer layer

   This file is written for the mumax3 workshop organised for the 
   spintronic seminar series in the summer of 2020. For more 
   information go to https://www.mumax.ugent.be/mumax3-workshop
  
  Authors:

   Dr. Jonathan Leliaert (jonathan.leliaert@ugent.be)
   Dr. Jeroen Mulkers    (jeroen.mulkers@ugent.be)

******************************************************************/

// Skyrmion racetrack 


setgridsize(256,64,3)
setcellsize(1e-9,1e-9,1e-9) 
setpbc(4,0,0)
    
Msat = 580e3
Aex = 15e-12
Dind = 3.0e-3
Ku1 = 0.8e6
AnisU = vector(0,0,1)
alpha = 0.1


//Custom Fields implementation for exchange between the 2 FM layers 

cellsize:=1e-9
AFMAex:=-5e-13
Ms:=580e3
prefactorZ := Const( (2 * AFMAex) / (cellsize*cellsize*Ms))

up :=         Mul(prefactorZ,Mul(Add(Mul(Const(-1),m),Shifted(m,0,0, 2)),Shifted(Const(1),0,0,2)))
down :=       Mul(prefactorZ,Mul(Add(Mul(Const(-1),m),Shifted(m,0,0,-2)),Shifted(Const(1),0,0,-2)))

Bc :=Add(up,down)

AddFieldTerm(Bc)
addEdensTerm(Mul(Const(-0.5),Dot(Bc,M_full)))

freelayerthickness=2e-9

// define 2 layers
defregion(1,layer(2))
defregion(2,layer(0))

setgeom(layer(0).add(layer(2)))

//define initial magnetization
m.setregion(1,neelskyrmion(-1, 1).transl(-40e-9,0,0))
m.setregion(2,neelskyrmion(1, -1).transl(-40e-9,0,0))

Minimize()

// define constants and set slonczewksi parameters
SOTxi        := -2
AlphaH       := 0.15
Pol           = alphaH
Lambda        = 1
Epsilonprime  = alphaH*SOTxi/2
Fixedlayer    = vector(0,-1,0)

// define current
J  = vector(0,0,2e11)

autosave(m,1e-10)
tableAutosave(1e-11)
tableAdd(ext_bubblepos)
    
run(2e-9)