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

  Description: 

   This mumax3 script computes the threshold current to get a
   skyrmion through a VCMA gate.

   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)

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

// Set the grid properties
setgridsize(128,64,1)
setcellsize(1e-9,1e-9,1e-9) 
setpbc(4,0,0)

// Given material parameters
Msat  = 580e3
Aex   = 15e-12
Dind  = 3.0e-3
Ku1   = 0.8e6
AnisU = vector(0,0,1)
alpha = 0.1
Pol   = 0.4
xi    = 0.2

// Relax a skyrmion and save this state (we will need this later)
m = neelskyrmion(-1, 1).transl(-40e-9,0,0)
minimize()
saveas(m,"../m0")
flush()

// Switch on the VCMA in the center (5% increase of Ku1)
defRegion(1,rect(50e-9,inf))
Ku1.setRegion(1, 1.05*Ku1.GetRegion(0))

cutofftime := 1e-8

// Start with a high current density for which the skyrmion will get through the gate
// Restart with a slightly lower current density until the skyrmion does not get through

for jx:=2e12; jx>0; jx-=1e11 {

    j = vector(-jx,0,0)
    print("Set current density:", jx, "A/m2")
    
    m.loadfile("m0.ovf")  // reset m to the initial state
    t = 0                 // reset the time

    // run until skyrmion passes x=0 or time exceeds the cut-off time
    runwhile( ext_bubblepos.Get().X()<0 && t<cutofftime)
    
    // check if the skyrmion passed x=0
    if (ext_bubblepos.Get().X() > 0 ) {
        print("Skyrmion got through after", t*1e9 ,"ns")
    } else {
        print("Skyrmion didn't get through!")
        exit()
    }

    // adjust cut-off time
    cutofftime = 2*t
}