Hysteresis loop for Barium Ferrite

[raghav posti]

Hello,

As a beginner to the mumax i wanted to reproduce a paper, which is related to simulation of Barium Ferrite hysteresis loop for single domain structure, and they have done this simulation on oommf.

When i tried to reproduce the same results using Mumax i got results which are completely different from paper. 

*********************************************************************************

//Script that I've used

SetGridsize(20, 20, 1)  

SetCellsize(2.5e-9, 2.5e-9, 5e-9)

SetGeom(cylinder(50e-9, 5e-9))   // similar results for cylindrical and hexagonal geometry, according to their earlier study(ref.17 of paper attached)

Msat = 275e3

Aex = 2e-11

alpha = 0.1

anisU = vector(0,0,1)

Ku1 = 96e3

m = RandomMag()

relax()

Bmax := 1000e-3

Bstep := 10e-3

MinimizerStop = 1e-6

TableAdd(B_ext)

for B:=Bmax;B>=-Bmax;B-=Bstep{B_ext=vector(0,0,B);minimize();tablesave()}

for B:=-Bmax;B<=Bmax;B+=Bstep{B_ext=vector(0,0,B);minimize();tablesave()}

*********************************************************************************************

I was hoping for a rectangular hysteresis curve, since Barium Farrite have a perpendicular uni-axial anisotropy.

Attached below is the paper that i am following and screenshot of main part that i want to simulate.

[Jeroen Mulkers]

The magnetization state does not change due to the symmetry of the problem. Try to cant the applied magnetization field a little bit to trigger an (artificial) spontaneous symmetry breaking. E.g.

B_ext=vector(0.01*B, 0, B)

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[raghav posti]

Thank you for your help. It works now.

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[raghav posti]

Hi, 

 Can somebody emphasis a little more about the symmetry that was earlier making problem in my simulation?

I want to understand that what type of symmetry it was and how it is broken now, by changing field direction a little from anisotropy direction?

Thanks in advance,

Regards,

Raghav Posti

[Felipe Garcia]

Dear Raghav,

As I have mentioned in other questions, this is due to the fact that you are applying along a direction which is symmetric and the net torque is zero, the state is stationary and unstable but will not switch. This is equivalent to a rock on the top of a mountain, ideally it will not fall unless one produces a shift. To do this, one can do like Jeroen Mulkers proposed, to apply the field with a very small angle or add some noise before each step.

Best regards,

Felipe

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[Nishtha Vats (P19PH016)]

Dear Raghav,

This paper would be of interest to me as well. I would like to know, do you get the same coercivity as discussed in this paper or something different after using B_ext=vector(0.01*B, 0, B)? As I am getting a difference of 40-80 mT rather than the same one.

Best regards,

Nishtha Vats