Anisotropy tensor

[milton...@gmail.com]

Hello!

I would like to have both easy-plane anisotropy and easy-axis anisotropy with different anisotropy constants. Is this possible?

I saw that in vampire/scr/anisotropy/interface.cpp there is something called "uniaxial-anisotropy-tensor" and "cubic-anisotropy-tensor", but they are commented out. Would they solve my problem if I uncomment them? Are they perhaps available in the developer version? How does one obtain the developer version anyway?

Thanks in advance!
/Milton

[Liza T]

Hello, just wondering, has this been resolved? Would appreciate some pointers on this as well.

Thank you!!

[gabo...@gmail.com]

I would like to have both easy-plane anisotropy and easy-axis anisotropy with different anisotropy constants.

The above seems to saying what is wanted is something like:

material[1]:uniaxial-anisotropy-constant=2e-23
material[1]:uniaxial-anisotropy-direction=0,0,1

material[1]:uniaxial-anisotropy-constant=3e-23
material[1]:uniaxial-anisotropy-direction=0,1,1

First, I suppose you could give the above a try in your input file, but it might just error for example since material[1]:uniaxial-anisotropy-constant is defined twice or the program might just ignore one of the material[1]:uniaxial-anisotropy-constant instances.  If that is the case, it point towards that not being implemented in the VAMPIRE program such that you would have to do your own programming to make that possibly.  Second, I'm not sure if such a case exists in nature.  I think a magnetic region (grain) might be homogeneous having one anisotropy constant but you would have to go consult your magnetics textbooks on that.

Now, if you have two regions (e.g., bilayer), I think you could use:

material[1]:uniaxial-anisotropy-constant=2e-23
material[1]:uniaxial-anisotropy-direction=0,0,1

material[2]:uniaxial-anisotropy-constant=3e-23
material[2]:uniaxial-anisotropy-direction=0,1,1

On the other hand, if are wanting to have one anisotropy constant with two different directions, you could try cubic anisotropy.  I believe for that to work it would be something like:

material[1]:cubic-anisotropy-constant=2e-23
material[1]:cubic-anisotropy-direction-1=0,0,1
material[1]:cubic-anisotropy-direction-2=0,1,1

How does one obtain the developer version anyway?

1. Go to: https://github.com/richard-evans/vampire/branches

2. Under Active branches, click on develop

Note: If it is not displayed, try searching for it with the keyword develop in the "Search branches..." box.

I'm thinking the develop branch is what the developer version is.

Kind Regards,

Gavin

VAMPIRE user

[milton...@gmail.com]

Thank you Gavin!

It's in the developer version and can be done like this:

material[1]:second-order-triaxial-basis-vector-1 = 1,0,0 # for easy-axis
material[1]:second-order-triaxial-basis-vector-2 = 0,1,0 # personally don't use this one
material[1]:second-order-triaxial-basis-vector-3 = 0,0,1 # for easy-plane
material[1]:second-order-triaxial-basis-vector = 5.65e-25, 5.65e-25, -2.00e-23 # constants for the three directions, negative value for easy-plane

The easy-plane anisotropy was just for the shape anisotropy in thin films, because dipole fields are expensive and not always available. Maybe there is some better "demagnetisation field" feature now, I dunno.

[milton...@gmail.com]

Sorry the last line should have "anisotropy" instead of "basis":
material[1]:second-order-triaxial-anisotropy-vector = ...