Basics

[Shabeer ali pc]

Hi all,

How can i write the appropriate values for 

a)material[1]:exchange-matrix[1]

b)material[1]:atomic-spin-moment=1.32356 !muB  and

c)material[1]:uniaxial-anisotropy-constant=1.0e-26 

for the vampire mat file generation.Is this from DFT calculation,then how can i pick these values(I am using Wien2k for DFT calculations)

I have given an example of mat file below

#---------------------------------------------------
material:num-materials=4
#---------------------------------------------------
material[1]:material-name=Fe
material[1]:unit-cell-category=4
material[1]:damping-constant=1
material[1]:density=1
material[1]:exchange-matrix[1]=11.2e-22
material[1]:exchange-matrix[2]=11.2e-22
material[1]:exchange-matrix[3]=1.25e-21
material[1]:atomic-spin-moment=1.32356 !muB
material[1]:uniaxial-anisotropy-constant=1.0e-26
material[1]:material-element=Fe
#----------------------------------------------------
 

Thanks and regards

SHABEER ALI PC   

Senior Research Fellow 

Functional Materials, Center for Sustainable Energy Technology Division, 

CSIR – National Institute for Interdisciplinary Science and Technology (NIIST) Thiruvananthapuram- 695 019 Kerala, India.   

Mob:+91 8089493635

[gabo...@gmail.com]

a) WIEN2k does not directly output Jij values.  They can be post calculated in some cases but that can sometimes be challenging.  The article at [1] is for Quantum Espresso, but the section "APPENDIX: DETERMINATION OF J1 AND J2" seems to have a good explanation of the method.  This should also be possible with WIEN2k, see slides 54 - 77 in [2].  It is noted, though, that some researchers are using a different DFT program called TB2J since it generates input files for VAMPIRE [3].

b) I've not tried it, but you might be able to use the spin moment inside the sphere (MMI) [4-5].

c) If your crystal structure has uniaxial anisotropy, equation (10) in [6] might be of interest to you.  Their are crystals, however, with different kinds of magnetocrytalline anisotropy such as cubic and triaxial [7].  Torque Magnetometer measurement might be one method for obtaining the anisotropy value, refer to [8].

[1] https://arxiv.org/abs/0804.3370v3

[2] http://www.wien2k.at/events/ws24/Rocquefelte-relativity.pdf

[3] https://tb2j.readthedocs.io/en/latest/src/multibinit.html#interface-with-vampire

[4] https://www.mail-archive.com/wi...@zeus.theochem.tuwien.ac.at/msg19914.html

[5] https://www.mail-archive.com/wi...@zeus.theochem.tuwien.ac.at/msg11651.html

[6] https://dx.doi.org/10.1088/0953-8984/26/10/103202

[7] https://en.wikipedia.org/wiki/Magnetic_anisotropy#Single-domain_magnet

[8] https://www.lakeshore.com/docs/default-source/product-downloads/application-notes/magnetic-anisotropy.pdf

Kind Regards,

Gavin

VAMPIRE user