I have been using the Vampire atomistic simulation software for a while and it has a useful simulation for predicting the curie temperature. But in order to do that I need the exchange matrix of Co-CoO system which should include the constant which represents the interaction between spins in the Co part, spins in the CoO part and a constant representing the interaction of spins in the Co-CoO interface. So I have been able to obtain the values for the Co and CoO part by couldn't find any resources to calculate the term representing the interaction at the interface. Should I use the average of the two values I've obtained. How should I approach this problem?
An excerpt from the VAMPIRE manual regarding this is given below:
material:exchange-matrix[index] = float [default 0.0 J/link] Defines the pair-wise exchange energy between atoms of type index and neighbour-index. The pairwise exchange energy is independent of the coordination number, and so the total exchange integral will depend on the number of nearest neighbours for the crystal lattice. The exchange energy must be defined between all material pairs in the simulation, with positive values representing ferromagnetic coupling, and negative values representing antiferromagnetic coupling. For a ferromagnet with a nearest neighbour exchange, the pairwise exchange energy can be found from the Curie temperature by the mean-field expression:
$$J_{ij} = \frac{(3k_{b}T_{c})}{\epsilon z}$$
where $J_{ij}$ is the exchange energy, $k_{b}$ is the Boltzmann constant, $T_{c}$ is the Curie temperature, z is the coordination number (number of nearest neighbours) and $\epsilon$ is a correction factor to account for spin-wave fluctuations in different crystal lattices. If a custom unit cell file is used the exchange values defined here are ignored.
I have included the manual here in this link. VAMPIRE Manual