Dear Siraj Ulhaq,
I'm working with AFM materials similar to yours, I have not yet worked with Exchange Bias in Vampire (I'll soon do that), but on the vampire site there's an FM / AFM example, just follow the template ... You have to find the atomic-spin-moment of your materials, or you consider them separate or together. To put the other terms of energy follows the attached manual, but it is the same thing:
material: uniaxial-anisotropy-constant = fl oat [default 0.0 J / atom]
material: second-uniaxial-anisotropy-constant = fl oat [default 0.0 J / atom]
material: cubic-anisotropy-constant = fl oat [default 0.0 J / atom]
material: uniaxial-anisotropy-direction = fl oat vector [default (001)]
material: surface-anisotropy-constant = fl oat default 0.0 (J / atom)
material: relative-gamma fl oat [default 1]
material: initial-spin-direction fl oat vector / bool [default (001) / false]
Are you part of ResearchGate? If so, follow my project there ...