“…The volume exchange stiffness, A , is related to the quantum mechanical exchange stiffness, J , in a cubic system by the relation A = JS 2 / a , where S is the spin of the local moments and a is the lattice parameter. This produces an exchange stiffness constant, A ex , of 1.86 pJ/m, which is in good agreement with the literature, which suggests values between 1.7 and 1.5 pJ/m . Measuring the exchange stiffness is not trivial and is typically done through the excitation of spin waves by light, neutrons, or microwaves .…”