Title: Discontinuous classical ground state magnetic response as an even-odd effect in higher order rotationally invariant exchange interactions,
Abstract: The classical ground state magnetic response of the Heisenberg model when
rotationally invariant exchange interactions of integer order q>1 are added is
found to be discontinuous, even though the interactions lack magnetic
anisotropy. This holds even in the case of bipartite lattices which are not
frustrated, as well as for the frustrated triangular lattice. The total number
of discontinuities is associated with even-odd effects as it depends on the
parity of q via the relative strength of the bilinear and higher order exchange
interactions, and increases with q. These results demonstrate that the precise
form of the microscopic interactions is important for the ground state
magnetization response.