The Distribution of Magnetization for a Stepped Ferro-antiferromagnet Interface

Multilayer systems with alternating layers of ferromagnets (FM) and antiferromagnets (AFM) [1] have been drawing a special attention. In experiments some interlayers are often wedge-shaped with a small divergence angle [2] and the interface has a stepped form with a large separation between steps. The presence of a step at the boundary of a layered AFM leads to local variation of the magnetic structure [3]. We shall show that the presence of an atomic step at the FM-AFM interface leads to the emergence of the magnetic disclination. Let us consider a plane FM-AFM interface with a strong easy-plane anisotropy. All spins are characterized only by their angle in this plane. In the presence of an atomic size step at this boundary, the spin distribution is noncollinear and the system acquires a magnetic disclination having Frank's index k = 1 and its center at a step. We replace an interface with a step by the ideal boundary with the reversed sign of the exchange interaction through it on one of the semi-axes. Let us consider a 2D lattice with the FM-AFM interface along the x-axis, antiferromagnetic ordering along z-direction and the Hamiltonian