Nonlinear optical probe of interface ferromagnetism of EuS-Bi$_{2}$Se$_{3}$ heterostructures

EuS-Bi$_{2}$Se$_{3}$ heterostructure is a novel magnetic topological insulator system with canted ferromagnetism induced at the interface between EuS and Bi$_{2}$Se$_{3.}$ Here we use magnetic second harmonic generation (MSHG) to probe interface ferromagnetism of EuS-Bi$_{2}$Se$_{3}$ heterostructures. MSHG is a powerful nonlinear optical technique that selectively probes magnetism at the surfaces and interfaces of a centrosymmetric material. In order to study how the thickness of the magnetic EuS layer affects interface ferromagnetism, we have grown EuS-Bi$_{2}$Se$_{3}$ heterostructures with varying EuS thicknesses. We have also grown heterostructures in which the EuS thickness increases linearly across a single sample. We discuss how the magnetic layer thickness affects the strength and canting angle of interface magnetism.