A central goal of modern condensed matter physics is to control magnetism at the nanoscale. Recently, a breakthrough platform for exploring this frontier has been brought by semiconducting moiré materials (SMMs) consisting of twisted or lattice-mismatched monolayers of van der Waals (vdW) crystals. With their flat electronic bands and excellent optical properties, SMMs embedded in gated heterostructures host a variety of collective spin phases, thus serving as artificial quantum materials that provide direct optical access to spin-physics and offer a tunability approaching that of cold-atom simulators.