  Searching for room temperature ferromagnetic semiconductors has evolved into
a broad field of material science and spintronics for decades, nevertheless,
these novel states remain rare. Phosphorene, a monolayer black phosphorus with
a puckered honeycomb lattice structure possessing a finite band gap and high
carrier mobility, has been synthesized recently. Here we show, by means of two
different large scale quantum Monte-Carlo methods, that relatively weak
interactions can lead to remarkable edge magnetism in the phosphorene
nanoribbons. The ground state constrained path quantum Monte-Carlo simulations
reveal strong ferromagnetic correlations along the zigzag edges, and the finite
temperature determinant quantum Monte-Carlo calculations show a high Curie
temperature up to room temperature.
