  As a novel type of fermionic state, hybrid nodal loop with the coexistence of
both type-I and type- II band crossings has attracted intense research
interest. However, it remains a challenge to realize hybrid nodal loop in both
two-dimensional (2D) materials and in ferromagnetic (FM) materials. Here, we
propose the first FM hybrid nodal loop in 2D CrN monolayer. We show that the
material has a high Curie temperature (> 600 K) FM ground state, with the
out-of-plane [001] magnetization. It shows a half-metallic band structure with
two bands in the spin-up channel crossing each other near the Fermi level.
These bands produce both type-I and type-II band crossings, which form a fully
spin-polarized hybrid nodal loop. We find the nodal loop is protected by the
mirror symmetry and robust against spin-orbit coupling (SOC). An effective
Hamiltonian characterizing the hybrid nodal loop is established. We further
find the configuration of nodal loop can be shifted under external
perturbations such as strain. Most remarkably, we demonstrate that both type-I
and type-II Weyl nodes can be realized from such FM hybrid nodal loop by simply
shifting the magnetization from out-of-plane to in-plane. Our work provides an
excellent candidate to realize FM hybrid nodal loop and Weyl fermions in 2D
material, and is also promising for related topological applications with their
intriguing properties.
