Magnetic Excitations and Q-dependent magnon lifetime in Non-collinear Metallic Antiferromagnet CrB₂

Frustration and non-collinear magnetic ordering can introduce a wide variety of interesting physics; like a quantum spin liquid phase in insulators or topological band structures in metals, to name a few. Many studies have been made on the nature of magnetic excitations in non-collinear insulating magnets, while few experimental data exist for non-collinear metallic magnets. Using an inelastic neutron scattering technique, we report the magnetic excitation spectra of single crystal CrB₂; a metallic magnet in which magnetic moments of Cr on triangular lattice form incommensurate spiral magnetic order with the propagation vector k =(0.285,0.285,0). Severely damped magnons are observed along with clear phonons which are as sharp as the instrumental resolution, yet most of them can be explained by Heisenberg Hamiltonian and a linear spin wave theory (LSWT). By excluding the effects of instrumental resolution, we mapped the intrinsic magnon linewidth Γ(q, E) which shows some unusual behavior. We discuss the origin of the magnon decay by calculating 2-magnon density of states (DOS) and Stoner continuum DOS. Our work will be a rare comprehensive study on the spin dynamics of non-collinear metallic magnets; the 1st observation of 2-magnon effect in metallic magnets.