Stability of Tripartite Entangled State in Spin Trimer Coupled to a Magnetic Ion

Abstract A model of a spin-1/2 trimer coupled to a magnetic ion with spins ranging from 1/2 to 5/2 is introduced. We numerically calculate tripartite negativity of spin trimer. Numerical results show that the tripartite negativity has a nonzero plateau regardless of spin of the magnetic ion. We focus on tripartite entangled state corresponding to this plateau. As spin and exchange coupling of the magnetic ion increase, the tripartite entangled state becomes increasingly stable with respect to changes in external magnetic field and temperature. This phenomenon originates from the fact that internal magnetic field formed by the magnetic ion compensates the external magnetic field applied to spin trimer.