  We theoretically investigate the dynamics of two spin qubits interacting with
a magnetic medium. A systematic formal framework for this qubit-magnet hybrid
system is developed in terms of the steady-state properties of the magnetic
medium. Focusing on the induced dissipative coupling between the spin qubits,
we show how a sizable long-lived entanglement can be established via the
magnetic environment, in the absence of any coherent coupling. Moreover, we
demonstrate that maximally-entangled two-qubit states (Bell states) can be
achieved in this scheme when complemented by proper postselection. In this
situation, the time evolution of the entanglement is governed by a
non-Hermitian Hamiltonian, where dynamical phases are separated by an
exceptional point. The resultant Bell state is robust against weak random
perturbations and does not require the preparation of a particular initial
state. Our study may find applications in quantum information science, quantum
spintronics, and for sensing of nonlocal quantum correlations.
