  Most quantum entanglement investigations are focused on two qubits or some
finite (small) chain structure, since the infinite chain structure is a
considerably cumbersome task. Therefore, the quantum entanglement properties
involving an infinite chain structure is quite important, not only because the
mathematical calculation is cumbersome but also because real materials are well
represented by an infinite chain. Thus, in this paper we consider an entangled
diamond chain with Ising and anisotropic Heisenberg (Ising-XXZ) coupling. Two
interstitial particles are coupled through Heisenberg coupling or simply
two-qubit Heisenberg, which could be responsible for the emergence of
entanglement. These two-qubit Heisenberg operators are interacted with two
nodal Ising spins. An infinite diamond chain is organized by
interstitial-interstitial and nodal-interstitial (dimer-monomer) site
couplings. We are able to get the thermal average of the two-qubit operator,
called the reduced two-qubit density operator. Since these density operators
are spatially separated, we could obtain the concurrence (entanglement)
directly in the thermodynamic limit. The thermal entanglement (concurrence) is
constructed for different values of the anisotropic Heisenberg parameter,
magnetic field and temperature. We also observed the threshold temperature via
the parameter of anisotropy, Heisenberg and Ising interaction, external
magnetic field, and temperature.
