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Spin-1/2 orthogonal-dimer chain composed of regularly alternating Ising and Heisenberg dimers is exactly solved in a presence of the magnetic field by the transfer-matrix method. It is shown that the ground-state phase diagram involves in total six different phases. Besides the ferromagnetic phase with fully polarized spins one encounters the singlet antiferromagnetic and modulated antiferromagnetic phases manifested in zero-temperature magnetization curves as zero magnetization plateau, the frustrated ferrimagnetic and singlet ferrimagnetic phases causing existence of an intermediate one-half magnetization plateau, and finally, the intriguing modulated ferrimagnetic phase with a translationally broken symmetry leading to an unconventional one-quarter magnetization plateau. The quantum character of individual ground states is quantified via the concurrence, which measures a strength of the bipartite entanglement within the pure and mixed states of the Heisenberg dimers at zero as well as nonzero temperatures. The parameter region, where the bipartite entanglement may be in contrast to general expectations reinforced upon increasing of temperature and/or magnetic field, is elucidated. [ABSTRACT FROM AUTHOR]

Magnetic and thermodynamic characteristics of Ising ferrimagnetic core-shell graphene nanoribbon with core spin −2 and shell spin 5/2 were investigated by using the effective field theory with correlations. Some characteristic phenomena have been found in the system. Different saturation magnetization and P-type and Q-type curves were found on the magnetization curves. At low temperature, the magnetization has obvious magnetization platform. Due to the results of exchange coupling, anisotropy and external magnetic field competition, the m 5 -m 7 sublattice magnetization platform presents a concave shape. The results obtained may have potential applications in the design of nanodevices. • Ising model of core-shell structure graphene nanoribbon is suggested. • Magnetic properties of the system have been studied. • Spin-flip or spin-flop has been found on the magnetization curves. [ABSTRACT FROM AUTHOR]