We investigate the magnetocaloric effect in a diamond chain model on which competing interactions result from the local quantum hopping of interstitial S =1/ 2 spins which are intercalated between nodal Ising spins. The model is exactly solvable by using exact diagonalization and the decoration-iteration mapping onto the one-dimensional Ising model with effective parameters depending on the temperature and the external magnetic field. We analyze the thermodynamic behavior of the effective parameters in light of the ground-state ordering and the level crossing of the low-lying excited states. Further, we investigate the magnetocaloric effect on this spin chain model by computing isoentropy curves in the temperature versus external field parameter space, as well as the adiabatic cooling rate. We show that the adiabatic cooling rate exhibits a pronounced valley-peak structure in the vicinity of the critical fields associated with zero-temperature phase transitions.

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The strongly correlated spin-electron system on a diamond chain containing localized Ising spins on its nodal lattice sites and mobile electrons on its interstitial sites is exactly solved in a magnetic field using the transfer-matrix method. We have investigated in detail all available ground states, the magnetization processes, the spin-spin correlation functions around an elementary plaquette, fermionic quantum concurrence and spin frustration. It is shown that the fermionic entanglement between mobile electrons hopping on interstitial sites and the kinetically-induced spin frustration are closely related yet independent phenomena. In the ground state, quantum entanglement only appears within a frustrated unsaturated paramagnetic phase, while thermal fluctuations can promote some degree of quantum entanglement above the non-frustrated ground states with saturated paramagnetic or classical ferrimagnetic spin arrangements.

A large number of interesting phenomena related to the insertion of colloidal particles in liquid crystals (LC) have recently been reported. Here, we investigate effects caused by the addition of spherically shaped ferroelectric nanoparticles to a nematic liquid crystal. Using molecular dynamics (MD) simulations, the density of LC molecules, the orientational order parameter, and the polar and azimuthal angle profiles are calculated as functions of the distance to the center of the immersed nanoparticle for different temperatures of the system. We observe that the assembly of ferroelectric nanoparticles enhances the nematic order in the LC medium changing many properties of its host above the nematic-isotropic transition temperature T (*) (NI) .

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