Проявление фрустраций основного состояния двумерной разбавленной модели Изинга в магнитокалорическом эффекте

The magnetocaloric effect is considered in the 2D dilute Ising model for various ratios of the parameters of inter-site repulsion of nonmagnetic impurities and exchange interaction. Numerical simulations using the classical Monte Carlo method on a square lattice shows that in the case of weak exchange at sufficiently high concentrations of nonmagnetic impurities, long-range ferromagnetic ordering is destroyed with the formation of isolated spin clusters in the ground state of the system. This leads to the appearance of a paramagnetic response of the system at zero temperature and a nonzero entropy of the ground state. In the paper, we discuss the possibility of detecting the frustration of the ground state using data on changes in magnetic entropy.

Exotic criticality in the dimerized spin-1 $XXZ$ chain with single-ion anisotropy

We consider the dimerized spin-1 XXZ chain with single-ion anisotropy D. In absence of an explicit dimerization there are three phases: a large-$D$, an antiferromagnetically ordered and a Haldane phase. This phase structure persists up to a critical dimerization, above which the Haldane phase disappears. We show that for weak dimerization the phases are separated by Gaussian and Ising quantum phase transitions. One of the Ising transitions terminates in a critical point in the universality class of the dilute Ising model. We comment on the relevance of our results to experiments on quasi-one-dimensional anisotropic spin-1 quantum magnets.