A hybrid spin-electron system defined on one-dimensional double-tetrahedral chain, in which the localized Ising spin regularly alternates with two mobile electrons delocalized over a triangular plaquette, is exactly solved with the help of generalized decoration-iteration transformation. It is shown that a macroscopic degeneracy of ferromagnetic and ferrimagnetic ground states arising from chiral degrees of freedom of the mobile electrons cannot be lifted by a magnetic field in contrast to a macroscopic degeneracy of the frustrated ground state, which appears owing to a kinetically-driven frustration of the localized Ising spins. An anomalous behavior of all basic thermodynamic quantities can be observed on account of massive thermal excitations, which mimic a temperature-driven first-order phase transition from the non-degenerate frustrated state to the highly degenerate ferrimagnetic state at non-zero magnetic fields. A substantial difference in the respective degeneracies is responsible for an immense low-temperature peak of the specific heat and very abrupt (almost discontinuous) thermal variations of the entropy and sublattice magnetizations.
The magnetocaloric effect in the symmetric spin-1/2 Ising-Heisenberg diamond chain with the Ising four-spin interaction is investigated using the generalized decoration-iteration mapping transformation and the transfermatrix technique. The entropy and the Grüneisen parameter, which closely relate to the magnetocaloric effect, are exactly calculated to compare the capability of the system to cool in the vicinity of different field-induced ground-state phase transitions during the adiabatic demagnetization.
Phone: + 421 55 602 2228A symmetric spin-1/2 Ising-Heisenberg diamond chain with the Ising four-spin interaction is exactly solved by means of the generalized decoration-iteration mapping transformation. The ground state, the magnetization process and thermodynamics are particularly examined for the case of antiferromagnetic pair interactions (Ising and isotropic Heisenberg ones). It is shown that an interplay between pair interactions, the four-spin interaction and the external magnetic field gives rise to several quantum ground states with entangled spin states in addition to some semi-classically ordered ones. Besides, the temperature dependence of the magnetic susceptibility multiplied by the temperature is studied and the interesting triple-peak specific heat curve is also detected when considering the zero-field region rather close to the triple point, where three different ground states coexist.Copyright line will be provided by the publisher 1 Introduction Spin systems with multispin exchange interactions represent objects of scientific interest in the past few years. Research in this field leads to a deeper understanding of many interesting physical phenomena, such as the non-universal critical behaviour [1,2], optical conductivity [3], Raman peaks [4], as well as, deviations from the Bloch T 3/2 law at low temperatures [5,6]. Moreover, the effect of magnetic field on the ground state of quantum systems with cyclic four-spin interaction has been recently particularly examined as well [7,8,9]. Of course, the immense theoretical interest to the spin models with multispin interactions is not purposeless. Multispin interactions have been experimentally observed in real triangular magnetic systems composed of 3 He atoms absorbed on graphite surfaces [10], the hydrogen bonded ferroelectrics PbHPO 4 and PbDPO 4 [11], as well as, the squaric acid crystal (H 2 C 2 O 4 ) [12,13,14] and some copolymers [15]. Recently, it was shown that the cyclic four-spin interaction could also explain the neutron-scattering experiments concerning high-T c compounds such as La 2 CuO 4 [16], La 6 Ca 8 Cu 24 O 41 [17,18], and La 4 Sr 10 Cu 24 O 41 [19].On the theoretical side, in spite of the numerous numerical studies predicting rich phase diagrams [20,21,22,23], a number of important questions concerning the spin ordering and the critical behaviour of quantum Heisenberg models realized by the four-spin interaction, remain unclear due to controversial results obtained by different treatments [24,25,26,27]. From this point of view, the exactly solvable models play an important role in understanding the multispin effects. Of course, the quantum spin models is very difficult to deal with exactly due to a rather cumbersome and sophisticated mathematics, which precludes an exact treatment of the most (even simpleminded) spin systems. Motivated by this fact, a special class of the hybrid Ising-Heisenberg models [28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43] has been recently proposed, which overcome the afore-mentioned mathematical di...
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