Vigorous thermal excitations in a double-tetrahedral chain of localized Ising spins and mobile electrons mimic a temperature-driven first-order phase transition

Abstract

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.

Magnetic Grüneisen parameter and magnetocaloric properties of a coupled spin–electron double-tetrahedral chain

“…(9) and (10) in Ref. [16]). At this stage, the exact calculation of the partition function Z of the spin-electron tetrahedral chain is formally completed, because the partition function Z I of the spin-1/2 Ising linear chain in a magnetic field is known [25,26].…”

“…As has been shown in our previous works [15,16], the considered 1D spin-electron system provides a suitable prototype model for theoretical investigation of the relation between the groundstate degeneracy and the cooling efficiency of the system during the adiabatic (de)magnetization.…”

“…From this point of view, the partition function of the system can exactly be derived within the generalized decoration-iteration mapping transformation [21][22][23][24] (as described in our previous work [16]). As a result, one obtains a simple relation between the partition function Z of the investigated spin-electron tetrahedral chain and the partition function Z I of the uniform spin-1/2 Ising linear chain with the effective nearest-neighbour coupling J ef f and the effective magnetic field H ef f :…”

“…(10) of Ref. [16]. The so-called magnetic Grüneisen parameter Γ H , which can be calculated from the relation (see Ref.…”

“…Of particular interest is the investigation of the MCE in various one-dimensional (1D) quantum spin systems [4][5][6][7][8][9][10][11][12][13] or hybrid spin-electron models [14][15][16]. The reason is a possibility of obtaining the exact analytical or numerical results as well as a potential use of these models for the explanation of MCE data measured for real magnetic compounds.…”