Magnetization plateaus and enhanced magnetocaloric effect of a spin-1/2 Ising-Heisenberg and Heisenberg double sawtooth ladder with four-spin interaction

TL;DR

This paper investigates the ground state, entropy, and magnetocaloric effect of a complex spin ladder model, revealing a quadruple point with enhanced cooling effects and comparing quantum and classical versions to understand magnetic behaviors.

Contribution

It introduces a detailed analysis of a spin-1/2 Ising-Heisenberg double sawtooth ladder with four-spin interactions, identifying a quadruple point and comparing quantum and classical models.

Findings

Identification of a quadruple point in the phase diagram.

Enhanced magnetocaloric effect near the quadruple point.

Existence of intermediate magnetization plateaus in the quantum model.

Abstract

The ground state, the entropy and the magnetic Gr\"uneisen parameter of the antiferromagnetic spin-1/2 Ising-Heisenberg model on a double sawtooth ladder are rigorously investigated using the classical transfer-matrix technique. The model includes the XXZ interaction between the interstitial Heisenberg dimers, the Ising coupling between nearest-neighbor spins of the legs and rungs, and additional cyclic four-spin Ising term in each square plaquette. For a particular value of the cyclic four-spin exchange we found in the ground-state phase diagram of the Ising Heisenberg ladder a quadruple point, at which four different ground states coexist together. During an adiabatic demagnetization process a fast cooling accompanied with an enhanced magnetocaloric effect can be detected nearby this quadruple point. The ground-state phase diagram of the Ising-Heisenberg ladder is confronted with the zero-temperature magnetization process of the purely quantum Heisenberg ladder, which is calculated by using exact diagonalization (ED) based on the Lanczos algorithm for a finite-size ladder of 24 spins and the density-matrix renormalization group (DMRG) simulations for a finite-size ladder with up to 96 spins. Some indications of existence of intermediate magnetization plateaus in the magnetization process of the full Heisenberg model for a small but non-zero four-spin Ising coupling were found. The DMRG results reveal that the quantum Heisenberg double sawtooth ladder exhibits a quantum Luttinger spin-liquid phase that is absent in the Ising-Heisenberg counterpart model. Except this difference the magnetic behavior of the full Heisenberg model is quite analogous to its simplified Ising-Heisenberg counterpart and hence, one may bring insight into the fully quantum Heisenberg model from rigorous results for the Ising-Heisenberg model.