Magnetic-field–temperature phase diagram of alternating ferrimagnetic chains: Spin-wave theory from a fully polarized vacuum

W. M. da Silva and R. R. Montenegro-Filho
Phys. Rev. B 96, 214419 – Published 13 December 2017

Abstract

Quantum critical (QC) phenomena can be accessed by studying quantum magnets under an applied magnetic field (B). The QC points are located at the end points of magnetization plateaus and separate gapped and gapless phases. In one dimension, the low-energy excitations of the gapless phase form a Luttinger liquid (LL), and crossover lines bound insulating (plateau) and LL regimes, as well as the QC regime. Alternating ferrimagnetic chains have a spontaneous magnetization at T=0 and gapped excitations at zero field. Besides the plateau at the fully polarized (FP) magnetization, due to the gap there is another magnetization plateau at the ferrimagnetic (FRI) magnetization. We develop spin-wave theories to study the thermal properties of these chains under an applied magnetic field: one from the FRI classical state and another from the FP state, comparing their results with quantum Monte Carlo data. We deepen the theory from the FP state, obtaining the crossover lines in the T vs B low-T phase diagram. In particular, from local extreme points in the susceptibility and magnetization curves, we identify the crossover between an LL regime formed by excitations from the FRI state to another built from excitations of the FP state. These two LL regimes are bounded by an asymmetric domelike crossover line, as observed in the phase diagram of other quantum magnets under an applied magnetic field.

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  • Received 8 October 2017

DOI:https://doi.org/10.1103/PhysRevB.96.214419

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

W. M. da Silva and R. R. Montenegro-Filho*

  • Laboratório de Física Teórica e Computacional, Departamento de Física, Universidade Federal de Pernambuco, 50760-901 Recife-PE, Brazil

  • *rene.montenegro@ufpe.br

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Vol. 96, Iss. 21 — 1 December 2017

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