Nature of the spin dynamics and 1/3 magnetization plateau in azurite

TL;DR

This study investigates the spin dynamics and magnetization plateau in azurite, revealing a dimer-monomer state with specific effective couplings, using heat capacity and neutron scattering techniques.

Contribution

It provides detailed experimental evidence and analysis of the spin state and couplings in azurite's 1/3 magnetization plateau phase, elucidating the microscopic interactions.

Findings

The 1/3 magnetization plateau is a dimer-monomer state.

Effective spin couplings are quantified as J_{mono}/k_B=10.1 K and J_{dimer}/k_B=1.8 K.

Microscopic exchange interactions include J_1, J_2, and J_3 with specific values.

Abstract

We present a specific heat and inelastic neutron scattering study in magnetic fields up into the 1/3 magnetization plateau phase of the diamond chain compound azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$. We establish that the magnetization plateau is a dimer-monomer state, {\it i.e.}, consisting of a chain of $S = 1/2$ monomers, which are separated by $S = 0$ dimers on the diamond chain backbone. The effective spin couplings $J_{mono}/k_B = 10.1(2)$ K and $J_{dimer}/k_B = 1.8(1)$ K are derived from the monomer and dimer dispersions. They are associated to microscopic couplings $J_1/k_B = 1(2)$ K, $J_2/k_B = 55(5)$ K and a ferromagnetic $J_3/k_B = -20(5)$ K, possibly as result of $d_{z^2}$ orbitals in the Cu-O bonds providing the superexchange pathways.