Spin-flop and antiferromagnetic phases of the ferromagnetic half-twist ladder compounds Ba3Cu3In4O12 and Ba3Cu3Sc4O12

TL;DR

This study models the magnetic phases of Ba3Cu3In4O12 and Ba3Cu3Sc4O12, revealing the coexistence of ferromagnetic, antiferromagnetic, and spin-flop phases through a combination of microscopic and phenomenological approaches.

Contribution

It introduces a combined microscopic and phenomenological model to accurately describe the magnetic phases and transitions in half-twist ladder compounds.

Findings

Identification of AFM, SF, and PM phases with sharp features in magnetization and heat capacity.

Quantitative agreement of the model with experimental magnetization and susceptibility data.

Determination of exchange interactions and anisotropy fields consistent with observed magnetic behavior.

Abstract

The title compounds have dominant ferromagnetic (FM) exchange interactions within one-dimensional (1D) half-twist ladders of s =1/2 Cu2^{+} ions and antiferromagnetic(AFM) interactions between ladders, leading to ordered 3D phases at temperatures below 20K. Here we show that a microscopic 1D model of the paramagnetic (PM) phase combined with a phenomenological model based on sublattice magnetization describes the observed temperature and field dependent magnetism. The model identifies AFM, spin-flop (SF) and PM phases whose boundaries have sharp features in the experimental magnetization M(T,H) and specific heat CP(T,H). Exact diagonalization (ED) of the 1D model, possible for 24 spins due to special structural features of half-twist ladders, yields the magnetization and spin susceptibility of the PM phase. AFM interactions between ladders are included at the mean-field level using the field, HAF, obtained from modeling the ordered phases. Isotropic exchange J1 = -135K and g-tensor g = 2.1 within ladders, plus exchange and anisotropy fields HAF and HA, describe the ordered phases, and are almost quantitative for the PM phase.