Synthesis, Structural and magnetic properties of the solid solution (CuCl1-xBrx)LaNb2O7 (0<x<1)

TL;DR

This study synthesizes and characterizes the solid solution (CuCl1-xBrx)LaNb2O7, revealing how gradual Br substitution influences structural parameters and induces antiferromagnetic order, bridging the quantum spin states of the end compounds.

Contribution

It provides the first comprehensive analysis of structural and magnetic evolution across the (CuCl1-xBrx)LaNb2O7 series, highlighting the transition from quantum disordered to ordered states.

Findings

Vegards law describes cell parameter variation with x

5% Br induces antiferromagnetic order at 7 K

TN increases linearly with x up to 1

Abstract

The two-dimensional (2D) quantum spin system (CuCl)LaNb2O7 has a spin-singlet ground state with a gap of 2.3 meV, while the isostructural material (CuBr)LaNb2O7 displays collinear antiferromagnetic order at TN = 32 K. Here we report on the synthesis of solid solution (CuCl1-xBrx)LaNb2O7 (0 < x < 1), and its structural and magnetic properties by means of magnetic susceptibility, high-field magnetization, and neutron diffraction studies. The x-dependence of cell parameters follows Vegards law, verifying the uniform distribution of Cl and Br atoms at the halide site, though a more complex structural evolution is inferred from an opposing correlation between the intra- and interlayer cell distances (vs. x). 5%-Br substitution is found to induce antiferromagnetic order with TN = 7 K, consistent with a recent mSR study, and the magnetic structure is collinear, having a significantly reduced moment. Further Br substitution leads to a linear increase in TN up to x = 1. These results indicate that (CuCl)LaNb2O7 is located in the vicinity of the quantum phase boundary.