Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO_4(OH) (A = Na, K)

TL;DR

This study compares the crystal structures and magnetic interactions of two isotypic quasi-one-dimensional cuprates, revealing how different orbital arrangements significantly influence their magnetic coupling strengths and types.

Contribution

It demonstrates the crucial impact of orbital arrangements on magnetic interactions in cuprates through comparative analysis of NaCuMoO_4(OH) and KCuMoO_4(OH).

Findings

NaCuMoO_4(OH) exhibits ferromagnetic J_1 and antiferromagnetic J_2 interactions.

KCuMoO_4(OH) shows strong antiferromagnetic J_1 with negligible J_2.

Orbital arrangements critically determine magnetic coupling in cuprates.

Abstract

A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO_4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO_4(OH) and the already-known Na-analogue, NaCuMoO_4(OH), are isotypic, comprising chains of Cu^{2+} ions in edge-sharing CuO_4(OH)_2 octahedra. Despite the structural similarity, their magnetic properties are quite different because of the different arrangements of d_{x2-y2} orbitals carrying spins. For NaCuMoO_4(OH), d_{x2-y2} orbitals are linked by superexchange couplings via two bridging oxide ions, which gives a ferromagnetic nearest-neighbor interaction J_1 of -51 K and an antiferromagnetic next-nearest-neighbor interaction J_2 of 36 K in the chain. In contrast, a staggered d_{x2-y2} orbital arrangement in KCuMoO_4(OH) results in superexchange couplings via only one bridging oxide ion, which makes J_1 antiferromagnetic as large as 238 K and J_2 negligible. This comparison between the two isotypic compounds demonstrates an important role of orbital arrangements in determining the magnetic properties of cuprates.