Giant pressure dependence and dimensionality switching in a metal-organic quantum antiferromagnet

TL;DR

This study reveals how applying pressure to a metal-organic quantum antiferromagnet causes a continuous reduction in magnetic exchange interactions and induces a phase transition that switches the system's dimensionality from quasi-two-dimensional to one-dimensional.

Contribution

It demonstrates the pressure-induced dimensionality switching and detailed microscopic mechanisms in a metal-organic quantum antiferromagnet using experimental and theoretical methods.

Findings

Exchange interactions decrease by a factor of 2 under pressure.

A phase transition occurs above 18 kbar, reordering orbitals.

Dimensionality switches from Q2D to Q1D after transition.

Abstract

We report an extraordinary pressure dependence of the magnetic interactions in the metal-organic system [(CuF$_2$(H$_2$O)$_2$)$_2$pyrazine]. At zero pressure, this material realizes a quasi-two-dimensional (Q2D) spin-1/2 square-lattice Heisenberg antiferromagnet. By high-pressure, high-field susceptibility measurements we show that the dominant exchange parameter is reduced continuously by a factor of 2 upon compression. Above 18 kbar, a phase transition occurs, inducing an orbital re-ordering that switches the dimensionality, transforming the Q2D lattice into weakly coupled chains (Q1D). We explain the microscopic mechanisms for both phenomena by combining detailed x-ray and neutron diffraction results with quantitative modeling using spin-polarized density functional theory.