Ab initio determination of exchange integrals and Neel temperature in the chain cuprates

TL;DR

This study uses ab initio calculations to determine exchange interactions and Neel temperatures in chain cuprates, revealing significant interchain coupling effects and challenging traditional spin-wave theory predictions.

Contribution

It provides the first ab initio estimates of exchange integrals in chain cuprates and links these to magnetic ordering temperatures, highlighting a 1D to 2D crossover.

Findings

J_a is comparable to in-plane J in layered cuprates

J_a/J_b ratio is approximately 250-400

Neel temperature T_N is independent of J_c, contradicting spin-wave theory

Abstract

We report ab initio quantum chemical cluster calculations of the chain (J_a) and the largest interchain (J_b) Heisenberg exchange of the chain cuprates Ca_2CuO_3 and Sr_2CuO_3. We find that J_a is comparable to the in-plane J in layered cuprates and J_a/J_b ~250-400. Using recent theory we obtain close agreement with experiment for the staggered moments and the critical temperatures. This implies that T_N does not depend on the third parameter J_c << J_b, and cannot be calculated using spin-wave theory. We propose an explanation for this interms of a 1D->2D cross-over.