Extended Moment Formation and Second Neighbor Coupling in Li$_2$CuO$_2$

TL;DR

This study uses local spin density calculations to reveal that Li$_2$CuO$_2$ exhibits unusually large magnetic moments, significant oxygen contributions, and dominant second neighbor couplings, driven by specific orbital hybridizations.

Contribution

It uncovers the origin of large magnetic moments and coupling patterns in Li$_2$CuO$_2$ due to a well-defined $d_{yz}$ orbital with strong O $p_{\sigma}$ character, advancing understanding of low-dimensional cuprates.

Findings

Largest ordered moment among low-dimensional cuprates (0.92 μ_B)

40% of the moment on oxygen ions

Second neighbor couplings exceed nearest neighbor couplings

Abstract

Comprised of ferromagnetic edge-sharing CuO$_2$ chains that order in antialigned fashion at T$_N$=9 K, Li$_2$CuO$_2$ is found from local spin density calculations to display several surprising characteristics: (1) the ordered moment/f.u. of 0.92 $\mu_B$ is the largest for any low dimensional cuprate system, in agreement with experiment, (2) 40% of this moment lies on the neighboring O ions, making it the largest oxygen moment yet reported, and (3) the second neighbors couplings are larger than nearest neighbors couplings. All of these phenomena arise naturally due to a well defined effective $d_{yz}$ type orbital that includes very strong O $p_{\sigma}$ character. We interpret the large moment as surviving reduction by quantum fluctuations due to extension caused by the $d-p$ hybridization.