Structural and magnetic characterization of the complete delafossite solid solution (CuAlO2){1-x}(CuCrO2){x}

TL;DR

This study investigates the structural and magnetic evolution in the complete CuAl(1-x)Cr(x)O2 delafossite solid solution, revealing how composition influences magnetic interactions, frustration, and ordering.

Contribution

It provides comprehensive experimental data on the structural and magnetic properties across the entire solid solution series, highlighting the effects of chemical disorder and dilution on magnetic frustration.

Findings

Unit cell parameters follow Vegard's law with increasing x.

Effective magnetic moment remains Cr^3+ spin-only value throughout.

Long-range antiferromagnetic order appears only at large x, preceded by glassy behavior.

Abstract

We have prepared the complete delafossite solid solution series between diamagnetic CuAlO2 and the t2g^3 frustrated antiferromagnet CuCrO2. The evolution with composition x in CuAl(1-x)Cr(x)O2 of the crystal structure and magnetic properties has been studied and is reported here. The room-temperature unit cell parameters follow the Vegard law and increase with x as expected. The effective moment is equal to the Cr^3+ spin-only S = 3/2 value throughout the entire solid solution. Theta is negative, indicating that the dominant interactions are antiferromagnetic, and its magnitude increases with Cr substitution. For dilute Cr compositions, J_BB was estimated by mean-field theory to be 2.0 meV. Despite the sizable Theta, long-range antiferromagnetic order does not develop until very large x, and is preceeded by glassy behavior. Data presented here, and that on dilute Al-substitution from Okuda et al., suggest that the reduction in magnetic frustration due to the presence of non-magnetic Al does not have as dominant an effect on magnetism as chemical disorder and dilution of the magnetic exchange. For all samples, the 5 K isothermal magnetization does not saturate in fields up to 5 T and minimal hysteresis is observed. The presence of antiferromagnetic interactions is clearly evident in the sub-Brillouin behavior with a reduced magnetization per Cr atom. An inspection of the scaled Curie plot reveals that significant short-range antiferromagnetic interactions occur in CuCrO2 above its Neel temperature, consistent with its magnetic frustration. Uncompensated short-range interactions are present in the Al-substituted samples and are likely a result of chemical disorder.