Structural and magnetic characterization of the complete delafossite solid solution (CuAlO[subscript 2])[subscript 1;#8722;x](CuCrO[subscript 2])[subscript x]

We have prepared the complete delafossite solid solution series between diamagnetic CuAlO{sub 2} and the t{sub 2g}{sup 3}frustrated antiferromagnet CuCrO{sub 2}. The evolution with composition x in CuAl{sub 1-x}Cr{sub x}O{sub 2} 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 {mu}{sub eff} is equal to the Cr{sup 3+} spin-only S = 3/2 value throughout the entire solid solution. {Theta}{sub CW} is negative, indicating that the dominant interactions are antiferromagnetic, and its magnitude increases with Cr substitution. For dilute Cr compositions, the nearest-neighbor exchange coupling constant J{sub BB} was estimated by mean-field theory to be 3.0 meV. Despite the sizable {Theta}{sub CW}, long-range antiferromagnetic order does not develop until x is almost 1, and is preceded by glassy behavior. The data presented here, and those 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 CuCrO{sub 2} above its Neel temperature, consistent with its magnetic frustration. Uncompensated short-range behavior is present in the Al-substituted samples and is likely a result of chemical disorder.