Design of a Random Quantum Spin Chain Paramagnet: Sr ₃ CuPt 0.5 Ir 0.5 O ₆

A new class of magnetic behavior, random quantum spin chain paramagnetism, has been observed in the one-dimensional compound Sr 3 CuPt 1- x Ir x O 6 . A random quantum spin chain system has S = ½ spins coupled by Heisenberg exchange interactions that are randomly ferromagnetic or antiferromagnetic between neighbors along the chain. This condition was fulfilled by members of the solid solution Sr 3 CuPt 1- x Ir x O 6 ( x = 0, 0.25, 0.50, 0.75, and 1), whose end-members, Sr 3 CuPtO 6 and Sr 3 CuIrO 6 , are antiferromagnetic and ferromagnetic, respectively. Magnetic susceptibility data for the solid solution Sr 3 CuPt 1- x Ir x O 6 ( x = 0, 0.25, 0.50, 0.75, and 1) were collected and were found to be in excellent agreement with a theoretical model.