Antiferromagnetic spin-1/2 chains in (NO)Cu(NO3)3: a microscopic study

We report on the microscopic model of the recently synthesized one-dimensional quantum magnet (NO)Cu(NO3)3. Applying density functional theory band structure calculations, we obtain a leading antiferromagnetic exchange coupling J ~ 200 K, which runs via NO3 groups forming spin chains along the b direction. Much weaker couplings J' ~ 2 K link the chains into layers in a non-frustrated manner. Our calculations do not support the earlier conjecture on an anisotropic frustrated square lattice physics in (NO)Cu(NO3)3. In contrast, the model of uniform spin chains leads to a remarkably good fit of the experimental magnetic susceptibility data, although the low-temperature features of the intrinsic magnetic susceptibility measured by electron spin resonance might call for extension of the model. We outline possible experiments to observe the suggested long-range magnetic ordering in (NO)Cu(NO3)3 and briefly compare this compound to other spin-1/2 uniform-chain systems.