Spin Chains with Highly Quantum Character through Strong Covalency in Ca3CrN3

The insulating transition metal nitride Ca3CrN3 consists of sheets of triangular [CrN3]6- units with C2v symmetry that are connected via quasi-1D zigzag chains. Due to strong covalency between Cr and N, Cr3+ ions are unusually low-spin, and S = 1/2. Magnetic susceptibility measurements reveal dominant quasi-1D spin correlations with very large nearest-neighbor antiferromagnetic exchange J = 340 K and yet no sign of magnetic order down to T = 0.1 K. Density functional theory calculations are used to model the local electronic structure and the magnetic interactions, supporting the low-spin assignment of Cr3+ that is driven by strong π donation from the nitride ligands. The surprising failure of interchain exchange to drive long-range magnetic order is accounted for by the complex connectivity of the spin chain pairs that further frustrates order. Our combined results establish Ca3CrN3 as a nearly ideal manifestation of a quantum spin chain whose dynamics remain unquenched down to extraordinarily low temperatures despite strong near-neighbor exchange coupling.