Analysis of nearest-neighbor spin exchange interactions by molecular orbital calculations:: anisotropic spin exchange interactions in MV3O7 (M = Cd, Ca, Sr) and α′-NaV2O5

Spin-dimer analysis was carried out for the room temperature structures of MV3O7 (M = Cd, Ca, Sr) and the 15 K structure of alpha'-NaV2O5 reported by Ludecke et al. to examine the relative magnitudes of the nearest-neighbor spin exchange interactions between their unpaired spins. Our analysis explains why the magnetic susceptibility of the stripe spin structure of MV3O7 (M = Cd, Ca, Sr) exhibits a one-dimensional spin-1/2 Heisenberg chain-like behavior. Our study indicates that the 15 K crystal structure of (alpha'-NaV2O5 is likely to have a spin gap and exhibit spin frustration. The predicted spin frustration is not consistent with the singlet ground state expected for a spin-Peierls system. (C) 2000 Elsevier Science Ltd. All rights reserved.