High-Field Magnetism of the Spin-Ladder Material Na2Fe2(C2O4)3(H2O)2

Abstract

We report the results of our magnetic susceptibility, magnetization, and multi-frequency electron spin resonance (ESR) measurements on single crystals of the two-leg spin-ladder material Na 2 Fe 2 (C 2 O 4 ) 3 (H 2 O) 2 . Magnetization processes in magnetic fields up 53 T at 1.3 K paralell ( H ∥ a ) and perpendicular ( H ⊥ a ) to the leg direction show a gradual increase compared with those of the isomorphous compound Na 2 Co 2 (C 2 O 4 ) 3 (H 2 O) 2 , which was well explained by an isolated antiferromagnetic dimer model. Thus, we calculated the magnetic susceptibilities and magnetizations on the basis of a two-leg ladder model with a fictitious spin ( S ) one by a quantum Monte Carlo method and a density-matrix renormalization group method, respectively. These calculated results, however, did not agree well with the experimental ones. Therefore, we regarded Na 2 Fe 2 (C 2 O 4 ) 3 (H 2 O) 2 as an isolated S = 1 antiferromagnetic dimer with not only the anisotropy of the exchange interactions due to the tr...