OBSERVATION OF A SPIN GAP IN SRCU2O3 COMPRISING SPIN-1/2 QUASI-1D 2-LEG LADDERS

Magnetic properties of SrCu2O3 and Sr2Cu3O5, containing two-leg and three-leg S=12 ladders made of antiferromagnetic Cu-O-Cu linear bonds, were investigated. The susceptibility of the two-leg ladder material, SrCu2O3, is characteristic of thermal excitation from a nonmagnetic ground state with a spin gap of about 420 K, while the susceptibility of Sr2Cu3O5, containing three-leg ladders, reflects a gapless spin excitation spectrum. The temperature dependence of the nuclear-spin lattice relaxation rate, 1T1, of Cu63 NMR also indicates the existence of a spin gap only for SrCu2O3. The spin gap we observed for SrCu2O3 confirms a recent theoretical prediction for the magnetic behavior of spin = antiferromagnetically coupled Heisenberg chains. © 1994 The American Physical Society.