COMPETITION BETWEEN THE SINGLET-SPIN LIQUID STATE AND THE MAGNETIC GROUND STATE IN A TWO-CHAIN SPIN-1/2 ANTIFERROMAGNETIC LADDER COMPOUND LACUO2.5 - A CU-63 NMR STUDY

摘要

The magnetic characteristics of LaCuO2.5 comprising an antiferromagnetic two-chain spin-1/2 ladder have been investigated by Cu-63 NMR measurements. The ground state of this compound was suggested from susceptibility measurements to be the singlet-spin liquid state. The present experiments have, however, revealed that LaCuO2.5 is not in such a spin-liquid state, but rather a magnetic ordering takes place below T-N similar to 110 K as evidenced by the large enhancement of the nuclear spin-lattice relaxation rate, (1/T-1) and of the spin-echo decay rate, 1/T-2 leading to the disappearance of the Cu NMR signal. This magnetic ordered state has been found to be suppressed by substituting Sr for La by 5%, i.e., by hole doping. [References: 16]