Magnetic structure of La8Cu7O19

Themagnetic structure of the five leg ladder compound La8Cu7O19 has been determined using single crystalline neutron diffraction. The material orders antiferromagnetically with the propagation vector q 1 2 , 1 2 ,0 below TN 102.5 3 K. Above this temperature the magnetic susceptibility corresponds indeed to that of a five legS 1 2 spin ladder, assuming isotropic couplings along the rungs and the legs [J kB 194 3 K]. Crystallographically, the Cu magnetic moments divide into two subsystems, depending on the environment. Moments situated at centers of octahedra built up by oxygens orient along the b axis and couple to neighboring moments antiferromagnetically, whereas those creating a complicated ribbon structure possess all three Cartesian components. All Cu moments are found to have magnitudes between 0.69 and 1.32 amp; 956;B. Thus, it is seen that the five leg ladder La8Cu7O19 exhibits long range antiferromagnetic ordering and possesses a rather complicated magnetic structure which has a noncollinear characte