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  Prokes, K.; Ressouche, E.; Mohan, A.; Wolter, A.U.B.; Büchner, B.; Hess, C.: Magnetic structure of La₈Cu₇O₁₉. Physical Review B 95 (2017), p. 024405/1-9

10.1103/PhysRevB.95.024405
Open Accesn Version

Abstract:
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 μB. 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 character.