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In order to investigate the magnetic order of the copper moments in the monoclinic (distorted hexagonal) compound RbCuCl 3 we carried out neutron diffraction experiments using single crystals and powder samples. Below the Neel temperature T N =19.3 K a helimagnetic structure with the propagation vector k mon =(0, 0.5985, 0) was observed. The magnetic moments lie in the monoclinic ab -plane and rotate along the b -axis with a turning angle of ϑ =108° between the adjacent planes (± 1/2 b ). In the hexagonal representation the propagation vector corresponds to k hex =(0.2993, 0.2993, 0). This vector is close to k =(1/3, 1/3, 0) and therefore we deal with a distorted triangular antiferromagnet with partially released frustration. At 1.6 K the experimental magnetic moment of the copper atoms is μ exp =0.69(6) μ B . From susceptibility measurements with a SQUID magnetometer we derived the coupling constants of exchange interactions of the copper spins between ( J 0 =25(1) K) and within ( J 1 =−9(1) K) the stacked planes of triangles. |
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