LONG-RANGE MAGNETIC ORDER OF THE ER IONS IN ER2BA4CU7O14.92

Neutron-diffraction investigations at temperatures down to 25 mK were performed for the high-temperature superconductor Er2Ba4Cu7O14.92 (Er- 247), T-c=89 K on a polycrystalline sample prepared by a sol-gel techn ique. Below T-N=0.54 K, a three-dimensional antiferromagnetic ordering of the Er ions corresponding to a propagation vector k=(1/2,0,0) and a finite correlation length of about 130 Angstrom along the c axis hav e been found. The magnetic Er moments are oriented parallel to the b a xis. This work proves that Er-247 shows a long-range magnetic ordering .