Magnetic order of the Cu planes and chains in RBa2Cu3O6+x

Polarized and unpolarized neutron-diffraction measurements have been taken to determine the magnetic structure of the Cu spins in the RBa2Cu3O6+x system as a function of temperature. Most of the results have been obtained on two (semiconducting) oxygen-deficient single crystals of composition NdBa2Cu3O6.1 and NdBa2Cu3O6.35. On cooling from the paramagnetic state, the Cu-O ''plane'' layers first order at a Neel temperature TN1 in a simple antiferromagnetic arrangement of spins, with TN1=430 K for x=0.1 and TN1=230 K for x=0.35, and with a saturated moment of ∼0.65μB. At a lower temperature TN2 the Cu ''chain'' layer also orders, with TN2=80 and 10 K for x=0.1 and 0.35, respectively. Hence both transition temperatures decrease with increasing oxygen concentration in this range of x, and the qualitative behavior for these two samples is found to be identical