INTERPLANAR COUPLING BETWEEN CUO2 PLANES IN EU1.9Y0.1CUO4 SINGLE-CRYSTALS

We present detailed de magnetization and magnetic resonance for an Eu1 .9Y0.1CuO4 Single crystal. The substitution of Eu by non-magnetic Y3allowed us to measure the weak ferromagnetic properties of the ordered Cu lattice with the interference of just the weakly magnetic Eu3+ ion s. A Neel temperature, T-N similar to 250 K, and a value of the satura tion magnetization m(s) (6 K) similar to 5 x 10(-3) mu(B)/Cu-atom, wer e obtained from the data. We observed anisotropy effects in the magnet ization within the CuO2 planes. The data were analyzed using a four su blattice magnetic free energy for the ordered Cu spins. From the magne tic resonance data taken at Q band (34 GHz) we have determined the tem perature dependence of the out-of-plane and in-plane anisotropy fields . Using an average value for the exchange field [H-c] = 80 G, we estim ate a value for the interplanar exchange constant, J(perpendicular to) = 19 mK, similar to the values previously found in La2CuO4 and Y2CuO4 .