MAGNETIC-PROPERTIES OF PNMA-R(2)BAZNO(5) OXIDES (R=SM,EU,DY AND HO)

In this work, we report DC susceptibility measurements in the range 1. 8-300 K on Pnma-R(2)BaZnO(5) oxides with R = Sm, Eu, Dyand Ho. Eu2BaZn O5 displays Van Vleck paramagnetism which corresponds to the singlet g round state F-7(0) of Eu+3 ions, with a spinorbit coupling constant va lue of lambda = 365(2) cm(-1). Sm2BaZnO5 also behaves as a Van Vleck p aramagnet, with the magnetic ground multiplet split under the crystal- field interaction. For this compound we found that the ground state co rresponds to an effective spin state S (+/- 1/2), with effective magne tic moment mu(eff) = 0.32(1)mu(B), and Van Vleck constant alpha(1) = 9 .2(2)x 10(-4) For R = Dy and Ho, the magnetic susceptibility obeys a C urie-Weiss law down to T = 1.8 K, with effective moments close to the free-ion values. The absence of magnetic ordering above 1.8 K, togethe r with the Curie temperatures theta(Dy) = -15.1(8) K and theta(Ho) = - 11.3(8) K of these compounds, indicate the existence of competing inte ractions that frustrate the magnetic ordering.