MAGNETIC STUDIES ON MN-SUBSTITUTED Y-BA-CU-O

Magnetic d.c. and a.c. susceptibility and lattice constant measurement s were performed in the normal state of YBa2Cu3-xMnxO7-delta with Mn c oncentrations x=0.075, 0.15, 0.2, 0.25 and 0.3. The orthorhombic struc ture is preserved throughout the substitution range and some amount of impurity phases were evidenced in the samples with x>0.2. The inter- and intragrain properties from a.c. susceptibility measurements show d ifferent behaviour above and below the x=0.2 Mn in the YBCO. The measu rements of the d.c. susceptibility were analysed using a Curie-Weiss l aw with a temperature-independent background. The effective magnetic m oment obtained per Mn atom, p(Mu)=3.29 mu(B), suggests the presence of a 4+ oxidation state. The variation of the Curie paramagnetic tempera ture B for different x is associated with an antiferromagnetic exchang e interaction between the Mn ions. A regular trend of p(effect)(2) and T-c as a function of x suggest that below x=0.2 Mn ions are substitut ed in the Cu(1R) positions.