Abstract
Magnetic d.c. and a.c. susceptibility and lattice constant measurements were performed in the normal state of YBa 2Cu 3− x Mn x O 7−δ with Mn concentrations x = 0.075, 0.15, 0.2, 0.25 and 0.3. The orthorhombic structure 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 different behaviour above and below the x = 0.2 Mn in the YBCO. The measurements of the d.c. susceptibility were analysed using a Curie-Weiss law with a temperature-independent background. The effective magnetic moment obtained per Mn atom, p Mn = 3.29 μ B, suggests the presence of a 4+ oxidation state. The variation of the Curie paramagnetic temperature θ for different x is associated with an antiferromagnetic exchange interaction between the Mn ions. A regular trend of p eff.tot 2 and T c as a function of x suggest that below x = 0.2 Mn ions are substituted in the Cu(1) positions.
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