Magnetism of Ti 4+ diluted manganites La 1-x Pb x Mn 1-y Ti y O 3 (y≤x)

The effect of nonmagnetic Ti 4+ substitution for Mn 4+ on magnetic ordering of La 1-x Pb x Mn 1-y Ti y O 3 (x=0.15, 0.26, and 0.4; 0≤y≤x ) has been studied. The ferromagnetic transition temperature and the magnetization decrease with increasing amount of titanium. Complete substitution of Mn 4+ by Ti 4+ , for x=y, excludes the Mn 3+ -O-Mn 4+ double exchange. However, these compounds still show ferromagnetism if the dilution of the Mn sublattice by Ti is small enough (y≤0.2). This ferromagnetism probably originates from a ferromagnetic Mn 3+ -O-Mn 3+ superexchange. A thorough study of magnetic properties including AC magnetic susceptibility, magnetization, temperature dependence of coercivity and relaxation of remanent magnetization has been carried out and gives evidence of cluster spin glass behaviour for La 0.6 Pb 0.4 Mn 0.6 Ti 0.4 O 3 .