Magnetism of Ti4+ diluted manganites La1-xPbxMn1-yTiyO3 (y <= x)

The effect of nonmagnetic Ti4+ substitution for Mn4+ on magnetic ordering o f La1-xPbxMn1-yTiyO3 (x = 0.15,0.26, and 0.4; 0 less than or equal to y les s than or equal to x )has been studied. The ferromagnetic transition temper ature and the magnetization decrease with increasing amount of titanium. Co mplete substitution of Mn4+ by Ti4+, for x = y, excludes the Mn3+-O-Mn4+ do uble exchange. However, these compounds still show ferromagnetism if the di lution of the Mn sublattice by Ti is small enough (y less than or equal to 0.2). This ferromagnetism probably originates from a ferromagnetic Mn3+-O-M n3+ superexchange. A thorough study of magnetic properties including AC mag netic susceptibility, magnetization, temperature dependence of coercivity a nd relaxation of remanent magnetization has been carried out and gives evid ence of cluster spin glass behaviour for La0.6Pb0.4Mn0.6Ti0.4O3. (C) 2000 E lsevier Science B.V. All rights reserved.