Critical behavior in the perovskite-like system Y(Ni,Mn)O-3

The electrical and magnetic properties of the perovskite-type solid solutio n YNixMn1-xO3 have been studied at different temperatures and magnetic fiel ds. Electrical conductivity measurements have shown a semiconductor behavio r throughout the solid solution. The room temperature conductivity increase s with the Ni concentration until x = 1/3, and then decreases for higher Ni contents. The effective moment in the paramagnetic state shows a clear bre ak at x = x(crit) = 1/3, presenting a constant value at x less than or equa l to x(crit) and decreasing at higher nickel concentration. In the ordered state, other magnetic parameters show similar discontinuities versus the ni ckel content, such as a sudden increase of the magnetization at high field or a maximum in the coercive strength of the ferromagnetic-like M(H) loop. By charge-conservation arguments we can readily identify such critical valu e as an optimum conversion of Mn3+ into Mn4+, leading to the charge-balance formula Y3+[Ni-1/3(2+)(Mn0.53+Mn0.54+)(2/3)]O-3(2-), that is, equal amount s of Mn3+ and Mn4+ in the sample. Magnetic data shows that, at x less than or equal to x(crit), the solid solution behaves as a spin-glass and/or anti ferromagnetic system, while at x > x(crit), full ferromagnetic characterist ics are observed. (C) 2000 Elsevier Science Ltd. All rights reserved.