Conversion of a glassy antiferromagnetic-insulating phase to an equilibriumferromagnetic-metallic phase by devitrification and recrystallization in Al substitutedPr0.5Ca0.5MnO3

Abstract

We show that Pr0.5Ca0.5MnO3 with 2.5%Al substitution and La0.5Ca0.5MnO3 (LCMO) exhibit qualitatively similar and visibly anomalousM–H curves at low temperature. Magnetic field causes a broad first order but irreversibleantiferromagnetic (AF)–insulating (I) to ferromagnetic (FM)–metallic (M) transition inboth and gives rise to a soft FM state. However, the low temperature equilibrium state ofPr0.5Ca0.5Mn0.975Al0.025O3 (PCMAO) is FM-M whereas that of LCMO is AF-I. In both systems the respectiveequilibrium phase coexists with the other phase with contrasting order, which is not inequilibrium, and the cooling field can tune the fractions of the coexisting phases. It isshown earlier that the coexisting FM-M phase behaves like ‘magnetic glass’ in LCMO. Herewe show from specially designed measurement protocols that the AF-I phase ofPCMAO has all the characteristics of magnetic glassy states. It devitrifies onheating and also recrystallizes to an equilibrium FM-M phase after annealing. Thisglass-like AF-I phase also shows a similar intriguing feature observed in FM-Mmagnetic glassy state of LCMO, that when the starting coexisting fraction ofglass is larger, successive annealing results in a larger fraction of the equilibriumphase. This similarity between two manganite systems with contrasting magneticorders of respective glassy and equilibrium phases points to a possible universality.