Emergence of ferromagnetism and metallicity in Pr0.5Sr0.5MnO3 nanoparticles

Abstract

In this paper, we have studied low-temperature magnetic properties and transport dynamics of half-doped Pr0.5Sr0.5MnO3 (PSMO) nano-manganite. Nanoparticles with different average grain sizes are synthesized using chemical pyrophoric reaction route and exhibit same crystal structure. It is reported that particle size reduction in half-doped PSMO manganite interestingly leads to ferromagnetic (FM) metallic behavior which is accompanied by coupled positive magnetoresistance (PMR) (up to 9%) at fields (H ≤ 1kOe at 50K) and negative magnetoresistance (NMR) (∼59% at 100K) at 80kOe fields. Interestingly, maximum PMR is appeared at much lower than the critical field (30kOe) for the melting of insulating -antiferromagnetic (AFM) ordered state. Moreover, it is found that low-temperature AFM-FM phase transition, TN ∼ 135K is smeared out with reduction of particle size; however, the transition is prominent in bulk material. A metastable magnetic state with a mixed fraction of FM and AFM phases is observed below TN. Superparamagnetic (SPM) behavior of PSMO nanoparticles has been revealed by probing ac-susceptibility measurements. Low-temperature transport dynamics has been investigated through four probe resistivity and magneto-transport measurements. A size-induced insulating-metallic phase transition is observed on nano dimension in the range of 125-155K under high magnetic fields; however, the bulk counterpart remains insulating over the entire temperature range. The non-trivial electronic- and magnetotransport properties are explained by the inter-grain spin-polarized hopping mechanism through double exchange (DE) interactions. These issues have been revisited and discussed in the framework of enhanced surface disorder, where surface spins plays the crucial role for inter-grain transport dynamics in nanometric dimension. We believe the present field dependent MR holds excellent potential for future spintronic devices and manifests the exotic properties of strongly correlated materials.