Tuning colossal magnetoresistance through A-site ionic radius in polycrystalline Gd0.5Ca0.5−<i>x</i>Sr<i>x</i>MnO3 (<i>x</i> = 0.0–0.5) systems

The magnetotransport properties of polycrystalline Gd0.5Ca0.5−xSrxMnO3 systems reveal a significant enhancement in magnetoresistance with increasing A-site ionic radius, transitioning from “Ca” to “Sr.” Notably, Gd0.5Ca0.5MnO3 exhibits only a weak magnetoresistance, while complete substitution of Ca2+ with the larger Sr2+ ion in Gd0.5Sr0.5MnO3 results in a striking colossal magnetoresistance. This contrasting behavior highlights the critical role of the A-site divalent cation size in modulating the electronic bandwidth, suppressing charge-orbital ordering, and governing the interplay between competing magnetic and electronic ground states. Materials exhibiting such large magnetoresistance are of great interest for various spintronic applications. In polycrystalline Gd0.5Sr0.5MnO3 (GSMO), an exceptionally high magnetoresistance of 109% is observed at 10 K under a 70 kOe magnetic field, significantly exceeding the values reported for single-crystalline GSMO under similar conditions. Although all studied samples exhibit charge ordering, colossal magnetoresistance is exclusive to GSMO. This phenomenon can be attributed to a magnetic-field-induced transition from a charge-ordered antiferromagnetic insulating state to a ferromagnetic metallic state.