Charge-Ordering and Magnetic Transitions in Nanocrystalline Half-Doped Rare Earth Manganite HoCaMnO.

This work investigates nanostructured HoCaMnO, considered a model system of the LnCaMnO series of manganites with perovskite structures featuring small lanthanide (Ln) ions half-substituted by Ca ions. Here, we propose a modified hybrid sol-gel-solid-state approach to produce multiple samples with a single batch, obtaining very high crystalline quality and ensuring the same chemical composition, with an average particle size in the range 39-135 nm modulated on-demand by a controlled calcination process. Our findings evidence that, provided the crystalline structure is preserved, the charge-ordering transition can be observed even at the nanoscale. Additionally, this research explores the presence of glassy phenomena, which are commonly seen in this class of materials, to enhance our understanding beyond simplistic qualitative observations. Comprehensive characterization using DC and AC magnetometry, along with relaxation and aging measurements, reveals that the complex dynamics typical of glassy phenomena emerge only at the nanoscale and are not visible in the bulk counterpart. Nevertheless, the analysis confirms that even the sample with the smallest nanoparticles cannot be intrinsically classified as canonical spin glass.