Observation of ferroelectricity and structure-dependent magnetic behavior in novel one-dimensional motifs of pure, crystalline yttrium manganese oxides

Multiferroic materials, such as nanostructured h-YMnO₃, are expected to fulfill a crucial role as active components of technological devices, particularly for information storage. Herein, we report on the template mediated sol-gel synthesis of unique one-dimensional nanostructured motifs of hexagonal phase YMnO₃, possessing a space group of P6₃cm. We found that the inherent morphology of the as-obtained h-YMnO₃ nanostructures was directly impacted by the chemical composition of the employed membrane. Specifically, the use of anodic alumina and polycarbonate templates promoted nanotube and nanowire formation, respectively. Isolated polycrystalline nanotubes and single crystalline nanowires possessed diameters of 276 ± 52 nm, composed of 17 nm particulate constituent grains, and 125 ± 21 nm, respectively, with lengths of up to several microns. The structures and compositions of all our as-prepared products were probed by XRD, SEM, HRTEM, EXAFS, XANES, SAED, and far-IR spectroscopy. In the specific case of nanowires, we determined that the growth direction was mainly along the c-axis and that discrete, individual structures gave rise to expected ferroelectric behavior. Overall, our YMnO₃ samples evinced the onset of a spin-glass transition at 41 ± 1 K for both templateless bulk control and nanowire samples but at 26 ± 3 K for nanotubes. Interestingly, only the as-synthesized crystalline nanotubular mesh gave rise to noticeably enhanced magnetic properties (i.e., a higher magnetic moment of 3.0 μ_B/Mn) as well as a lower spin-glass transition temperature, attributable to a smaller constituent crystallite size. Therefore, this work not only demonstrates our ability to generate viable one-dimensional nanostructures of a significant and commercially relevant metal oxide but also contributes to an understanding of structure-property correlations in these systems.