Relationship between morphological and physical properties in nanostructured CuMnO₂

Abstract

In this study, crednerite CuMnO2 nanostructures were prepared using a hydrothermal method at 100 °C with different amounts of NaOH mineralizator. Obtained nanostructured crednerite CuMnO2 with monoclinic structure (space group C2/m) exhibits two kinds of morphologies: nanobelts of the length of 1 - 1.5 µm and thickness of 15 - 25 nm, and nanoplatets being of 50 - 70 nm in diameter. Comparative studies of the preprepared samples reveal an intimate relationship between morphological and physical properties in nanostructured CuMnO2. A low NaOH concentration favours elongated crystal growth along the c-axis, creating nanobelt-shaped morphology. On the other hand, a strong base solution promotes the formation of nanoplates. Unique morphologies of nanostructured CuMnO2 affect distinct spectroscopic and magnetic properties. The nanobelt-shaped sample is characterized by the Raman active A1g mode at 637 cm-1 and a modified Curie-Weiss bahaviour. This phase exhibits two successive magnetic phase transitions: ferromagnetically at 9.2 K and antiferromagnetically at 42 K. Conversely, the nanoplate-shaped sample behaves typically as those reported in the literature, namely, the Raman active A1g mode at 688 cm-1 and low-dimensional magnetism with antiferromagnetic ordering below 62 K. The variation in the magnetic properties is presumably associated to the partial oxidation of Cu1+ and Mn2+ in the nanoplate-shaped sample compared to the divalent state of Cu2+ and trivalent Mn3+ ions in the nanobelt-shaped one.