The main scientific results of the project:
1. Phase-pure samples of the alkali manganites Na0.22MnO2·0.39H2O and K0.6MnO2·0.48H2O with the birnessite structure were synthesized by the sol-gel method. The crystal structure, and static and dynamic magnetic properties of these compounds were investigated in detail. A combination of DC and AC magnetic susceptibility measurements and magnetization decay measurements revealed cluster glass behavior below the freezing temperature of 4 K for Na-birnessite and 6 K for K-birnessite. The frequency dependence of the freezing temperature was analyzed on the basis of dynamic scaling laws including the critical slowing down formula and the Vogel-Fulcher law, which further confirmed the formation of cluster glass states in both compounds.
2. The largest single crystals of potassium manganite reported thus far, with composition K0.31MnO2·0.41H2O were grown and studied in detail. For the first time, structural characterization was carried out using a combination of single-crystal XRD and high-resolution scanning TEM, which revealed a number of complex features including manganese charge ordering, structural modulation, and widespread stacking faults.
The insight gained from this part of the project allows for a better understanding of the correlation between the structure and magnetic properties of birnessite-type materials. The current research contributes to the understanding of these deceptively complex compounds and should stimulate further studies into a potential new class of 2D magnetic materials.
3. The magnetic behavior of the geometrically frustrated compound K3CrO4 was explored for the first time. This complex oxide is a 3d1 system (S = ½) with the unusual 5+ oxidation state of chromium. The crystal structure, static and dynamic magnetic properties of the compound were investigated in detail. The presence of several magnetic phase transitions was found on cooling, involving the appearance of canted antiferromagnetic order followed by the onset of cluster glass behavior below the freezing temperature. Further field-induced, temperature-dependent transitions were found at lower temperatures of 3-10 K.
The candidate further developed her synthetic skills by working with air/moisture-sensitive compounds and growing single crystals by different methods. She has carried out measurements of various physical-chemical properties, such as powder and single-crystal XRD, thermal analysis: TGA-DSC; investigation of magnetic properties: DC/AC magnetic susceptibility, magnetization vs field, magnetization decay measurements, and has also performed microscopy and spectroscopy analysis: SEM, EDS, EBSD, TEM, XPS. She became familiar with structure determination/modeling software packages such as GSAS, Jana, Diamond, APEX3, and SHELXL.
