Preparation and magnetic and microwave absorption properties of MnNb2O6 ellipsoid-like hierarchical structures

Great efforts have been made to synthesize columbite niobates due to their fascinating properties and applications. In this research, ellipsoidal MnNb2O6 crystals have been successfully prepared by a facile hydrothermal method. X-ray powder diffraction patterns showed that the products have the typical orthorhombic columbite structure. Electron microscopy analysis revealed that the obtained MnNb2O6 ellipsoids had a very rough surface, with flaky hierarchical structures composed of nanoparticles with diameters of 10-20 nm. Based on time-dependent experiments, a possible growth mechanism of the ellipsoidal hierarchitectures was also proposed. The magnetization studies demonstrate that the products exhibit antiferromagnetic behavior with a Neel temperature of about 4 K. The microwave absorption properties of the ellipsoidal MnNb2O6 hierarchical structures were also investigated with a vector network analyzer. The absorption peak position moves to a lower frequency with increasing thickness of the sample. The value of the minimum reflection loss is -11.6 dB at 7.8 GHz with a thickness of 3.5 mm, and a reflection loss lower than -10 dB can be obtained in the frequency range of 7.2-8.3 GHz.