Solvothermal synthesis of MnF2 nanocrystals and the first-principle study of its electronic structure

MnF2 nanocrystals were prepared by a solvothermal method. Its powder X-ray diffraction (XRD) pattern was indexed to the rutile-type structure with lattice constant a=4.857 and c=3.309 Å. The as-prepared MnF2 nanocrystals were spherical particles with a size of 40–60 nm by scanning electron microscopy analysis. Its optical absorption spectrum exhibited absorption features of Mn2+d−d transitions. The magnetic characterization indicated that the nanocrystals have antiferromagnetic–paramagnetic phase transition at 70.1 K and linear magnetization behavior at 2 K. The electronic structure of tetragonal MnF2 was studied by spin-polarized first-principle density-functional calculation with general gradient approximation (GGA) and pseudopotential localized basis sets, which shows that rutile-type MnF2 should be a three-dimensional paramagnetic insulator. Density of states (DOS) analyses indicate that the manganese 3d orbitals with α and β spin characters dominate the highest valence and lowest conduction bands, respectively. According to the calculated band structure, the optical absorption properties are attributed to d−d transition of the manganese ions. The agreement between simulated and observed absorption spectrum was obtained, which confirms that the present calculated results provide a reasonable description of the electronic structure of rutile-type MnF2.