Morphology, structure and magnetic behavior of orthorhombic and hexagonal HoFeO3 synthesized via solution combustion approach

Abstract Nanostructured HoFeO3 powders were obtained by solution combustion method at various glycine-nitrate ratios (G/N = 0.2, 0.4, ..., 1.4). According to X-ray powder diffractometry data, the presence of two modifications of HoFeO3 in the synthesized samples was established: orthorhombic (Pbnm) and hexagonal (P63/mmc). The crystallite size of the obtained compositions varies from 62±6 to 29±3 nm, depending on the G/N ratio. From magnetic structure studies, it was found that HoFeO3 obtained with a stoichiometric amount of glycine in the reaction solution is in the magnetically ordered state and is represented by a sextet with quadrupole splitting QS = 0 mm/s, isomeric shift IS = 0.36 mm/s and effective field strength Heff = 497 kOe. According to the results of vibrational magnetometry, it is found that the orthoferrites obtained have a ferromagnetic structure, the main parameters of which (Ms, Mr and Hc) systematically change with a change in the redox ratio of the reaction mixture and, as a consequence, their phase composition, and reach maximum values at a G/N ratio = 0.6. In the samples obtained with a significant excess and lack of glycine (G/N = 0.2 and 1.4), despite their amorphous nature, hysteresis loops characteristic of the ferromagnetic state of the substance are observed. It is hopeful to obtain a pure hexagonal modification of HoFeO3 via heat treatment amorphous products of glycine-nitrate combustion.