Multiferroic properties and magnetoelectric coupling observed in nanocrystalline HoFeO3

Abstract

Nanocrystalline holmium orthoferrite (HoFeO3) was synthesized by the chemical sol-gel technique. The main focus of attention was to explore the behavior of nanocrystalline system of HoFeO3 in the context of multiferroicity. Structural investigation by observing X-ray diffractograms and its thorough Rietveld analysis was carried out in detail which confirms the deviation in crystallographic structure. Structural study confirms the pure orthorhombic (Pnma) phase of HoFeO3 with zero impurity including the presence of uniform particle size distribution in the nano regime. Different useful structural parameters were also calculated from this theoretically generated pattern, which help to understand the magnetoelectric behavior explored in the sample. Surface morphology studied by FESEM micrographs confirmed a more or less uniform grain distribution in nano regime. EDAX spectra and mapping confirms the elemental purity. Thermal variation of magnetization measurements of HoFeO3 was carried out under zero-field cooled and field (~200 Oe) cooled conditions. Also, variation of magnetization with field (MH Loop) yields the presence of magnetic ordering with a relatively high value of magnetization compared to its corresponding bulk counterpart. During field-variation, magnetization value wasn’t yet saturated even at the maximum applied field of ~3 T, indicating the presence of magnetic ordering and superparamagnetism. Detailed high-temperature dielectric study including thermal variation, as well as frequency variation of dielectric constant together with related electric parameters provide various important information like ferro to para transition temperature, etc. These observations and various analyzes including Cole-Cole analysis of frequency variation of permittivity, Nyquist plot impedance analysis, etc. provide all dielectric parameters which are essential to understand the dielectric properties of the sample. The studies of ferroelectric loop and presence of room temperature magnetoelectric coupling suggest type-II multiferroicity of the present system of HoFeO3, which is usually not found in the bulk system. Presence of prominent remnant polarization with feeble dielectric loss and substantial magnetization clearly establishes the multiferroic candidature of nanocrystalline HoFeO3. This signature of multiferroicity will definitely strengthen the quality of application of the sample in M-E devices.