Influence of structural defects and crystallite size on physical properties of Yb₃Fe₅O₁₂

Abstract

This paper was the first to present the results of studying the influence of structural defects on the physical properties of pre-synthesized ytterbium iron garnet (YbIG). The concentration and type of structural defects were controlled by mechanically activating the powders using Bridgman anvils. Using scanning electron microscopy and X-ray diffraction (XRD), it was revealed that the particle morphology, the unit cell parameters, mean size of the coherent scattering regions ($D$) and microstrains ($\Delta d/d$) vary in a wide range. Using optical spectroscopy, XRD and FTIR to study the dynamic properties of the crystal lattice, showing that the bandgap and force constants of dodecahedral-coordinated ytterbium (Yb–O)_d and octahedral-coordinated iron (Fe–O)_o change non-monotonically with decreasing crystallite size. By analyzing the dependence of the magnetic hysteresis loop $M(H)$ on the crystallite size $D$, it was concluded that there was a critical crystallite size (${D}_{\mathrm{crit}}=75$ nm) of YbIG, at which the coercive force ${H}_{\mathrm{c}}$ has a maximum value. For the first time, changes in g-factor and the half-width $\Delta H$ of the electron paramagnetic resonance (EPR) spectra of nanoscale crystallites were found to be correlated with the parameters of the magnetic hysteresis loop $M(H)$.