Study of the Brownian Broadening in the Mössbauer Spectra of Magnetic Nanoparticles in Colloids with Different Viscosities

Response to Comment on Oil-Dispersed α-Fe2O3 Nanoparticles as a Catalyst for Improving Heavy Oil Oxidation

“…It is generally accepted that IS, QS, and HF are the main parameters for phase analysis in Mössbauer spectroscopy. The line width cannot be such a good fingerprint indicator, because the line width for the same phase depends upon many factors, such as instrumental broadening, the effect of the sample thickness, diffuse broadening, the effect of the particle size, the uniformity of the local environment of the Mössbauer atom (defects, impurities, crystallinity, and others), various relaxation effects associated with fluctuations of electric and magnetic fields on the nucleus, etc. This is probably why the Mössbauer Mineral Handbook , published by the Mössbauer Effect Data Center, contains only data on the temperature, isomer shift, quadrupole splitting, and hyperfine magnetic field.…”

Effects of Macromolecular Crowding on Nanoparticle Diffusion: New Insights from Mössbauer Spectroscopy

“…In this work, we propose another approach based on Mössbauer spectroscopy to study the nanoscale diffusion and HD properties of iron-containing NPs, which are widely used in various fields of biomedicine, such as drug delivery, MRI, and hyperthermia. , Recently, we extended the model to analyze the hyperfine structure of Mössbauer spectra to study NP diffusion motion and demonstrated the applicability of such an approach for iron-containing NPs of various sizes . A hallmark of such measurements is that Mössbauer spectroscopy is sensitive to only 57 Fe nuclei, which makes it possible to obtain the NP self-diffusion coefficient in media of any complexity, regardless of the solution transparency, the concentration of the constituents, or the type of crowding agent.…”

“…To assess this, we analyzed the hyperfine structure of Mössbauer absorption spectra of both CFN dry powder and CFNs dispersed in BSA/glycerol solutions (Figure ). Figure (top) shows that the hyperfine structure of the absorption spectrum of dry CFNs looks like a superposition of a well-resolved Zeeman asymmetric line sextet, which is a characteristic of ferrimagnetic NPs, and a minor quadrupolar doublet, which can be attributed to the very small NPs . Due to the ferrimagnetic nature of cobalt ferrite, the absorption spectrum was treated within the model of the magnetic dynamics of an ensemble of ferrimagnetic NPs in the two-sublattice approximation. , In this model, each ferrimagnetic particle of an ensemble is characterized by the simplest expression for its energy density: where J is the positive exchange coupling constant, M 1 and M 2 are the sublattice magnetizations, K is the axial magnetic anisotropy constant, and θ 1 and θ 2 are the angles between vectors M 1 and M 2 and the easiest magnetization axis, respectively.…”

“…Then, the phenomenological consideration can be performed with the assumption that the magnetic moment of each i th sublattice precesses in the internal effective field: whereas the equations of motion for the sublattice magnetizations can be expressed in the form where γ i is the magneto-mechanical ratio for the i th sublattice. Solving these equations, one can deduce the excitation spectrum of the ensemble of ferrimagnetic particles, which represents four excitation branches corresponding to the normal modes of self-consistent regular precession of sublattice magnetizations and the continuous spectrum of nutations of magnetizations accompanying these normal modes. , The equilibrium state of the ensemble of particles at a given temperature T is described by the Gibbs distribution over the “quasi-stationary” states, i.e., precession and nutation trajectories of vectors M 1 and M 2 with given values of the integral of motions, the energy E , and the reduced total magnetic moment m : where V is the volume of particles and C is the normalization constant. Each of the “quasi-stationary” states is characterized by the average values of the longitudinal components of reduced sublattice magnetizations m ̅ 1 z ( E , m ) and m ̅ 2 z ( E , m ).…”

“…The type of spectral transformation was similar for all CFN-containing liquid samples, regardless of the BSA content. To correctly evaluate the diffusion line broadening ΔΓ, we have performed the simultaneous fitting of each pair of Mössbauer spectra of CFN dry powder and CFNs in liquids measured at the same temperature according to the previously described procedure . The spectral line width is an integral parameter and can be evaluated from fitting with a good accuracy (in our case, a few percent).…”