Temperature-dependence measurements specific heat, thermoelectric power, conductivity, and electron paramagnetic resonance measurements were performed on Mn_0.75Co_2.25BO₅ powder at temperatures above 290 K. Single crystals of Mn_0.75Co_2.25BO₅ were grown by the flux method using Bi₂Mo₃O₁₂-based solvent diluted with Na₂CO₃. To investigate EPR and specific heat capacity, the single crystals were ground to powder. The temperature dependencies of the resistance, specific heat, Seebeck constant, and EPR spectra in the range from 290K to 700K were obtained. The transition from the dielectric state to the semiconductor state was detected at 348 K, consistent with the change in the fine structure of the EPR spectrum associated with S = 5/2 for the manganese ion Mn²⁺.

In the temperature range T = 5−80 K, the CW X-band EPR method was used to study blood and its serum samples taken from professional athletes, patients with connective tissue dysplasia and volunteers from the control group. At the measurement temperature of 5 K, a fairly intense absorption line with an effective g-factor of ≈ 5.84 was recorded in almost all EPR spectra of blood serum, the intensity of which decreases with increasing temperature. At temperatures above 40 K, this signal is not recorded. We believe that this absorption line arises from high-spin Fe³⁺ ions bound to the second conformation of the transferrin N-lobe iron site with E/D ≤ 0.1. Simulation of the X-band EPR spectrum of serum recorded in the range of 500−2500G at 5K using the EasySpin software package, in particular the “pepper” utility, allowed us to describe well all the features of the experimental spectrum from human transferrin: a double peak, a shoulder, wide wings of the signal with g′ ∼ 4.3; a weak line with g′ ∼ 9.0 and, most importantly, a signal with g′ ≈ 5.84.

The circumstances that contributed to the discovery of the EPR phenomenon by E.K. Zavoisky are analyzed. The emphasis is made on the applying of magnetic field modulation

High-entropy oxide Mg_0.2Co_0.2Fe_0.2Ni_0.2Zn_0.2O was successfully synthesized. Using X-ray diffraction analysis, it was found that the sample has a single-phase composition with the NaCl-type face-centered cubic structure and the lattice constant of 4.22 Å. The sample was studied using Mössbauer spectroscopy at temperatures from 80 K to 295 K. It was determined that the relative content of divalent and trivalent iron ions in the sample is 67% and 33%, respectively. Based on the temperature dependence of the hyperfine magnetic field on ⁵⁷Fe nuclei, the magnetic transition temperature was determined to be 201 K.