arXiv subjects

Maxim Molokeev

Publications and source records attributed to Maxim Molokeev.

3 recordsLinked to original sources

arXiv2026

Unraveling the Origin of Ferrimagnetic Signatures in (Fe,Mn,Ga)2O3 Bixbyites: The Role of Structurally-Undetectable Spinel Impurities

The cubic Fe2-xMnxO3 is an intriguing material that has recently been investigated for various applications, including lithium-ion battery anodes, catalysts, energy storage media, humidity sensors, and photocatalysts. Despite its wide range of promising applications, the magnetic properties of Fe2-xMnxO3 remain controversial, with different sources reporting conflicting information regarding the type of magnetic ordering, phase transition temperature, and magnetic moment of this compound. This work presents a study of the magnetic state of three Fe2-xMnxO3:Ga solid solutions with varying Mn:Fe:Ga ratios, along with one gallium-free Fe2-xMnxO3 reference sample. We performed a detailed analysis of the actual chemical composition and crystal structure of the synthesized samples using energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS) to evaluate compositional differences. The magnetic states of the three Fe2-xMnxO3:Ga samples and the gallium-free Fe2-xMnxO3 were investigated using magnetometry and Mossbauer spectroscopy. The low-temperature magnetic anomalies were found to be more consistent with spin-glass-like freezing than with conventional long-range antiferromagnetic ordering. Although variations in magnetic behavior were observed and found to depend on composition and the cooling rate during synthesis, our results demonstrate that these factors do not account for the drastically different magnetic properties reported for similar bixbyite-type oxides. Instead, the apparent room-temperature ferrimagnetism observed in one sample is most likely extrinsic and can be attributed to a trace spinel-type impurity phase, as supported by magnetizations and ESR measurements. Thus, the origin of these discrepancies lies primarily in the chemical purity of the samples and, to a significant extent, in the synthesis technique employed.

cond-mat.mtrl-sci↗

arXiv2021

Anisotropic thermal expansion and electronic transitions in the Co$_3$BO$_5$ ludwigite

The investigations of the crystal structure, magnetic and electronic properties of the Co$_3$BO$_5$ at high temperatures were carried out using powder x-ray diffraction, magnetic susceptibility, electrical resistivity, and thermopower measurements. The orthorhombic symmetry (Sp.gr. Pbam) was established at 300 K and no evidence of structural phase transitions was found up to 1000 K. The thermal expansion of the crystal lattice is strongly anisotropic. At $T<T_c=550$ K, a large thermal expansion along the c-axis is observed with simultaneous contraction along a-axis. The activation energy of the conductivity decreases significantly at high temperatures and follows the thermal expansion variation, that exhibits two electronic transitions at ~500 and ~700 K, in coincidence with the anomalies of the heat capacity. Electronic transport was found to be a dominant conduction mechanism in the entire temperature range. The temperature dependence of the effective magnetic moment reflects the evolution of the spin state of Co$^{3+}$ ions towards the spin crossover to a high spin state. The interrelation between the crystal structure and electronic properties is discussed.

cond-mat.mtrl-sci↗

arXiv2015

Structural and Magnetic Characterization of Ni2MnBO5 ludwigite

Single crystals of ludwigite Ni2MnBO5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition is differ from the content of the initial Mn2O3 - CuO components of flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed strong antiferromagnetic interactions and appearance of magnetic ordering phase at the temperature T=85 K. The hypothesis of the existence of several magnetic subsystems was supposed.

cond-mat.mtrl-sci↗