Quantum critical point and spin fluctuations in lower-mantle ferropericlase

Effect of Doping on the Electronic Structure of the Earth’s Lower Mantle Compounds: FeXO3 with X = C, Al, Si

The effect of the mutual doping of C, Si, and Al atoms on the electronic structure and magnetic properties of FeXO₃ (X = C, Al, Si) compounds, which are constituent compounds of the Earth’s lower mantle, was studied. In our first principles calculations, it was found that doping with carbon for both FeSiO₃ and FeAlO₃ leads to the transition of the compound from a half-metallic state to a metallic one. The values of the magnetic moments of Fe were obtained for pure and doped compounds. For the doped compounds, there is a tendency of the Fe magnetic moment to increase with the growth in the number of substituted ions in the case of replacing Si with C and Si for Al; on the contrary, in the case of replacing Al with C and Si, a decrease in the magnetic moment was revealed. For FeXO₃ (X = C, Al, Si), the obtained magnetic moment values were found to be in a good agreement with the known experimental data.

Effect of Multiplicity Fluctuation in Cobalt Ions on Crystal Structure, Magnetic and Electrical Properties of NdCoO3 and SmCoO3

The structural, magnetic, electrical, and dilatation properties of the rare-earth NdCoO₃ and SmCoO₃ cobaltites were investigated. Their comparative analysis was carried out and the effect of multiplicity fluctuations on physical properties of the studied cobaltites was considered. Correlations between the spin state change of cobalt ions and the temperature dependence anomalies of the lattice parameters, magnetic susceptibility, volume thermal expansion coefficient, and electrical resistance have been revealed. A comparison of the results with well-studied GdCoO₃ allows one to single out both the general tendencies inherent in all rare-earth cobaltites taking into account the lanthanide contraction and peculiar properties of the samples containing Nd and Sm.

Investigation of iron spin crossover pressure in Fe-bearing MgO using hybrid functional

Pressure-induced spin crossover behaviors of Fe-bearing MgO were widely investigated by using an LDA  +  U functional for describing the strongly correlated Fe-O bonding. Moreover, the simulated spin crossover pressures depend on the applied U values, which are sensitive to environments and parameters. In this work, the spin crossover pressures of (Mg_1-x ,Fe _x )O are investigated by using the hybrid functional with a uniform parameter. Our results indicate that the spin crossover pressures increase with increasing iron concentration. For example, the spin crossover pressure of (Mg_0.03125,Fe_0.96875)O and FeO was 56 GPa and 127 GPa, respectively. The calculated crossover pressures agreed well with the experimental observations. Therefore, the hybrid functional should be an effective method for describing the pressure-induced spin crossover behaviors in transition metal oxides.

Mechanism of magnetic moment collapse under pressure in ferropericlase

We propose a new scenario for the magnetic collapse under pressure in ferropericlase (FP) (Fe(1/4)Mg(3/4))O without the presence of intermediate spin state, which contradicts the mechanism proposed in (2013 Phys. Rev. B 87 165113). This scenario is supported by results of combined local density approximation + dynamical mean-field theory method calculations for the paramagnetic phase at ambient and high pressures. At ambient pressure, calculation gave (Fe(1/4)Mg(3/4))O as an insulator with Fe 3d-shell in high-spin state. Experimentally observed high-spin to low-spin state transition of the Fe(2+) ion in the pressure range of 35-75 GPa is successfully reproduced in our calculations. The spin crossover is characterized by coexistence of Fe(2+) ions in high and low spin state but intermediate spin state is absent in the whole pressure range. Moreover, the probability of Fe ion d(7) onfiguration with S = 1 grows with pressure due to shortening of metal-oxygen distance. Also, no metal-insulator transition was obtained up to the pressure 140 GPa in agreement with experiment.

Spin crossover in ferropericlase from first-principles molecular dynamics

Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of Earth's lower mantle. With increasing pressure, the Fe ions in the material begin to collapse from a magnetic to nonmagnetic spin state. We present a finite-temperature first-principles phase diagram of this spin crossover, finding a broad pressure range with coexisting magnetic and nonmagnetic ions due to favorable enthalpy of mixing of the two. Furthermore, we find the electrical conductivity of the mineral to reach semimetallic values inside Earth.