Ground state formation in a strong hubbard correlation regime in iron monosilicide

Low-temperature anomalies in the physical properties of iron monosilicide are analyzed based on the results of thorough measurements of the conductivity, Hall coefficients, thermo emf, and magnetic characteristics of high-quality single-crystal FeSi samples at liquid helium (LHe) and intermediate temperatures. It is demonstrated that the most adequate and consistent interpretation of the experimental magnetic, transport, and optical characteristics can be given within the framework of the Hubbard model. The model parameters are determined and the arguments are presented which provide evidence of the spin polaron formation and the density of state (DOS) renormalization taking place in FeSi in the vicinity of the Fermi energy at intermediate temperatures. It was found that a decrease in the sample temperature in the region of T < T _c ≈ 15 K is accompanied by a transition to a coherent regime of the spin density fluctuations. As a result, the ferro-magnetic character of the interaction leads to the formation of magnetic microdomains with a characteristic size ～10 Å. The exchange-induced magnetization enhancement in the vicinity of charge carriers in these microdomains probably accounts for the anomalous components in the Hall coefficient and the magnetization hysteresis observed in FeSi at LHe temperatures. The nature of the low-temperature transition at T _m ≈ 7 K in the system of interacting magnetic microparticles in iron monosilicide is discussed.     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.     

Hopping conductivity of carbynes modified under high pressures and temperatures: Galvanomagnetic and thermoelectric properties

The conductivity, thermopower, and magnetoresistance of carbynes structurally modified by heating under a high pressure are investigated in the temperature range 1.8–300 K in a magnetic field up to 70 kOe. It is shown that an increase in the synthesis temperature under pressure leads to a transition from 1D hopping conductivity to 2D and then to 3D hopping conductivity. An analysis of transport data at T ≤ 40 K makes it possible to determine the localization radius a ～ (56?140) Å of the wave function and to estimate the density of localized states _g(E _F) for various dimensions d of space: _g(E _F) ≈ 5.8 × 10⁷ eV^?1 cm^?1 (d=1), _g(E _F) ≈5×10¹⁴ eV^?1 cm ^?2 (d=2), and _g(E _F)≈1.1×10²¹ eV^?1 cm_?3 (d=3). A model for hopping conductivity and structure of carbynes is proposed on the basis of clusterization of sp ² bonds in the carbyne matrix on the nanometer scale.     

Disordering in Pyridine at High Pressures

JETP Letters - Pyridine has recently attracted significant attention because of its polymorphism and capability to form polymerized hydrocarbons at high pressures that have great technological...     

A new nanocluster carbyne-based material synthesized under high pressure

The DC and AC conductivities and the magnetoresistance and thermopower of carbyne samples were studied over the temperature range 1.8–300 K at frequencies 10 MHz–1 GHz. It was established that a variation in the fraction of sp ² bonds in carbynes induces a transition from one-to two-and then to three-dimensional conduction. The physical properties of the new carbyne-based solids may be understood within the model treating carbyne as a nanocluster material based on linear carbon chains and having a characteristic cluster size of 1 to 10 nm.     

Ferromagnetism in the high-pressure phases of (GaSb)1−x Mnx

The electrophysical and magnetic properties of recently discovered high-pressure phases in the GaSb-Mn system with simple cubic and tetragonal structures have been examined. It has been shown that samples with the primitive cubic structure for low temperatures are in the ferromagnetic state and the Curic temperature depends on the initial manganese content and reaches T _c = 280 K for x = 0.6. It has been shown that these samples for a manganese content x ≤ 0.5 are in the semiconducting state with large impurity conduction and pass to the metallic state as x increases. The GaSbMn phase with the tetragonal structure has ferromagnetic properties up to temperatures of T ～450 K (at which the phase begins to decay) and exhibits metallic properties. The magnetization at T = 77.3 K is equal to M = 0.58 μ_B and 0.28 μ_B per manganese ion for the simple cubic and tetragonal phases, respectively.     

Electrotransport and magnetic properties of Cr-GaSb phases synthesized under high pressure

The electrotransport and magnetic properties of new phases in the Cr-GaSb system were studied. The samples were prepared by high-pressure (P=6-8 GPa), high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy. One of the CrGa(2)Sb(2) phases with an orthorhombic structure Iba2 has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications. Another high-temperature phase is paramagnetic and identified as tetragonal I4/mcm.     

AsS melt under pressure: one substance, three liquids

An in situ high-temperature--high-pressure study of liquid chalcogenide AsS by x-ray diffraction, resistivity measurements, and quenching from melt is presented. The obtained data provide direct evidence for the existence in the melt under compression of two transformations: one is from a moderate-viscosity molecular liquid to a high-viscosity nonmetallic polymerized liquid at P approximately 1.6-2.2 GPa; the other is from the latter to a low-viscosity metallic liquid at P approximately 4.6-4.8 GPa. Upon rapid cooling, molecular and metallic liquids crystallize to normal and high-pressure phases, respectively, while a polymerized liquid is easily quenched to a new AsS glass. General aspects of multiple phase transitions in liquid AsS, including relations to the phase diagram of the respective crystalline, are discussed.