Electrical Resistance and Magnetoresistance of Cd3As2–30 mol % MnAs under High Pressures

Physics of the Solid State - The paper presents the results of a study on the Electrical resistance and magneto-resistance (MR) of the composite, consisting of a Dirac semimetal Cd3As2 and 30 mol %...     

Crystal structure of α‴-(Zn1−x Cd x )3As2 (x = 0.26)

Single crystals of the α?-phase of (Zn_{1 ? x} Cd _x )₃As₂ solid solution (x = 0.26) have been prepared and investigated by X-ray diffraction analysis. The tetragonal unit-cell parameters are found to be a = b = 8.5377(2) Å, c = 24.0666(9) Å, sp. gr. I4₁/amd, Z = 16. Zn and Cd atoms in the crystal statistically occupy three symmetrically independent positions in the mirror planes and are tetrahedrally coordinated by arsenic atoms. (Zn,Cd) tetrahedra share edges to form a three-dimensional structure framework. The α?-phase is geometrically related to the fluorite structure. The character of arrangement of tetrahedral vacancies in fluorite-like unit cells is revealed. Chains of tetrahedral vacancies form microchannels oriented parallel the a and b axes, which pierce the three-dimensional structure framework at different levels along the c axis. The structure of α″-Cd₃As₂ crystals is found to be similar to that of α?-(Zn_0.74Cd_0.26)₃As₂.     

Studying the dielectric, electromechanical, and elastic properties of K1 − x (NH4) x H2PO4 mixed crystals

Temperature dependences of the longitudinal permittivity, piezoelectric coefficient d ₃₆, and elastic constant c ₆₆ ^E of K_{1 ? x} (NH₄) _x H₂PO₄ mixed crystals are studied experimentally. A microscopic model is proposed for crystals of the K_{1 ? x} (NH₄) _x H₂PO₄ type that includes the piezoelectric contribution to the effective pseudospin cluster Hamiltonian. Dielectric elastic and electromechanical properties of these crystals with ammonium concentrations x below 0.40 are calculated in a wide temperature range using the cluster approach. The calculation results are in qualitative agreement with experimental data.     

Conductivity of La1−x CaxMnO3 under magnetic resonance of Mn ions

A change in the electrical conductivity, σ, is observed in the manganese perovskite La_1?x Ca_xMnO₃, with x=0 and 0.3 under saturation of the magnetic resonance transitions of Mn ions. This effect has a maximum in the temperature range of the magnetic phase transition of the compounds. Two contributions to the change in σ are found. The first, dominating in LaMnO₃, is an increase in σ caused by heating of the sample under magnetic resonance. The second is a σ decrease due to reorientation of the Mn spins, observed in La_0.7Ca_0.3MnO₃.     

Vapor-Phase Synthesis and Magnetoresistance of (Cd0.993Zn0.007)3As2 Single Crystals

JETP Letters - We report a highly anisotropic magnetoresistance of (Cd0.993Zn0.007)3As2 single crystals, which have been synthesized by the vapor-phase growth. Scanning electron microscopy and...     

Electric and Galvanomagnetic Properties of Cd3As2–20 mol % MnAs Composite under High Pressure

Physics of the Solid State - The pressure dependences of electrical resistance, Hall coefficient, charge carrier mobilities, and magnetoresistance of the Cd3As2–20 mol % MnAs composite are...     

The Synthesis and Investigation of the Electrical Properties of Tricadmium Diarsenide with MnAs Nanogranules

Technical Physics - Samples of tricadmium diarsenide with MnAs nanogranules (44.7 mol % MnAs) are synthesized. The morphology of the samples is studied by X-ray phase analysis and electron...     

Crystal structure and magnetic ordering of manganites La0.7Ca0.3Mn1 ? y Fe y O3

The influence of the replacement of Mn ions in the La_0.7Ca_0.3Mn_{1 − y} Fe _y O₃ compounds (0 ≤ y ≤ 0.09) by another transitional metal, Fe, was studied. The radii of both ions are almost identical, which makes the effect of the transitional metal on the physical properties of manganites more transparent. The crystal structure of three samples (with y = 0, 0.03, 0.09) is studied in the temperature range T = 1.5–300 K by neutron powder diffraction. All investigated samples belong to the orthorhombic space group Pnma (62). It is confirmed that Fe ions occupy the Mn positions in the unit cell. As the Fe concentration increases, the saturation value of the spontaneous magnetic moment and the Curie temperature decrease, but the ground state remains ferromagnetic for 0 ≤ y ≤ 0.1. The saturation values of the magnetic moments at T = 1.5 K are m _FM = 3.72(3), 3.40(3), and 3.27(3) μ _B /Mn for the samples with an Fe concentration y = 0, 0.03, and 0.09, respectively. Original Russian Text ? A.I. Kurbakov, V.S. Zakhvalinskii, R. Laiho, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 691–695.     

Thermoelectric Properties of a Ferromagnetic Semiconductor Based on a Dirac Semimetal (Cd<Subscript>3</Subscript>As<Subscript>2</Subscript>) under High Pressure

The pressure dependences of thermal emf (a parameter that ranks among the most sensitive to phase transformations) are studied for the purpose of identifying baric phase transitions in the 10–50 GPa interval in the Cd₃As₂ + MnAs (44.7% MnAs) structure formed by ferromagnetic MnAs granules in a semiconductor Cd₃As₂ matrix.     

Phase separation, ferromagnetism and magnetic irreversibility in La1−xSrxMn1−yFeyO3

Magnetic susceptibility, χ(T), is investigated in ceramic La_1−xSr_xMn_1−yFe_yO₃ (LSMFO) samples with x=0.3 and y=0.15−0.25. A ferromagnetic (FM) transition observed in LSMFO is accompanied with an appreciable decrease of the transition temperature with increasing y, which is connected to breaking of the FM double-exchange interaction by doping with Fe. Strong magnetic irreversibility, observed in low (B=10 G) field, gives evidence for frustration of the magnetic state of LSMFO. The FM transition, which is expanded with increasing B, is more pronounced in the samples with y=0.15-0.20 and broadens considerably at y=0.25, where the irreversibility is increased. Well above the transition, χ(T) exhibits a Curie-Weiss asymptotic behavior, yielding very large values of the effective Bohr magneton number per magnetic ion, incompatible with those of Mn or Fe single ions. At y=0.15 and 0.20 a critical behavior of χ⁻¹(T)∼(T/T_C−1)^γ in the region of the FM transition is characterized by influence of two different magnetic systems, a 3D percolative one with γ₌γ_p≈1.8 and T_C=T_C^(p), and a non-percolative 3D Heisenberg spin system, with γ=γ_H≈1.4 and T_C=T_C^(H), where T_C^(p)<T_C^(H). At y=0.25 the percolative contribution to the critical behavior of χ(T) is not observed. The dependence of χ on T and y gives evidence for phase separation, with onset already near the room temperature, leading to generation of nanosize FM particles in the paramagnetic host matrix of LSMFO. The ferromagnetism of LSMFO is attributable to percolation over the system of such particles and generation of large FM clusters, whereas the frustration is governed presumably by a system of smaller weakly-correlated magnetic units, which do not enter the percolative FM clusters.