A. A. Selyutin

Low-temperature nonlinear effects in the conductivity of lightly doped cuprates La2−xSrxCuO4 in antiferromagnetic state

Low-temperature conductivity of antiferromagnetic cuprates La2−xSrxCuO4 prepared by solid-phase synthesis was investigated. The concentration of strontium in the samples was 0.01, 0.005 and 0.001. In the temperature range T TN (where TN is the Neel temperature) a transition to the metallic type of conductivity was observed. Nonlinear effects in low-temperature conductivity, magnetoresistivity, as well as current-controlled negative differential resistance were found. It was established that the nonlinear behavior of conductivity intensified with decreasing the strontium concentration. For temperatures T < 10 K, the effect of positive magnetoresistance was observed. It is suggested that this effect can be attributed to the presence of a new low-temperature magnetic phase (spin density waves).

Resistive properties of La2 − xSrxCuO4 low-dopped cuprates in the antiferromagnetic state at low temperatures

The nonlinear dependence of conductivity and negative differential resistance of ceramic samples of La2 − xSrxCuO4 in the antiferromagnetic state is revealed. The possible influence of a spatially inhomoge-neous distribution of strontium impurities on the low-temperature behavior of conductivity is discussed.

The spin state of manganese atoms in Sr2MnSbO6 complex oxides

The magnetic susceptibility of Sr2MnSbO6 solid solutions in a Sr2AlSbO6 diamagnetic diluent is investigated. Variation in the magnetic characteristics with temperature and the solution concentration indicates the coexistence of two spin states of manganese atoms: low-spin and high-spin. The possibility of spin transitions is due to temperature-dependent local distortions in the crystal structure of the solutions.

Features of exchange interactions in double perovskites

Magnetic susceptibility of double perovskites Sr2BB′O6 (B = Sc, Fe, Cr; B′ = Sb, Nb, W) and their dilute solid solutions has been studied. The complex changes of Sr2BB′O6 magnetic properties have revealed temperature-dependent distortions of crystalline structure and local ordering of 3d elements atoms in different spin states.

Character of ordering of nickel atoms in LiMO2

The state of nickel atoms in the solid solutions based on LiScO2 and LiGaO2 has been investigated. It is established that the anomalies of magnetic characteristics can be explained by only the presence of stable clusters, containing Ni(III) atoms in two (high and low) spin states. The cluster stability is independent of the crystallographic environment of the nickel atoms replacing the scandium and gallium ones.

Magnetoresistive properties of cold-pressed CrO2 powder, prepared by hydrothermal synthesis

The resistive, magnetoresistive and magnetic properties of cold-pressed CrO2, powder prepared by hydrothermal synthesis from chromic anhydride have been studied. The powder particles (with a mean diameter of about 120 nm) were nearly spherical. The particles stabilized with a β-CrOOH surface layer. The powder compact (with a Curie temperature of about 385 K) revealed nonmetallic temperature behavior of the resistance (with an R(T) dependence close to exponential at T < 20 K). A giant negative magnetoresistance (MR) (∼20% at T ≈ 5K) is found. MR decreased rapidly with an increase in temperature (to 0.3% at T > 200 K). Such MR behavior is shown to be typical of a system of magnetic grains with magnetic (spin-dependent) tunneling.

The role of local environment in charge ordering of perovskite-like oxides

The properties of magnetically diluted perovskite-like complex oxides La2 − xAxMO4 (M is Fe or Mn and A is Sr or Ba) have been studied. Charge and spin ordering is suggested to be interrelated with the local structural characteristics and the electronic structure of nanoclusters of transition elements found in the ceramics studied.

Geometric frustrations in magnetically diluted complex oxides LiMO2 (M = Sc, Ga, 3d elements)

The effect of local environment of a transition-element atom on the properties of bulk ceramics has been investigated by the example of complex oxides LiMO2 (M = Sc, Ga, Fe, Co, Ni). It is found that the anomalies in the magnetic properties of all systems studied are due to the presence of nanoclusters of transition-element atoms and the magnetic and geometric frustrations related to the nanocluster formation.