A. I. Tovstolytkin

Magnetic and magnetoresistive properties of sodium-substituted lanthanum manganites

The magnetic, electric, and magnetoresistive properties of bulk samples of La1−xNaxMnO3±δ (x=0.08–0.16) are studied. It is shown that at low temperatures all samples are ferromagnetic and the temperature of the transition from the paramagnetic into the ferromagnetic state increases with increasing sodium content. It is found that the saturation magnetization reaches its maximum value, close to that computed theoretically, in samples with x=0.12. A deviation of x from 0.12 decreases the saturation magnetization and broadens the magnetic transition. Analysis of the behavior of the magnetoresistance shows that there exists, together with the ferromagnetic conducting phase, a disordered weakly conducting phase, the volume fraction of the latter increasing as x deviates away from 0.12. The characteristic behavior of the magnetic and magnetoresistive properties of La1−xNaxMnO3±δ samples are tied to the particulars of the evolution of the chemical composition and defectiveness of the samples as a function of the...

Crystallographic, electrical, and magnetic properties of the system La0.7Sr0.3Mn1−xFexO3

On the basis of x-ray structural data and studies of the electrical, magnetic, and magnetoresistive properties and the ferromagnet resonance spectra of ceramic samples of La0.7Sr0.3Mn1−xFexO3 (0⩽x⩽0.10) it is established that a competition between structural changes influencing the ferromagnetism leads to a monotonic weakening of the ferromagnetism (a lowering of TC by around 5K∕%Fe). The increase of the magnetoresistance in the low-temperature region and the large values of the low-field contribution to the magnetoresistance are indicative of an inhomogeneous character of the electrical conductivity and magnetization of the samples at T<TC, which may be due to the coexistence of the ferro- and paramagnetic phases over a wide temperature region.

Structural, electrical, and magnetic properties of La0.7Ca0.3 − xNaxMnO3 ± γ solid solutions

AbstractLa0.7Ca0.3 − xNaxMnO3 ± γ (LCNM) solid solutions with x = 0, 0.04, 0.06, 0.08, and 0.10 have been synthesized (rhombohedral structure, sp. gr. R

Structural, electrical, and magnetic properties of La0.7Sr0.3Mn1−y CryO3

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Giant resistance switching effect in nano-scale twinned La0.65Ca0.35MnO3 film

c). Sodium volatility during sintering is shown to lead to the formation of vacancies on the lanthanum and oxygen sites. Ca2+ → Na+ substitution does not increase the fraction of Mn4+ in LCNM, but the increase in the concentration of lanthanum vacancies with increasing sodium content leads to an increase in ferromagnetic ordering temperature TC and magnetoresistance, which depend, in addition, on heat-treatment conditions on account of the sodium volatility.

Sol-gel synthesis and properties of tin-doped lanthanum manganites

The electric and magnetoresistive properties of partially crystallized (La,Na)MnO3 films near the paramagnet-ferromagnet transition are investigated. The objects of study are films obtained on polychore substrates by magnetotron sputtering and substrate temperatures 300 and 500°C. The temperature behavior of the electric resistance is analyzed to determine the limits of between the experimental data and the existing theoretical models. A generalized picture of the evolution of conduction mechanisms accompanying a change in temperature and regimes of heat treatment of the samples is constructed. It is shown that a correlation exists between the character of the temperature variation of the magnetoresistance and the change in the conduction mechanisms. The characteristic temperatures which describe the boundaries of the regions in which a definite conduction mechanism dominates are established.

Substrate effect on the properties of La0.775Sr0.225MnO3 films

Detailed structural data are presented for La0.7Sr0.3Mn1−yCryO3 solid solutions with 0 < y ≤ 0.10. Chromium substitution on the manganese site is shown to reduce the TC of the solid solutions at a rate of 4 K/mol % Cr. The 300-K magnetoresistance of La0.7Sr0.3Mn1−yCryO3 attains 8% in a field of 1.2 MA/m.

Effect of A-site vacancies on the magnetoresistive Effect in La1 − x − yCaxNayMnO3 ± δ

A study is made of the electrical properties of thin films of La0.775Sr0.225MnO3−δ prepared on single-crystal substrates of SrTiO3 by magnetron sputtering. A substantially nonlinear character of the current–voltage characteristic of the film samples is observed at temperatures below 270 K. It is shown that increasing the current density leads to a transition from a semiconducting to a metallic character of the conduction. An explanation of the results is proposed, based on the hypothesis of phase separation of the samples into conducting and insulating layers, stimulated by the mechanical stresses arising near the film–substrate boundary.