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The effects of substitution of barium by tin on the phase composition, structural imperfection, and properties of lanthanum manganite perovskites La0.7Ba0.3−xSnxMnO3 (x=0, 0.1, 0.15, 0.2, 0.3) are established by comprehensive studies done by x-ray diffraction, resistive, and magnetic (including NMR on 55Mn and 139La) methods. It is shown that the introduction of Sn leads to the formation of a pyrochloric phase La2Sn2O7, to an increase in the density of lattice defects of the manganese-enriched main lanthanum manganite phase, and to a substantial decrease of the magnetoresistive effect. The smearing of the metal–semiconductor phase transition temperature is explained by an increase in the inhomogeneity and imperfection of the perovskite structure. The low activation energy is confirmed by a high degree of inhomogeneity and imperfection of the crystal lattice of the samples studied. The broad, asymmetric NMR spectra of 55Mn and 139La attest to high-frequency electron exchange between Mn3+ and Mn4+ and noneq...

A study is made of the external structure, magnetization, and magnetoresistive effect in ceramic samples of (La0.8Sr0.2)1−xMn1+xO3 annealed at 1150 and 1500 °C. It is shown that the additional annealing at 1500 °C leads to significant changes in the magnetization and increases the magnetoresistive effect by a factor of 2–3, depending on x. An “anomalous” magnetic hysteresis is observed on the initial parts of the magnetization curves in both ceramic and laser-deposited film samples. It is found that the value of the “anomalous” magnetic hysteresis depends on the composition of the samples (on x) and their annealing temperature. A mechanism for the appearance of the “anomalous” hysteresis is proposed, involving the presence and interaction of ferromagnetic and antiferromagnetic phases.

The La 0.6 Sr 0.2 Mn 1.2− x Cr x O 3 (0⩽ x ⩽0.2) ceramic samples with perovskite-like structure (R 3 c) have been studied using the X-ray diffraction, NMR, magnetic and resistance methods. The 55 Mn NMR spectrum was shown to depend strongly on the Cr/Mn ratio. A single symmetric line centered at 379 MHz was found for La 0.6 Sr 0.2 Mn 1.2 O 3 ( x =0). For La 0.6 Sr 0.2 Mn 1.1 Cr 0.1 O 3 , the 55 Mn NMR spectrum is slightly expanded and shifted to lower frequencies. An analysis of the 55 Mn NMR spectrum for the La 0.6 Sr 0.2 MnCr 0.2 O 3 compound has shown that a wide asymmetrical line can be uniquely expanded into four components with different resonance frequencies. These components arise due to both different ionization states of the manganese ions and a non-equivalence of their crystallographic surrounding. There are manganese ions, whose ionization states are close to (3+) and (4+), as well as Mn ions with intermediate valence which resulted from the high-frequency electron exchange. The Curie temperature and the temperatures of both resistance maximum and magnetoresistance peak were found to decrease, while the value of magnetoresistance increases with increasing Cr content.

We have observed an anomalous magnetic hysteresis in polycrystalline (ceramic) and single crystal (film) samples of La0.6Sr0.2Mn1.2O3−δ manganites with a perovskite structure. The anomaly is explained by the coexistence and interaction of two magnetic phases (ferromagnetic and antiferromagnetic) in these lanthanumcontaining manganites.

A 2+ Mn 4+ O 3 (A-Ni, Co, Mg, Cu) manganates with ilmenite structure have been obtained by solid phase synthesis at high pressure and temperature. The synthesis conditions for single phase samples have been determined, and investigations of the magnetic, electric, magnetooptic, and resonance properties were carried out

Magnetic and structural characteristics of ErFeO3, TmFeO3, and YbFeO3 single crystals were studied over a wide temperature range. Magnetic measurements found that the spin-rotation transitions in all crystals are well described by the earlier proposed theory with no fitting parameters. Additionally, they have shown the absence of the magnetic compensation point in TmFeO3 and a noticeable growth of the c-axis magnetization at low temperatures in TmFeO3 and ErFeO3. The x-ray measurements found no symmetry-lowering lattice distortions during the reorientation. Overall, the measurements cover a wide range of material parameters and demonstrate the generality of the modified mean field theory of the Γ4→Γ24→Γ2 orientation phase transitions in orthoferrites.

It is theoretically shown and experimentally found that in the TbFe1−xAlxO3 system the presence of non-magnetic ions Al3+ (magnetic vacancies) results in a considerable increase of anisotropy energy in the ac-plane and suppresses the spontaneous orientational transition Γ42 Γ2, observed in pure TbFeO3. The character of the orientational transition Γ42 Γ2 induced by the applied field H along the a-axis is studied. The Hx−T phase diagram contains a tricritical point. A qualitative change of the temperature dependence of magnetization and susceptibility along the c-axis is found in TbFe1−xAlxO3 as compared to TbFeO3. This is explained by the deviation of the Ising axes of Tb3+ ions from the ab-plane of the crystal. It is experimentally shown that the magnetic vacancies suppress the antiferromagnetic ordering of the terbium ions. [Russian Text Ignored].

An investigation is made of magnetic, magnetoelastic, and elastic properties of erbium orthoferrite in the region of the phase transitions. The first and the second magnetoelastic constants of this orthoferrite, and the first and the second anisotropy constants of the iron sublattice are determined. It is shown that the compensation point in the field H ‖ σ0 is the first-order phase transition. On the basis of magnetization and Young's modulus measurements, and also from symmetry considerations it is concluded that in the temperature range 2 to 4 K Γ12 is the magnetic structure of ErFeO3. [Russian Text Ignored]

Etude de l'aimantation en fonction de la temperature (1,8 a 300 K) sous un champ magnetique jusqu'a 2,6×10 6 A/m