A. V. Telegin

The influence of magnetic and electronic inhomogeneities on magnetotransmission and magnetoresistance of La0.67Sr0.33MnO3 films

The optical (absorption of light and magnetotransmission of IR radiation), magnetic, and transport properties of the epitaxial La0.67Sr0.33MnO3 films of different thickness grown by laser ablation on the (100) SrTiO3 and LaAlO3 substrates were investigated. The effect of magnetotransmission reaches 6% at the temperature of 350K while magnetoresistance reaches 7.6% at 354K in a magnetic field of 8kOe. The factors, which influence the values of magnetotransmission and magnetoresistance of manganite films, are discussed.

Giant magnetorefractive effect in La0.7Ca0.3MnO3 films

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

Giant magnetorefractive effect in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} films

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

Effect of isovalent doping of manganite (La1−xPrx)0.7Ca0.3MnO3 films (0≤x≤1) on their optical, magnetooptical, and transport properties near the metal-insulator transition

The optical, magnetooptical, and electric properties of epitaxial (La1−xPrx)0.7Ca0.3MnO3 films (0≤x≤1) grown by MOCVD on LaAlO3 and SrTiO3 substrates were studied. It is shown that the decrease in the average cation radius resulting from isovalent substitution of the Pr for La ions brings about a lowering of the Curie temperature, the metal-insulator transition temperature, and the temperatures of the maxima in magnetotransmission (MT) and magnetoresistance (MR). These temperatures depend only weakly on the substrate type. Substitution of La by Pr does not change the shape of the spectral response of the transverse Kerr effect. For concentrations x≤0.50, the maximum values of the Kerr effect and of the MT vary insignificantly, which should be assigned to the existence of a singly connected ferromagnetic metallic region at low temperatures. In films with x=0.75, the presence of ferromagnetic metallic drops in an antiferromagnetic insulating matrix was revealed. The totality of the experimental data obtained suggest that nanoscopic magnetic and electronic nonuniformities exist both in films with a singly connected metallic region and in an x=1 film, which is an antiferromagnetic insulator.

The evolution of magneto-transport and magneto-optical properties of thin La0.8Ag0.1MnO3+δ films possessing the in-plane variant structure as a function of the film thickness

Epitaxial La 0.8 Ag 0.1 MnO 3+δ films of different thicknesses (500-1000 nm) were grown on ZrO 2 (Y 2 O 3 ) substrates. Their optical, magneto-optical and transport properties were studied in order to clarify the effect of the epitaxial variant structure and Ag ion distribution on the conductivity, magnetoresistance and infrared magnetotransmission in these films. An original method was developed for separating MR contributions related to the colossal magnetoresistance near T C and the tunnelling magnetoresistance. It was established that in the La 0.8 Ag 0.1 MnO 3+δ films spin-polarization of electrons P reached ∼0.5. The transverse Kerr effect revealed the irregular distribution of Ag ions through the film thickness. The comparison of optical and electrical data implies lower silver content near the film-substrate boundary in relation to that in the domain volume.

IR radiation modulator based on the effect of magnetotransmission in lanthanum manganite operating near room temperature

A prototype of the IR radiation modulator operating at T=303 K, using the giant magnetotransmission effect in a La0.82Na0.18MnO3+δ lanthanum manganite film, has been constructed and the optical characteristics of the setup have been measured. In a wavelength range from 1.4 to 11 μm, the IR modulation depth varies from 3.5 to 6.5%. The possibilities of increasing the modulation depth are considered.

Magnetorefractive effect in La0.7Ca0.3MnO3 in the infrared spectral range

The reflection and magnetic reflection spectra, magnetic resistance, electrical properties, and equatorial Kerr effect in La0.7Ca0.3MnO3 crystals have been complexly investigated. The measurements have been performed in wide temperature and spectral ranges in magnetic fields up to 3.5 kOe. It has been found that magnetic reflection is a high-frequency response in the infrared spectral range to the colossal magnetore-sistance near the Curie temperature. Correlation between the field and temperature dependences of the magnetic reflection and colossal magnetoresistance has been revealed. The previously developed theory of the magnetorefractive effect for metallic systems makes it possible to explain the experimental data at the qualitative level. Both demerits of the theory of the magnetorefractive effect in application to the magnets and possible additional mechanisms responsible for the magnetic reflection are discussed.

Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

The magnetotransmission, magnetoreflection, and magnetoresistance of the La0.7Ca0.3MnO3 and La0.9Ag0.1MnO3 epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.

Optical and magneto-optical properties of nanostructured yttrium iron garnet

Bulk dense samples of nanostructured yttrium iron garnet Y3Fe5O12 with crystallite sizes of 20–40 nm are prepared by high-pressure torsion from a garnet powder with micron grains. The absorption and Faraday rotation spectra in the IR range and the transverse Kerr effect spectra in the visible spectral range for these samples are measured. The absorption and magneto-optical effect spectra are in agreement with the corresponding spectra of single crystals. The appearance of additional absorption bands at 2 and 3 μm is associated with the violation of the stoichiometry of the nanogarnet and the possible contamination of the initial material. The specific Faraday rotation in the transparency window is approximately 1.5 times smaller than the corresponding quantity for single crystals. The extrema in the Kerr effect spectra coincide with those for single crystals, are smaller in magnitude, and are smeared. On the whole, the prepared bulk samples are transparent in the IR spectral range and exhibit optical and magneto-optical characteristics comparable to the corresponding parameters for single crystals. The high density of point defects of the nanogarnet is primarily due to the violation of the stoichiometry and the valence state of iron ions.

Evolution of magnetooptical and transport properties of La1−xAgxMnO3 films depending on silver concentration

Evolution of optical, magnetooptical, and transport properties of La1−xAgxMnO3/SrTiO3 epitaxial films depending on the silver concentration (x = 0.05, 0.10, 0.15, and 0.25) is studied. The highest values of the Curie temperature (TC ≈ 317 K), magnetoresistance (∼16%), magnetotransmission (∼8%), and transverse Kerr effect (δ ∼ 20 × 10−3) are attained for a concentration x = 0.10 of Ag+ ions. Comparison of the temperature dependences of the transmission of IR radiation, resistivity, magnetotransmission, magnetoresistance, and Kerr effect indicates electronic and magnetic inhomogeneity of the films in spite of saturation of films with silver. This feature of the film state is explained using the concepts of epitaxial stresses and metastable point defects.