Ordered states of Jahn-Teller distorted MnO6 octahedra in weakly doped lanthanum-strontium manganites

Physics of the Solid State - This paper presents the results of investigations of the ordering of Jahn-Teller distorted MnO6 octahedra in lightly doped single crystals of the composition La1...     

Anti-phase domain structuring in oxide ferroelectrics: Physical properties and application

The results from studies of domain borders by the optical and acoustic topography methods in LiNbO₃:Fe samples are presented. The formation of Fe ion concentration gradients, a change in the refractive index, and a gradient of the photoinduced field and parameters of acoustic waves near the domain borders were observed. It is shown that main reason for the distortion of crystalline structure parameters is the formation of photoinductive field gradients of spatially separated Fe₂₊ and Fe₃₊ ions.     

Acoustic and magnetic properties of La<Subscript>0.825</Subscript>Sr<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript> lanthanum manganites

This paper reports on measurements of the acoustic, magnetic, and electrical properties and on an x-ray microprobe analysis of a La_0.825Sr_0.175MnO₃ single-crystal sample. The acoustic studies were made with a pulsed acoustic spectrometer operating on a 770-MHz carrier. The studies revealed anomalies in the damping coefficients and sound velocity near 300, 200 K, and the Curie temperature T_C (283 K) where the colossal magnetoresistance occurs. The effect of a magnetic field on the magnetic texture of lanthanum manganites cooled below T_C, observed earlier in samples of other composition, is confirmed. In addition, a region was found wherein the magnetic susceptibility of an unclamped sample behaves anomalously. The electrical resistivity was observed to decrease substantially below T_C; this effect exhibits a hysteretic pattern in the interval 200–180 K.     

Propagation of high-frequency acoustic waves through the structure of Jahn-Teller ions in lithium niobate with iron

This paper reports on the results of an investigation into the specific features of the propagation of acoustic waves in lithium niobate LiNbO₃ with iron ions under laser irradiation of regions with increased and decreased concentrations of Fe²⁺ ions. It is shown that the observed effects of local variations in the damping and velocity of acoustic waves are associated with the strong electron-phonon interaction of Jahn-Teller Fe²⁺ ions.     

Highly heterogeneous distributions of gadolinium impurities in Pb1 − x Gd x Te crystals when x > 0.005

Two types of Gd³⁺ impurity centers are identified in heavily doped narrow-gap PbTe semiconductor by means of EPR at a frequency of 9.3 GHz and temperature T = 4.2 K. Magnetic properties of both centers have cubic symmetry, but their EPR spectra are characterized with different fine structure constants. The origin of the centers and their characteristics are discussed.     

Magnetic birefringence of light in hematite

Peculiarities in the propagation of IR radiation in the easy-plane antiferromagnet α-Fe₂O₃ are investigated. In the geometry of the Cotton-Mouton effect, magnetic birefringence is measured and magnetooptical constants are estimated.     

Photoinduced decrease in local polarization switching fields in lithium niobate crystals

Variations in local polarization switching fields E _C in lithium niobate crystals have been investigated under laser irradiation of the z surface. It has been established that the simultaneous application of an electric field in the direction opposite to the spontaneous polarization field and laser beam leads to a decrease in the field E _C .     

Role of nanosecond processes in the formation of domains in ferroelectric crystals

The contribution from pyroelectric and photovoltaic effects to the formation of light-induced domains in crystals of oxide ferroelectrics of lithium niobate type upon irradiation by nanosecond focused laser beams is considered. It is established that inverted domains are formed in irradiated regions under the combined effect of generated pyroelectric and photovoltaic fields with a sharp increase in temperature. It is shown that the most stable domains are formed in lithium niobate samples containing Fe²⁺ and Fe³⁺ impurity ions.     

Photon-phonon interaction on periodic structures

Features of the interaction between optical and acoustical waves with the same wavelength and multiple of the structural layer period, propagating simultaneously through periodic structures, are analyzed. The current state of and prospects for photon-phonon crystals being used for amplification, the generation of gigahertz acoustic waves, and other nonlinear optical and acoustic effects are examined.     

Magnetoinduced structural,Jahn–Teller,dielectric, and transport effects in La<Subscript>0.875</Subscript>Sr<Subscript>0.125</Subscript>MnO<Subscript>3</Subscript>

The temperature and magnetic field dependences of elastic moduli and resistance are studied in a La_0.875Sr_0.125MnO₃ single crystal. In addition to the metal–insulator transition, the structural transition from the cooperative J–T strongly distorted orthorhombic phase to the charge ordering phase is studied at T _J–T = 150 K in magnetic fields of up to 2 T. Results show it is possible to control the acoustic parameters in the vicinity of T _J–T via magnetic fields.