A. R. Bulatov

Acoustic and magnetic properties of La0.825Sr0.175MnO3 lanthanum manganites

This paper reports on measurements of the acoustic, magnetic, and electrical properties and on an x-ray microprobe analysis of a La0.825Sr0.175MnO3 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 TC (283 K) where the colossal magnetoresistance occurs. The effect of a magnetic field on the magnetic texture of lanthanum manganites cooled below TC, 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 TC; this effect exhibits a hysteretic pattern in the interval 200–180 K.

Features of high-frequency ultrasound propagation in the temperature range of structural and magnetic phase transitions in La1−xSrxMnO3 (x=0.175) manganite

The propagation of ultrasonic waves at a frequency of 770 MHz in a La0.825Sr0.175MnO3 single crystal is investigated in the temperature range 350–150 K. It is found that the velocity, attenuation, and mode composition of ultrasonic waves change at temperatures of 315–280 and 220 K. These changes correlate with the structural and magnetic phase transitions and can be explained in terms of the Jahn-Teller distortions of the crystal lattice.

Lattice, electrical, and magnetic effects in lanthanum manganites La1−xSrxMnO3 (x = 0.125, 0.150, 0.175)

The temperature dependences of the velocities of transverse and longitudinal hypersound in lanthanum strontium manganites of the composition La1−xSrxMnO3 (x = 0.125, 0.150, 0.175) have been measured at frequencies of 0.5–0.7 GHz. The structural phase transitions have been revealed, and their positions have been confirmed by data on the electrical resistance and magnetic measurements performed using the same samples. The results obtained have been analyzed in the framework of the model of competing Jahn-Teller distortions and magnetic ordering. The anomalies observed in the behavior of the velocities of longitudinal hypersound have been attributed to the local Jahn-Teller distortions, and their suppression due to the magnetic ordering has been considered a possible factor responsible for the colossal magnetoresistance.

Acoustic anomalies near phase transitions in manganite

The behavior of the velocities and attenuation of ultrasonic waves propagating in La1−xSrxMnO3 (x=0.175) manganite at frequencies of 700–800 MHz is studied in the temperature interval from 320 to 180 K, and the effect of magnetic field on the acoustic parameters is investigated. The transformation of acoustic modes in the vicinity of the magnetic phase transition is observed. The changes in the acoustic parameters near the structural and magnetic phase transitions are shown to be related to the strong spin-phonon and electron-phonon interactions.

Transformation of the acoustic mode near the structural and magnetic phase transitions in La1–xSrxMnO3 (x = 0.175) crystal

The peculiarities of the phase transitions in La0.825Sr0.175MnO3 single crystal have been investigated by acoustic methods at the frequency f = 770 MHz. Generation of a magnetoelastic wave near the phase transition at 305 K is revealed, which is assigned to quasi-transverse modes. The most likely cause of the phase transition near T = 305 K and the formation of the quasi-transverse mode is the suppression of local Jahn-Teller distortions.

Effect of Jahn-Teller distortions on the structural and magnetic ordering in perovskite-type transition-metal oxides

The effect of local and cooperative distortions of oxygen octahedra containing Jahn-Teller ions on the elastic, electric, magnetic, and optical properties of lightly doped lanthanum strontium manganites and irondoped lithium niobate ferroelectric has been experimentally investigated. The formation of nano-and microscale clusters and domains around, respectively, Mn3+ and Fe2+ Jahn-Teller ions at phase transitions and in magnetic or electric fields were studied. A model is proposed to consistently explain the results of the investigations of Jahn-Teller ions in magnetic and/or electrically ordered materials.

High-frequency ultrasonic studies of the structural phase transition in an La0.875Sr0.125MnO3 single crystal

The specific features of a phase transition from a disordered orbital state to an ordered orbital state in an La0.875Sr0.125MnO3 single crystal are investigated using acoustic methods at a frequency f = 500 MHz. The phase transition is accompanied by a distortion of MnO6 octahedra due to the cooperative Jahn-Teller effect and is a first-order phase transition, as judged from the sharp change observed in the damping of acoustic pulses, the acoustic wave velocity, and the temperature hysteresis. It is revealed that the parameters of the acoustic waves change significantly throughout the temperature range of existence of the cooperatively distorted structure. In an external magnetic field, the structural phase transition is shifted toward lower temperatures.

Influence of the Jahn-Teller effect on the structural, magnetic, and electrical properties of lightly doped manganites

Features of the structural, magnetic and electric properties in lightly doped La1−xSrxMnO3 (0.12 < x < 0.18) manganites are studied. Agreement between the types of orbital ordering and the local cooperative Jahn-Teller distortion octahedra is established. The interaction between the Jahn-Teller effect and magnetic ordering is described.

Formation of submicron partially ordered domain structures in ferroelectric and magnetic materials

Formation of domains and partially ordered periodic domain structures in ferroelectric and magnetic oxides of metals of transition groups has been investigated. Physical features of appearance of submicron periodic domain structures and possibilities of their use for the control over the parameters of high-frequency acoustic waves have been considered using the example of single crystals of lithium niobate and lanthanum-strontium manganites.

Ferroelectric and magnetic media with nanoscale regular domain structures

The formation and physical characteristics of irregular nano- and microscale domain structures were studied in ferroelectric and magnetic perovskite metal oxides. Their nonlinear optical, magnetic and elastic characteristics were established. The prospects for their application in the frequency and mode transformation of optical and acoustic waves are examined.