V.I. Ozhogin

Nonlinear dynamics of coupled systems near magnetic phase transitions of the “order-order” type

Abstract The results are reviewed of the 15-year development of the concept of effective anharmonicity of the normal modes that describe the vibrations of a continuous medium having two or more mutually coupled subsystems. Magnetoelastic interaction near a spin reorientation phase transition leads to a giant acoustic nonlinearity and its magnetic field sensitivity in antiferromagnets such as α-Fe 2 O 3 , FeBO 3 , TmFeO 3 , etc.

Oxygen isotope effect in LaSrCuO system with Tc modified by Ni and Zn doping

Abstract The effect of the oxygen isotope substitution on the superconducting transition temperature T c has been studied in La 1.85 Sr 0.15 Cu 1−x Ni x O 4 (x=0; 0.005; 0.01; 0.015; 0.02; 0.025; 0.03), La 1.85 Sr 0.15 Cu 1−x Zn x O 4 (x = 0.0; 0.1) and La 2−x Ca x CuO 4 (x = 0.1; 0.08) oxides. The isotope shift exponent α increases with the T c fall down. The results are in a good agreement with the BSC based theory of magnetic pair breaking.

Interlayer CuO2 antiferromagnetic spin correlations in Tl-based superconducting Tl2Ba2CanCun+1O6+2n and Tl0.5Pb0.5Sr2Ca0.8Y0.2Cu2O7 oxides: 63Cu and 205Tl NMR and spin-lattice relaxation data

Abstract We analyzed 205 Tl and 63 Cu spin-lattice relaxation rate data T −1 1 for thallium-based Tl 0.5 Pb 0.5 Sr 2 Ca 0.80 Y 0.2 Cu 2 O 7 ( T ons c = 107 K) and Tl 2 Ba 2 Ca n Cu n +1 O 6+1 n ( T ons c = 104 K) ( n = 1), T ons c = 125 K ( n = 2)) cuprates which contain one or two TlO layers, respectively. The difference in temperature dependences T −1 1 ( 63 Cu) and T −1 1 ( 205 Tl) for the one TlO layer compound gives us evidence for the presence of interlayer antiferromagnetic spin correlations between the nearest copper atoms placed in the neighbouring CuO 2 layers.

Anomalous isotope effect in high-temperature superconductor LSCO with 3d-impurities

Abstract The influence of transition metal substitutions (Ni, Fe, Co) and Zn at the Cu sites on T c and the oxygen isotope effect α o has been studied in the system La 2− y Sr y Cu 1− x M x O 4 with the optimum ( y = 0.15) and overdoped ( y = 0.20) compositions. Essential distinctions in the behavior of parameter α o for systems with heterovalent Fe and Co substitutions and isovalent Ni and Zn substitutions have been revealed. For Fe doped compounds with y = 0.15 the isotope effect was found to be very large: α o ≈ 1.3 at x = 0.011. The dependence of the isotope effect on the substituted atom concentration changes substantially when the degree of strontium doping varies. The experimental data were theoretically analyzed on the basis of the phonon mechanism of superconductivity and the concept of the existence of a singularity in the electron density of state N ( E F ). It is shown that the influence of paramagnetic impurities on the T c isotope shift of superconductors is enhanced when there is a sharp peak in N ( E F ). The difference in these effects for a system with the optimum strontium composition and for an overdoped system is also explained.

Isotopic disorder in Ge single crystals probed with73GeNMR

NMR spectra of 7 3 Ge (nuclear spin I=9/2) in germanium single crystals with different isotopic compositions have been measured at the frequency of 17.4 MHz at room temperature. Due to the small concentration (∼0.1%) of the magnetic ( 7 3 Ge) isotope, the magnetic dipole-dipole interaction is negligible in the samples studied, and the observed specific features of the resonance line shapes (a narrow central peak and a wide plateau) are determined mainly by the quadrupole interaction of magnetic nuclei with the random electric-field gradient (EFG) induced by the isotopic disorder. The second and fourth moments of the distribution function of the EFG are calculated taking into account local lattice deformations due to mass defects in the close neighborhood of the magnetic nuclei, as well as charge-density redistributions and lattice strains induced by distant impurity isotopes. The simulated line shapes, represented by a superposition of Gaussians corresponding to individual transitions between nuclear Zeeman sublevels, agree reasonably well with the measured spectra.

73Ge NMR spectra in germanium single crystals with different isotopic composition

We have studied the influence of isotopic disorder on the local deformations in Ge single crystals from both experimental and calculation points of view. The nuclear magnetic resonance (NMR) spectra of73Ge nuclei (the nuclear spin equals 9/2) in perfect single crystals of germanium with different isotopic content were measured at temperatures 80, 300 and 450 K. Abnormal broadening of the spectrum was found to occur when the magnetic field was aligned along the [111] axis of a crystal. The observed specific angular dependence of the quadrupole broadening was attributed to isotopic disorder among atoms of germanium sited around the73Ge NMR probe. Local lattice deformations in germanium crystal lattice due to isotopic impurity atoms were calculated in the framework of the adiabatic bond charge model. The results obtained were applied to study random noncubic crystal field interactions with the nuclear quadrupole moments and corresponding effects in NMR spectra. Simulated second and fourth moments of resonance frequency distributions caused by the magnetic dipole-dipole and electric quadrupole interactions are used to analyze the lineshapes, theoretical predictions agree qualitatively with the experimental data.

On magnetoelastic soliton in antiferromagnet

Abstract The possibility of magnetoelastic solitary waves (solitons) propagation is considered for an easy plane antiferromagnet at various directions of the wave propagation velocity. The parameters of these solitons in AF are more favorable for the direct ac experiment than in elastic lattice or in ferromagnet.

XPS studies of Cu3+ ions in Ba(CuO2)2nH2O

X-ray photoelectron studies (XPS) were carried out for Cu3+ ions in Ba(CuO2)2nH2O. No intense satellites were observed in the spectra of Cu2p- electrons. The Cu2p32-level chemical shift was 1.4 and 2.4 eV when moving from Ba(CuO2)2nH2O (Cu3+) to CuO (Cu2+) and Cu2O (Cu1+), respectively.

The possibility of the giant isotope effect for ultrasound absorption in crystals

The effect of isotopic disorder on ultrasound absorption in germanium, silicon, and diamond crystals is considered. The “giant” isotope effect is predicted in the ultrasound absorption coefficient (in contrast to the isotope effect in the thermal conductivity and thermopower) of these crystals. The parameters determining the ultrasound absorption coefficients for the crystals under study with different degrees of isotopic disorder are determined from the known values of elastic moduli of the second and third order. The ultrasound absorption coefficients are analyzed as functions of temperature and wavevector for isotopically modified crystals. The possibility of experimental observation of this effect is considered.

Magneto-optical visualization of a sound-induced domain structure in hematite

Abstract Non-uniform spin states (stripe domains) are induced by powerful pulse ultrasonic waves in a hematite (α-Fe 2 O 3 ) single crystal. These states are visualized with the help of the Cotton-Mouton effect and quantitatively described in terms of an effective field proportional to the square of ultrasound amplitude.