Papers by Keyword: Jahn-Teller Effect

Abstract: The magnetic field dependence of ultrasonic attenuation α (B) of slow shear waves in the ZnSe:Cr²⁺ crystal at a number of fixed temperatures from T=1.4 K to 20 K in magnetic fields of up to B=14 T were investigated. For magnetic fields B above 5 T we found that the attenuation increases with B monotonically, and at a given temperature it is proportional to the magnitude of relaxation attenuation at B=0. We show that the magnetic field dependent attenuation is due to the change in populations of the lowest energy levels of the impurity centers Cr_Zn4Se, produced by the Jahn-Teller effect and split by the spin-orbital interaction and the magnetic field. The calculations carried out without fitting parameters are in good agreement with the experimental data.

Abstract: Structure phase transitions in nonstoichiometry oxides with perovskite structure were considered. The microscopic description of cooperative Jahn-Teller transition was suggested and the effects caused by mechanical activation of oxide systems (their conversion into nanostructural state, acceleration of oxidation-renewal reactions and immiscibility) were analized. The correspondence of the theoretical results to the data of experiment on phase states of mechanically activated oxide NdMnO₃ is shown.

Abstract: Ultrasonic investigation of ZnSe:Cr²⁺ crystal was carried out at low temperatures in magnetic field applied along the wave vector. The observed anomalies in magnetic field dependences of attenuation and wave number evidence for existence of resonant transitions between the energy levels of the Jahn-Teller tetrahedral complex CrSe₄.

Abstract: The theoretical model of the crystal structure of lanthanum manganite doped by non-Jahn-Teller ions is proposed. In order to describe the changes in the crystal structure and orbital state of manganese ions subsystem, we use modified shell model and virtual crystal model. The orbital ordering collapse is explained in terms of dynamical Jahn-Teller effect. The model of superexchange interaction helps to find the values of antiferromagnetic and ferromagnetic exchange parameters for dynamical and static orbital states of interacting ions. The magnetic structure of LaMn_1-xGa_xO₃ is explained and magnetic resonance spectrum is predicted.

Abstract: The decrease of initial relative permeability at 103-106Hz is observed in MgCuZn or MnMgCuZn ferrites. By measuring the temperature dependence of loss factor, the gradual deterioration of initial relative permeability is attributed to a relaxation phenomenon. The relaxation phenomena of MnMgCuZn ferrites occur in the condition of the stoichiometoric composition and the higher sintering temperatures. The activation energies of the relaxation phenomena are calculated to be 0.3-1.0eV. The relaxation times at infinite temperature are calculated to be 10-12-10-16 second. The initial relative permeability of MgCuZn or MnMgCuZn ferrites with the relaxation phenomena is higher than the value calculated from the resonance frequency and Snoek’s limit law.