Anomalous Hall Effect of Pyrochlore Mo Oxides with Spin Charlity
Yoshinori Tokuraa
Spin Superstructure Porject, ERATO, JST, c/o AIST, Tsukuba 305-0046, Japan
aDepartment of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
An electron hopping on non-colanar spin sites with spin chirality obtains a Berry phase that acts as an internal fictious magnetic field. The unconventioanl anomalous Hall effects observed in pyrocholre-type Nd2Mo2O7 and related compounds are shown to arise from this effect.
Charge ordering, phase separation and electron transport in manganites
Maxim Yu. Kagana, Kliment I. Kugelb, Alexander L. Rakhmanovb
aP.L.Kapitza Institute for Physical Problems, Kosygin street 2, 117334 Moscow, Russia
bInstitute for Theoretical and Applied Electrodynamics, Izhorskaya street 13/19, Moscow, Russia
A simple model of CO is considered. It takes into account both the Coulomb repulsion at neighboring sites and the essential magnetic interactions. It is shown explicitly that at any deviation from half-filling (n ¹ 1/2) the system is unstable with respect to phase separation into the regions corresponding to CO n = 1/2 and metallic regions with smaller electron or hole density. Possible structure of this phase-separated state (metallic droplets in the CO matrix) is discussed. We estimate the parameters of these droplets and construct the phase diagram. We calculate the conductivity, magnetoresistance and noise spectrum for the phase-separated state. The charge transfer in the system is assumed to occur due to the electron tunneling from one droplet to another.
Anisotropy of energy transport and spin-phonon interaction in S=1/2 chain cuprate BaCu2Si2O7
A. V. Sologubenkoa, H. R. Otta, G. Dhalenneb, A. Revcolevschib
aLaboratorium für Festkörperphysik, ETH Hönggerberg, CH-8093 Zürich, Switzerland
bLaboratoire de Physico-Chimie des Solides, Université Paris-Sud, 91405 Orsay, France
The thermal conductivity k of the spin-1/2 chain cuprate BaCu2Si2O7 was measured along different crystallographic directions in the temperature region between 0.5 and 300 K. The thermal conductivity along the chain direction considerably exceeds that along perpendicular directions. Near the antiferromagnetic transition at TN = 9.2 K the data indicates enhanced scattering of phonons by critical fluctuations in the spin system. Applying external magnetic fields as large as 6 T has little influence on the behaviour of k(T). The spin contribution to the energy transport is estimated from the anisotropy of k(T) and from the strength of the scattering of phonons near TN.
Peculiar Roles of Spins in the Thermal Conductivity of Pure and Doped La2CuO4: Comparison with CuGeO3
Yoichi Ando, X. F. Sun, J. Takeya, Seiki Komiya
Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
In magnetic materials, spin excitations can carry heat and scatter electrons and phonons, thereby affecting the thermal conductivity. Recent studies of the heat transport in low-dimensional cuprate systems [e.g. Y. Ando et al., PRB 58 (1998) R2913] have demonstrated that the spin-related heat transport is very useful for extracting information on the peculiar spin systems in these compounds. In this talk, we report measurements of the anisotropic thermal conductivity k of pure, hole-doped, and Zn-doped La2CuO4 single crystals, and discuss the roles of magnons and the spin stripes in the heat transport in these systems. Comparison with the heat transport in CuGeO3, which shows similar k(T) behavior as that of La2CuO4, gives us a lesson of how the behavior of k(T) reflects the difference in the spin ground states.
Magnetization rotation or generation of incoherent spin waves? Suggestions for a spin-transfer effect experiment.
Ya.B. Bazaliya, B.A. Jonesb
aArgonne National Laboratory, MSD, 9700 S. Cass Ave, Argonne, IL 60439, USA
bIBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.
``Spin-transfer'' torque is created when electric current is passed through metallic ferromagnets and may have interesting applications in spintronics. So far it was experimentally studied in ``collinear'' geometries, where it is difficult to predict whether magnetization will coherently rotate or spin-waves will be generated. Here we propose an easy modification of existing experiment in which the spin-polarization of incoming current will no longer be collinear with magnetization and recalculate the switching behavior of the device. We expect that a better agreement with the magnetization rotation theory will be achieved. That can be an important step in reconciling alternative points of view on the effect of spin-transfer torque.