arXiv subjects

R. Y. Gu

Publications and source records attributed to R. Y. Gu.

7 recordsLinked to original sources

arXiv2005

Quantum Spin Effect and Short-Range Order above the Curie Temperature

Using quantum Heisenberg model calculations with Green's function technique generalized for arbitrary spins, we found that for a system of small spins the quantum spin effects significantly contribute to the magnetic short-range order and strongly affect physical properties of magnets. The spin dynamics investigation confirms that these quantum spin effects favor the persistence of propagating spin-wave excitations above the Curie temperature. Our investigation suggests a reconsideration of prevailing point of view on finite temperature magnetism to include quantum effects and the magnetic short-range order.

cond-mat.other↗

arXiv2005

Magnetic Phase Transition in FeRh

Density functional calculations are performed to investigate the phase transition in FeRh alloy. The effective exchange coupling, the critical temperature of magnetic phase transition and the adiabatic spin wave spectrum have been obtained. Different contributions to the free energy of different phases are estimated. It has been found that the antiferro-ferromagnetic transition in FeRh occurs mostly due to the spin wave excitations.

cond-mat.other↗

arXiv2004

Joint effect of lattice interaction and potential fluctuation in colossal magnetoresistive manganites

Taking into account both the Jahn-Teller lattice distortion and the on-site electronic potential fluctuations in the orbital-degenerated double-exchange model, in which both the core-spin and the lattice distortion are treated classically, we investigate theoretically the metal-insulator transition (MIT) in manganites by considering the electronic localization effect. An inverse matrix method is developed for calculation in which we use the inverse of the transfer matrix to obtain the localization length. We find that within reasonable range of parameters, both the lattice effect and the potential fluctuation are responsible to the occurrence of the MIT. The role of the orbital configuration is also discussed.

cond-mat.str-el↗

arXiv2002

Essential Role of the Cooperative Lattice Distortion in the Charge, Orbital and Spin Ordering in doped Manganites

The role of lattice distortion in the charge, orbital and spin ordering in half doped manganites has been investigated. For fixed magnetic ordering, we show that the cooperative lattice distortion stabilize the experimentally observed ordering even when the strong on-site electronic correlation is taken into account. Furthermore, without invoking the magnetic interactions, the cooperative lattice distortion alone may lead to the correct charge and orbital ordering including the charge stacking effect, and the magnetic ordering can be the consequence of such a charge and orbital ordering. We propose that the cooperative nature of the lattice distortion is essential to understand the complicated charge, orbital and spin ordering observed in doped manganites.

cond-mat.str-el↗

arXiv2001

Novel Quantum Spin Assisted Tunneling in Half Metallic Manganite Tunnel Junctions

The electron tunneling in half metallic manganite tunnel junctions is studied by using a quantum mechanically treated double exchange model. We show that the stimulation of spin excitations, caused by the strong Hund's coupling between the conduction $e_g$ electrons and the localized quantum spins of the manganite ions, would assist electrons to tunnel through the junction even with the antiparallel aligned magnetizations of the electrodes. This mechanism gives rise to an extra tunnel conductance, in addition to that predicted by Julliere's model. Our theory is in good agreement with the voltage dependence of the tunnel conductance in manganite tunnel junctions observed by experiments.

cond-mat↗

arXiv1999

Linear spin and orbital wave theory for undoped manganites

We present a linear spin and orbital wave theory to account for the spin and orbital orderings observed experimentally in undoped manganite. It is found that the anisotropy of the magnetic structure is closely related to the orbital ordering, and the Jahn-Teller effect stabilizes the orbital ordering. The phase diagram and the low energy excitation spectra for both spin and orbital orderings are obtained. The calculated critical temperatures can be quantitatively comparable to the experimental data.

cond-mat.str-el↗

arXiv1999

Phase diagram of an extended Kondo lattice model for manganites: the Schwinger-boson mean-field approach

We investigate the phase diagram of an extended Kondo lattice model for doped manganese oxides in the presence of strong but finite Hund's coupling and on-site Coulomb interaction. By means of the Schwinger-boson mean-field approach, it is found that, besides magnetic ordering, there will be non-uniform charge distributions, such as charge ordering and phase separation, if the interaction between electrons prevails over the hybridization. Which of the charge ordering and phase separation appears is determined by a competition between effective repulsive and attractive interactions due to virtual processes of electron hopping. Calculated results show that strong electron correlations caused by the on-site Coulomb interaction as well as the finite Hund's coupling play an important role in the magnetic ordering and charge distribution at low temperatures.

cond-mat.str-el↗