Phase transition in perovskite manganites with orbital degree of freedom

Abstract

Roles of orbital degree of freedom of Mn ions in phase transition as a function of temperature and hole concentration in perovskite manganites are studied. It is shown that the orbital order-disorder transition is of the first order in the wide region of hole concentration and the Néel temperature for the anisotropic spin ordering, such as the layer-type antiferromagnetic one, is lower than the orbital ordering temperature due to the anisotropy in the orbital space. The calculated results of the temperature dependence of the spin and orbital order parameters explain a variety of the experiments observed in manganites.

Orbital ordering inLaMnO3:Electron-electron and electron-lattice interactions

“…The orbital ordered state is determined in the mean field approximation. 33 By applying the Holstein-Primakoff transformation to the spin operators, the dispersion relation of the spin wave is calculated. Experimentally, the spin wave in LaMnO 3 was measured by the neutron scattering experiments in Refs.…”

Theory of Raman scattering from orbital excitations in manganese oxides

“…We investigate the orbital states at the paramagnetic and A-AF phases by applying the mean field approximation. 25 A unit cell which includes four Mn sites is adopted. These Mn sites are termed A 1 , A 2 , B 1 and B 2 (see Fig.…”

Magnetic Glassiness below Curie Temperature in La0.8Ca0.2MnO3

“…4) Recent studies revealed that the DE scenario alone cannot explain the whole physics occurring in the manganite system and thereby the interplay among spin, charge, orbital, and lattice should be invoked to render more precise explanations on the CMR phnomenon. [5][6][7] It has been suggested that the magnetic polaron attributable to combined effect of lattice distortions and magnetic clusters is a probable origin of CMR effect, designating that short-range interactions is a crucial factor to be taken. 8) Recently, Dai et al investigated on the low-doped system La 1Àx Ca x MnO 3 (0:15 x 0:3) by means of neutron diffuse scattering technique, revealing that the short-range charge (polaron) couplings persist even in the low temperature regime and affect the electrical transport properties.…”