Spin-orbital order in the undoped manganite LaMnO3 at finite temperature

Abstract

We investigate the evolution of spin and orbital order in undoped LaMnO3 under increasing temperature with a model including both superexchange and Jahn-Teller interactions. We used several cluster mean field calculation schemes and find coexisting A-type antiferromagnetic (A-AF) and C-type alternating orbital order at low temperature. The value of the Jahn-Teller coupling between strongly correlated eg orbitals is estimated from the orbital transition temperature at TOO 780 K. By a careful analysis of on-site and on-bond correlations we demonstrate that spinorbital entanglement is rather weak. We have verified that the magnetic transition temperature is influenced by entangled spin-orbital operators as well as by entangled orbital operators on the bonds but the errors introduced by decoupling such operators partly compensate each other. Altogether, these results justify why the commonly used disentangled spin-orbital model is so successful in describing the magnetic properties and the temperature dependence of the optical spectral weights for LaMnO3. Published in: Physical Review B 94, 214426 (2016).

Spin-orbital model of stoichiometric LaMnO3 with tetragonal distortions

“…Hund's exchange stabilizes large spins S = 2 in LaMnO 3 and quantum effects are then reduced. Thus spin-orbital entanglement is small as we have shown in a recent study [16]. Then an additional advantage is that the analysis is simpler here than for some systems with smaller spins (such as S = 1/2 in KCuF 3 ) where spin-orbital entanglement cannot be neglected [17,18].…”

“…In the previous works the LaMnO 3 crystal electronic structure was investigated with the aid of pure electronic superexchange Kugel-Khomskii-like models [14][15][16]. Typically, such models are formulated in terms of the ionic spin-orbital degrees of freedom for Mn ions (all other degrees of freedom are integrated out, including degrees of freedom attributed to the bridge atoms).…”

“…In our previous work [16] we concentrated on the influence of the diverse entanglements (spin-orbital on-site and on-bond entanglement) on the electronic state of the LaMnO 3 crystal. The goal of the present work is to assess the influence of the crystal tetragonal deformation and to identify the main underlying physical mechanisms playing a role for a realistic description.…”

Генерация Свч-Колебаний В Сверхпроводниковой Туннельной Меза-Структуре С Прослойкой Из Ферромагнитного Изолятора

“…Согласно модели [19], в эксперименте наблюдается рост частоты генерации с увеличением тока через меза-структуру. Необходимое для образования спиновых завих-рений сильное спин-орбитальное взаимодействие [20], относительно слабое в автономном манганите LMO [21], может быть усилено за счет ян-теллеровского искажения в меза-структуре из-за влияния нижней пленки YBCO [22], а также наличием прослойки из золота, спин-орби-тальное взаимодействие в котором анализировалось в работе [23].…”

Superconducting mesa-structures with a spin filtering manganite interlayer

“…Another coincidence of the results of the experiment and the model [19] is the increase of generation frequency with increasing of bias current through the mesa-structure. The strong spin-orbit interaction, which is relatively weak in the autonomous manganite LMO [21], and which is necessary for the formation of spin vortices, can be enhanced due to JahnTeller distortion in the mesa-structure due to the influence of the lower YBCO film grown on the NGO substrate [22], and also by the presence of an interlayer of gold, the spin-orbit interaction in which was analyzed in [23]. In conclusion, the YBCO/LMO/Au-Nb mesa-structure with the spin-filter properties demonstrated microwave generation in GHz frequency band with a linewidth of order 50 MHz under the influence of external weak magnetic field |H| <10 Oe and the bias current.…”