Phase Transition in Perovskite Manganites with Orbital Degree of Freedom

TL;DR

This paper investigates how the orbital degree of freedom influences phase transitions in perovskite manganites, revealing first-order orbital order-disorder transitions and explaining experimental observations through theoretical calculations.

Contribution

It provides a theoretical analysis of the orbital and spin order transitions in manganites, highlighting the first-order nature of orbital transitions and the relationship between orbital and magnetic ordering temperatures.

Findings

Orbital order-disorder transition is first order over a wide hole concentration range.

Néel temperature for anisotropic spin order is lower than orbital ordering temperature.

Calculated temperature dependence of order parameters aligns with experimental data.

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 N$\rm \acute{e}$el 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.