Phase separation in manganites induced by orbital-ordering strains

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Chemistry

Background:

• Doped manganite perovskites (AMnO3) display diverse electronic properties arising from coupled charge, spin, and orbital interactions.
• The Jahn-Teller distortion of Mn(3+) ions significantly influences the orbital degrees of freedom in these materials.
• Previous work identified a transition from orbital disorder to order around a cation size variance (σ²) of approximately 0.005 Ų in insulating manganites.

Purpose of the Study:

• To investigate the electronic properties of AMnO3 perovskites with varying cation size variance (σ²).
• To explore the coexistence of orbitally ordered and disordered phases in doped manganites.
• To understand the role of microstructural lattice strains in phase segregation phenomena.

Main Methods:

• Magnetization measurements were performed on a series of eight AMnO3 perovskite samples.
• Electron Spin Resonance (ESR) spectra were utilized to study the electronic properties.
• Samples were characterized by varying the cation size variance (σ²) at the A-site, with a fixed distribution of 70% trivalent lanthanides and 30% divalent cations (Ca, Sr, or Ba).

Main Results:

• A coexistence of orbitally ordered and disordered phases was observed in samples with σ² ranging from 0.0016 to 0.0040 Ų.
• A temperature difference of 40 K was found between the Curie temperatures of the coexisting phases.
• Orbital ordering strains were found to be dominant at larger σ² (> 0.005 Ų), leading to the observation of only the ordered phase.

Conclusions:

• The observed intermediate temperature phase segregation is attributed to the competition between orbital ordering and microstructural lattice strains.
• Strain-driven phenomena play a crucial role in the phase behavior of doped manganites.
• Understanding these phase transitions is key to tailoring the electronic properties of manganite perovskites.