Intrinsic antiferromagnetic/insulating phase at manganite surfaces and interfaces

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Bilayer systems involving La(2/3)Sr(1/3)MnO(3) (LSMO) thin films are crucial for magnetic tunneling junctions.
• Understanding interfacial effects is key to optimizing device performance.
• The 'dead layer' phenomenon in manganite-based devices is not fully understood.

Purpose of the Study:

• Investigate interfacial effects in LSMO bilayer systems with various capping layers.
• Determine the origin of the 'dead layer' observed in manganite-based magnetic tunneling junctions.
• Elucidate the role of interfacial phase separation and structural disruption.

Main Methods:

• Surface-sensitive synchrotron radiation techniques were employed for detailed analysis.
• Transport measurements were conducted to assess electrical properties.
• Comparative studies were performed on capped and uncapped LSMO samples.

Main Results:

• A capping-layer-dependent variation in the Mn oxidation state at the interface was observed.
• An intrinsic antiferromagnetic/insulating phase, approximately two unit cells thick, was detected at the LSMO interface.
• This interfacial phase exists irrespective of the capping material, suggesting an intrinsic phenomenon.

Conclusions:

• The detected interfacial phase likely originates from preferential occupancy of Mn 3d orbitals.
• Structural disruption and broken inversion symmetry at the LSMO interface promote this phase separation.
• This intrinsic interfacial phenomenon is responsible for the depressed magnetotransport properties and the 'dead layer' in manganite-based magnetic tunneling junctions.