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Magnetism and phase transitions in LaCoO3
A M Durand1, D P Belanger, C H Booth
1Department of Physics, University of California, Santa Cruz, CA 95064, USA.
Summary
Lattice strain induces weak ferromagnetism in LaCoO3 (LCO) by affecting the Co-O-Co angle, particularly near surfaces and interfaces. This magnetic ordering is influenced by structural changes and temperature-dependent magnetic interactions.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Magnetism
Background:
- LaCoO3 (LCO) exhibits complex magnetic phase transitions influenced by external factors.
- Understanding these transitions is crucial for developing advanced magnetic materials.
Purpose of the Study:
- To investigate the phase transitions in LaCoO3 (LCO) under varying magnetic fields (H).
- To elucidate the role of lattice strain and the Co-O-Co angle in inducing ferromagnetic (FM) order.
Main Methods:
- Neutron scattering and magnetometry measurements were employed.
- Curie-Weiss analysis was used to study magnetic interactions.
- Structural parameters and their dependence on temperature and Co-O-Co angle were analyzed.
Main Results:
- A ferromagnetic (FM) transition was observed at approximately 87 K for low magnetic fields (H ≤ 100 Oe).
- Predominantly antiferromagnetic (AFM) interactions were found for T > Tc, with magnetic frustration indicated by the lack of long-range AFM order.
- Weak ferromagnetism in bulk LCO is attributed to lattice strain at surfaces and interfaces, influencing the Co-O-Co angle (γ).
- A critical Co-O-Co angle (γC) of 162.8° was determined for ferromagnetic long-range order.
- Below a critical temperature (To ≈ 37 K), FM order is confined to surface regions due to lattice strain.
Conclusions:
- Lattice strain is a key factor in inducing weak ferromagnetism in LaCoO3, particularly in thin films, nanoparticles, and near bulk surfaces/interfaces.
- The Co-O-Co angle plays a critical role in determining the magnetic ordering, with FM order favored above a specific critical angle.
- Magnetic frustration exists due to competing AFM interactions and the absence of long-range AFM order.
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