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Point defects, ferromagnetism, and transport in calcium hexaboride
1Laboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland.
Physical Review Letters
|October 3, 2001
Summary
A neutral boron vacancy in calcium hexaboride (CaB6) creates a magnetic moment. This finding suggests that surfaces and defects significantly contribute to CaB6
Area of Science:
- Solid-state physics
- Materials science
- Computational materials science
Background:
- Calcium hexaboride (CaB6) exhibits ferromagnetism, a property not fully explained by existing models.
- Understanding the origin of magnetism in CaB6 is crucial for its potential applications.
Purpose of the Study:
- To investigate the origin of local magnetic moments in CaB6.
- To determine the role of point defects and surfaces in CaB6 ferromagnetism.
Main Methods:
- Supercell approach within generalized gradient approximation (GGA) of density functional theory (DFT).
- Calculation of formation energies and local magnetic moments for point defects in CaB6.
Main Results:
- Substitution of calcium (Ca) by lanthanum (La) does not induce a local magnetic moment.
- A neutral boron vacancy (B6 vacancy) in CaB6 results in a local magnetic moment of 2.4 Bohr magnetons.
- Broken B-B bonds on (100) cleavage planes are identified as a key structural feature.
Conclusions:
- Neutral B6 vacancies are a primary source of local magnetic moments in CaB6.
- Both internal and external surfaces of CaB6 contribute significantly to its observed magnetization.
- The findings provide a mechanism for ferromagnetic ordering in CaB6.