Insulating ferromagnetism in La4Ba2Cu2O10: an Ab initio wannier function analysis.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Half-filled layered cuprates present complex magnetic behaviors, notably insulating ferromagnetism in La4Ba2Cu2O10.
• Understanding the microscopic origins of magnetism in these materials is crucial for developing novel electronic devices.

Purpose of the Study:

• To elucidate the microscopic mechanisms behind the insulating ferromagnetism in La4Ba2Cu2O10.
• To investigate the magnetic ordering in isostructural Nd4Ba2Cu2O10 and compare it with La4Ba2Cu2O10.
• To explore the influence of pressure on the magnetic properties of these materials.

Main Methods:

• Utilized energy-resolved Wannier states to analyze microscopic magnetic interactions.
• Evaluated key parameters including hopping (t), on-site Coulomb repulsion (U), and exchange coupling (J).
• Investigated magnetic coupling beyond nearest neighbors and the role of dimensionality.

Main Results:

• Identified intersite direct exchange as the dominant ferromagnetic coupling mechanism in La4Ba2Cu2O10, overpowering antiferromagnetic superexchange.
• Revealed that Nd4Ba2Cu2O10 exhibits antiferromagnetic order due to its 1D chain characteristics.
• Found that in-plane magnetic order in both compounds is not governed by nearest-neighbor interactions.
• Predicted a pressure-induced transition from ferromagnetic to antiferromagnetic ordering.

Conclusions:

• The study highlights the significance of direct exchange in certain cuprates, challenging existing paradigms.
• The distinct magnetic behaviors of La4Ba2Cu2O10 and Nd4Ba2Cu2O10 underscore the role of dimensionality and specific interactions.
• The predicted pressure-induced transition opens avenues for external control of magnetic states in these materials.