Calculation of multipolar exchange interactions in spin-orbital coupled systems

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Materials Science

Background:

• Accurate computation of exchange interactions is crucial for understanding magnetic phenomena in materials.
• Spin-orbit coupling significantly influences magnetic properties, especially in heavy elements.
• Existing methods may not fully capture multipolar contributions to exchange interactions.

Purpose of the Study:

• To develop a novel computational method for calculating multipolar exchange interactions in spin-orbit coupled systems.
• To apply this method to uranium dioxide and investigate its magnetic coupling behavior.
• To analyze the interplay between superexchange and spin-lattice interactions.

Main Methods:

• Multipolar tensor expansion of the density matrix within the local density approximation plus U (LDA+U) electronic structure method.
• Mean-field approximation combined with the pair-flip approximation technique for mapping exchange constants to total energy calculations.
• Calculation of spin-lattice interaction to complement superexchange analysis.

Main Results:

• The developed method successfully computes multipolar exchange interactions.
• Uranium dioxide displays antiferromagnetic superexchange for dipoles but ferromagnetic coupling for quadrupoles, contradicting prior studies.
• Spin-lattice interaction is found to be of comparable magnitude to superexchange.

Conclusions:

• The new computational approach provides deeper insights into complex magnetic interactions.
• The distinct dipole and quadrupole couplings in uranium dioxide highlight the importance of multipolar effects.
• A competition between superexchange and spin-lattice interactions governs the quadrupolar behavior in uranium dioxide.