Magnetic and electronic properties of frustrated spin dimer compound K2Fe2B2O7: A first-principles calculation

• Our analysis indicates that K2Fe2B2O7 is semiconducting, and Fe3+ ions favor high spin states.
• The dominated spin interaction in K2Fe2B2O7 comes from Fe–O–Fe bridge, which is antiferromagnetic coupling.
• Fe3+ ions form an almost two dimensional triangle plaquettes and the three intra-layer spin exchange interactions are all antiferromagnetic, which results in the geometric frustration.

The magnetic and electronic properties of K2Fe2B2O7 with a three dimensional network of isolated FeO4 tetrahedra are systematically studied on the basis of first principles density functional calculations. Our results demonstrated that K2Fe2B2O7 is semiconducting, and Fe3+ ions favor high spin states. By evaluating its spin exchange interactions, we found that the dominated spin interaction in K2Fe2B2O7 comes from Fe–O–Fe bridge, which is antiferromagnetic coupling. Morevoer, in the ab plane, the Fe3+ ions form an almost two dimensional triangle plaquettes and the three intra-layer spin exchange interactions are all antiferromagnetic, which results in the geometric frustration due to the three spin directions in the triangle cannot compromise with each other. Consequently, the interaction of strong spin dimer and geometric frustration leads to the observed spin glass behavior.