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

Abstract

The magnetic and electronic properties of K 2 Fe 2 B 2 O 7 with a three dimensional network of isolated FeO 4 tetrahedra are systematically studied on the basis of first principles density functional calculations. Our results demonstrated that K 2 Fe 2 B 2 O 7 is semiconducting, and Fe 3+ ions favor high spin states. By evaluating its spin exchange interactions, we found that the dominated spin interaction in K 2 Fe 2 B 2 O 7 comes from Fe–O–Fe bridge, which is antiferromagnetic coupling. Morevoer, in the ab plane, the Fe 3+ 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. • Our analysis indicates that K 2 Fe 2 B 2 O 7 is semiconducting, and Fe 3+ ions favor high spin states. • The dominated spin interaction in K 2 Fe 2 B 2 O 7 comes from Fe–O–Fe bridge, which is antiferromagnetic coupling. • Fe 3+ 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.