Abstract
We theoretically investigate a classical Heisenberg model on the breathing pyrochlore lattice, where the nearest-neighbor (NN) exchange interactions for small and large tetrahedra, and , take different values due to the breathing bond alternation and is the third NN antiferromagnetic interaction along the bond direction. It is found by means of Monte Carlo simulations that for large , a hedgehog lattice, a three-dimensional periodic array of magnetic monopoles and antimonopoles, emerges in the form of a quadruple- state characterized by the ordering vector of , being irrespective of the signs of and/or as long as . It is also found that in an applied magnetic field, there appear six quadruple- states depending on the values of and , among which three phases including the in-field hedgehog-lattice state exhibit nonzero total chirality associated with the anomalous Hall effect of chirality origin. In the remaining two chiral phases, which are realized in the presence of ferromagnetic and/or , the spin structure is not topologically nontrivial, in spite of the fact that . The role of the topological objects of the monopoles in is also discussed.
13 More- Received 2 June 2022
- Accepted 1 August 2022
DOI:https://doi.org/10.1103/PhysRevB.106.064412
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