Quantum mechanical characteristic of magnetic charges in artificial magnetic honeycomb lattice

The intriguing physics of magnetic honeycomb lattice has drawn lot of attention in both the bulk and the two-dimensional nanostructured specimens. The artificially engineered honeycomb system manifests the two-dimensional projection of spin ice where magnetic charges are confined to the vertices due to magnetic Coulomb’s interaction. It provides unique opportunity to unravel both the classical and the quantum magnetic properties in reduced dimensionality. While the macroscopic spin of individual element renders the occurrence of entropy driven classical phenomenology, the Pauli matrix representation of magnetic charge quasi-particle enables the exploration of emergent quantum mechanical ground state properties. Quantum disordered state of magnetic charges is one such example. In addition to the inherent geometrical frustration, the competing nature of exchange interactions (J₁, J₂ terms) in thermally tunable artificial magnetic honeycomb lattice of single domain size elements provides a disorder-free environment to the exploration of quantum disorderness at low temperature. Our detailed neutron-centric research works have revealed massively degenerate dynamic ground state of magnetic charges in permalloy (Ni_0.81Fe_0.19) honeycomb that remain unperturbed to magnetic field application. The charges relax by emitting or absorbing a net magnetic charge defect or magnetic monopole between the vertices. In an important finding, for the first time we have not only quantitatively determined the magnetic charge relaxation rate, ~ 20 ps, in an artificial spin ice but have also demonstrated the intrinsic quantum mechanical nature of magnetic charge dynamics, thus establishing its quasi-particle characteristic. Besides the fundamental importance, the quasi-particle has direct implication to the spintronics research. We have discovered that charge relaxation propels electrical conduction via indirect interaction with electric carriers in the recently reported magnetic diode effect in permalloy honeycomb lattice. It elucidates a practical aspect of magnetic charge physics in the design of next generation spintronic devices.