Abstract
Magnetically frustrated systems provide fertile ground for complex behaviour, including unconventional ground states with emergent symmetries, topological properties, and exotic excitations. A canonical example is the emergence of magnetic-charge-carrying quasiparticles in spin-ice compounds. Despite extensive work, a reliable experimental indicator of the density of these magnetic monopoles is yet to be found. Using measurements on single crystals of Ho2Ir2O7 combined with dipolar Monte Carlo simulations, we show that the isothermal magnetoresistance is highly sensitive to the monopole density. Moreover, we uncover an unexpected and strong coupling between the monopoles on the holmium sublattice and the antiferromagnetically ordered iridium ions. These results pave the way towards a quantitative experimental measure of monopole density and demonstrate the ability to control antiferromagnetic domain walls using a uniform external magnetic field, a key goal in the design of next-generation spintronic devices.
Highlights
Frustrated systems provide fertile ground for complex behaviour, including unconventional ground states with emergent symmetries, topological properties, and exotic excitations
First we report the results of magnetisation and resistance measurements on single crystals of Ho2Ir2O7 under an applied magnetic field oriented along the [100] direction
Our results show that the isothermal magnetoresistance of Ho2Ir2O7 is strongly linked to the concentration of magnetic monopoles, in a way that holds promise to develop a readily measurable and versatile experimental indicator of their density
Summary
Frustrated systems provide fertile ground for complex behaviour, including unconventional ground states with emergent symmetries, topological properties, and exotic excitations. The Ir moments are coupled antiferromagnetically and, with the exception of Pr2Ir2O7, spontaneously order at low temperatures such that they point alternately all into/all out of adjacent tetrahedra12 The effect of this transition on the Ho moments is observed as a slight bifurcation of the field-cooled and zero-fieldcooled magnetic susceptibilities, which is most clear on subtraction of the two datasets (Fig. 1a). The ordered Ir moments produce a local effective magnetic field (hloc) at the Ho sites aligned either parallel or antiparallel to the local 〈111〉 directions (see Fig. 1c) These fields, when combined with the spin-ice physics, lead to a fragmented Ho 3I1O/1I3O monopole crystal ground state at sufficiently low temperatures. The experimental study of this anisotropic behaviour requires measurements on single crystals, something which has only become possible very recently for the pyrochlore iridates
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