Magnetic transitions in the chiral armchair-kagome system Mn2Sb2O7

Abstract

The competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. ${\mathrm{Mn}}_{2}{\mathrm{Sb}}_{2}{\mathrm{O}}_{7}\phantom{\rule{0.16em}{0ex}}\mathrm{forms}$ in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. ${\mathrm{Mn}}_{2}{\mathrm{Sb}}_{2}{\mathrm{O}}_{7}\phantom{\rule{0.16em}{0ex}}\mathrm{exhibits}$ two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the $P{3}_{1}21$ space group, ${\mathrm{Mn}}_{2}{\mathrm{Sb}}_{2}{\mathrm{O}}_{7}\phantom{\rule{0.16em}{0ex}}\mathrm{actually}$ crystallizes in $P2$, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional ``armchair-kagome'' lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems.