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arXiv · 2105.08088

Fluctuation-induced ferrimagnetism in sublattice-imbalanced antiferromagnets with application to SrCu$_2$(BO$_3$)$_2$ under pressure

Pedro M. Cônsoli·Max Fornoville·Matthias Vojta
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Abstract

We show that a collinear Heisenberg antiferromagnet, whose sublattice symmetry is broken at the Hamiltonian level, becomes a fluctuation-induced ferrimagnet at any finite temperature $T$ below the N\'eel temperature $T_{\rm N}$. We demonstrate this using a layered variant of a square-lattice $J_1$-$J_2$ model. Linear spin-wave theory is used to determine the low-temperature behavior of the uniform magnetization, and non-linear corrections are argued to yield a temperature-induced qualitative change of the magnon spectrum. We then consider a layered Shastry-Sutherland model, describing a frustrated arrangement of orthogonal dimers. This model displays an antiferromagnetic phase for large intra-dimer couplings. A lattice distortion which breaks the glide symmetry between the two types of dimers corresponds to broken sublattice symmetry and hence gives rise to ferrimagnetism. Given indications that such a distortion is present in the material SrCu$_2$(BO$_3$)$_2$ under hydrostatic pressure, we suggest the existence of a fluctuation-induced ferrimagnetic phase in pressurized SrCu$_2$(BO$_3$)$_2$. We predict a non-monotonic behavior of the uniform magnetization as function of temperature.

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Pedro M. Cônsoli, Max Fornoville, Matthias Vojta. 2021-05-17. Fluctuation-induced ferrimagnetism in sublattice-imbalanced antiferromagnets with application to SrCu$_2$(BO$_3$)$_2$ under pressure. https://doi.org/10.1103/physrevb.104.064422

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