Intertwined dipolar and multipolar order in the triangular-lattice magnet TmMgGaO4

Yao Shen,Robert Bewley,Astrid Schneidewind,Yayuan Qin,Jun Zhao,Yao-Dong Li,Changle Liu,Shoudong Shen,Gang Chen

doi:10.1038/s41467-019-12410-3

Abstract

A phase transition is often accompanied by the appearance of an order parameter and symmetry breaking. Certain magnetic materials exhibit exotic hidden-order phases, in which the order parameters are not directly accessible to conventional magnetic measurements. Thus, experimental identification and theoretical understanding of a hidden order are difficult. Here we combine neutron scattering and thermodynamic probes to study the newly discovered rare-earth triangular-lattice magnet TmMgGaO4. Clear magnetic Bragg peaks at K points are observed in the elastic neutron diffraction measurements. More interesting, however, is the observation of sharp and highly dispersive spin excitations that cannot be explained by a magnetic dipolar order, but instead is the direct consequence of the underlying multipolar order that is “hidden” in the neutron diffraction experiments. We demonstrate that the observed unusual spin correlations and thermodynamics can be accurately described by a transverse field Ising model on the triangular lattice with an intertwined dipolar and ferro-multipolar order.

Highlights

A phase transition is often accompanied by the appearance of an order parameter and symmetry breaking
The hidden-order phase transition is signaled by the change of bulk properties such as the magnetic susceptibility and heat capacity[14]; but unveiling its microscopic nature is difficult because the hidden-order parameter cannot be directly disclosed by microscopic probes such as neutron diffraction or muon spin rotation/relaxation[11]
We show that the spin correlations and thermodynamics of TmMgGaO4 can be accurately described by the transverse field Ising model with an intertwined dipolar and multipolar order on the triangular lattice

Summary

Introduction

A phase transition is often accompanied by the appearance of an order parameter and symmetry breaking. We combine neutron scattering and thermodynamic probes to study the newly discovered rare-earth triangular-lattice magnet TmMgGaO4. The hidden-order phase transition is signaled by the change of bulk properties such as the magnetic susceptibility and heat capacity[14]; but unveiling its microscopic nature is difficult because the hidden-order parameter cannot be directly disclosed by microscopic probes such as neutron diffraction or muon spin rotation/relaxation[11]. The recent discovered rare-earth magnet TmMgGaO4 may provide a new opportunity to examine the exotic ordering phenomenon of f-electrons[20]. This material has the same crystal structure as the spin liquid candidate tallizes in the R3m space group with.

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Conclusion