Understanding hidden magnetic phases
27 Oct 2020





​​​Measured and calculated momentum dependence of the spin excitations in TmMgGaO4 at the indicated energies and T = 0.05 K. a–f Raw contour plots of the constant energy images at T = 0.05 K. The signals near Q = (0, 0, 0) in a are due to the elastic contamination from the sample environment close to the direct beam. g–l Calculated spin excitations using the model specified in the text. The dashed lines indicate the zone boundaries. The measurements were performed on LET spectrometer with Ei = 4.8 meV. The color bars indicate scattering intensity in arbitrary unit in linear scale.​  


Some magnetic materials show hidden order phases, where the order parameters are not observed using conventional magnetic measurements. The hidden order phase transition is usually accompanied by changes in the bulk properties such as heat capacity, but identification and understanding the phases is very difficult when they cannot be observed microscopically.

This study focusses on the recently discovered rare-earth triangular-lattice magnet TmMgGaO4. Bulk measurements show that a phase transition occurs at low temperature, but this is the first study to look at the microscopic measurements. The researchers used neutron scattering and thermodynamic measurement​s to study the phase transitions and spin correlations of single crystals of TmMgGaO4.

They observed clearly in the elastic neutron diffraction patterns that the longitudinal component of the effective spins is dipolar. However, they also observed spin excitations that were not present in the elastic diffraction patterns, corresponding to the transverse components. Their calculations demonstrate that this behaviour can be described by a transverse field Ising model on the triangular lattice, with an intertwined dipolar and ferro-multipolar order.

Reproduced from DOI: 10.1038/s41467-019-12410-3 

Instrument: LET

Related publicationIntertwined dipolar and multipolar order in the triangular-lattice magnet TmMgGaO4. Nat Commun 10, 4530 (2019).


Funding: Innovation Program of Shanghai Municipal Education Commission, the Ministry of Science and Technology of China, the National Key R&D Program of the MOST of China and Hong Kongs Research Grants Council.

AuthorsY Shen, C Liu, Y Qin, S Shen (Fudan University), Y Li (Fudan UniversityUniversity of California Santa Barbara), R Bewley (ISIS)A Schneidewind (Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ)), G Chen (The University of Hong KongFudan UniversityNanjing University), J Zhao (Fudan University, Nanjing University) 

Contact: Gianchandani, Shikha (STFC,RAL,ISIS)