Abstract
We present a high-field study of the strongly anisotropic easy-plane square lattice S=2 quantum magnet Ba2FeSi2O7. This compound is a rare high-spin antiferromagnetic system with very strong easy-plane anisotropy, such that the interplay between spin level crossings and antiferromagnetic order can be studied. We observe a magnetic field-induced spin level crossing occurring within an ordered state. This spin level crossing appears to preserve the magnetic symmetry while producing a nonmonotonic dependence of the order parameter magnitude. The resulting temperature-magnetic field phase diagram exhibits two dome-shaped regions of magnetic order overlapping around 30 T. The ground state of the lower-field dome is predominantly a linear combination of |Sz=0) and |Sz=1) states, while the ground state of the higher-field dome can be approximated by a linear combination of |Sz=1) and |Sz=2) states. At 30 T, where the spin levels cross, the magnetization exhibits a slanted plateau, the magnetocaloric effect shows a broad hump, and the electric polarization shows a weak slope change. We determined the detailed magnetic phase boundaries and the spin level crossings using measurements of magnetization, electric polarization, and the magnetocaloric effect in pulsed magnetic fields to 60 T. We calculate these properties using a mean-field theory based on direct products of SU(5) coherent states and find good agreement. Finally, we measure and calculate the magnetically induced electric polarization that reflects magnetic ordering and spin level crossings. This multiferroic behavior provides another avenue for detecting phase boundaries and symmetry changes.
| Original language | English |
|---|---|
| Article number | 144427 |
| Journal | Physical Review B |
| Volume | 107 |
| Issue number | 14 |
| DOIs | |
| State | Published - Apr 1 2023 |
Funding
The scientific work at LANL was primarily funded by the LDRD program at LANL. The facilities of the NHMFL are funded by the U.S. NSF through Cooperative Grant No. DMR-1644779, the U.S. DOE, and the State of Florida. Theoretical work at UTK by D.D. and C.D.B. was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC-0018660. R.S. acknowledges support by the G. T. Seaborg Institute Postdoctoral Fellow Program under Project No. 20210527CR. S.D. and A.C. at ORNL were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. M.J. (experimental contribution) acknowledges support by DOE Office of Science B.E.S. project “Science at 100 Tesla.” The work at MPK/POSTECH (sample growth) was supported by Grants No. 2020M3H4A2084418 and No. 2022M3H4A1A04074153, through the National Research Foundation (NRF) funded by MISP of Korea. S.-W.C. was partially supported by the U.S. Department of Energy under Grant No. DOE: DE-FG02-07ER46382.