Abstract
Recently, a local-Ising-type magnetic order was inferred from neutron diffraction of the antiferromagnetic Er2Ge2O7 (pg-ErGO) with an applied magnetic field. Here, we use neutron spectroscopy to investigate the energetics of pg-ErGO and the isostructural Yb2Ge2O7 (pg-YbGO) to evaluate the adequacy of the local-Ising description. To begin, we generate a model of the magnetic structure of pg-YbGO using neutron diffraction and find a net ferromagnetic moment. While pg-ErGO and pg-YbGO have highly symmetric crystal structures (P41212 tetragonal space group 92) with only one trivalent rare-earth magnetic site, the point symmetry of the rare-earth site is low with only a single symmetry element (point group C1). For both compounds, the energy scale of the first excited state is large compared to the magnetic ordering temperature, suggesting Ising character. The ground-state Kramer's doublet of both compounds is dominated by the maximal mJ component. However, the low point group symmetry of the rare-earth site leads to finite mixing of all other mJ's, which suggests potential deviations from Ising behavior. Moreover, quasielastic scattering is observed deep in the ordered state of pg-ErGO and pg-YbGO that may be due to non-Ising behavior. The dominant magnetic interaction in both compounds is found to be magnetostatic by considering the magnetic excitations in the ordered state. From consideration of these data, the pg-YbGO is more Ising-like than pg-ErGO. Also, quantum multicritical points are anticipated with applied magnetic field in both compounds.
| Original language | English |
|---|---|
| Article number | 014420 |
| Journal | Physical Review B |
| Volume | 101 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 15 2020 |
Funding
D.M.P., K.M.T., A.T.S., and M.B.S. are supported through the Scientific User Facilities Division of the Department of Energy (DOE) Office of Science, sponsored by the Basic Energy Science (BES) Program, DOE Office of Science. L.D.S. is supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Science and Engineering Division. This research used resources at the High Flux Isotope Reactor and Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The material synthesis and crystal growth at Clemson was supported by DOE BES award DE-SC0020071. Andrey Podlesnyak, Steve Nagler, Garrett Granroth, and Mark Lumsden helped to discuss these data. Doug Armitage assisted in design of the sample holder for the CNCS experiment. Todd Sherline operated the refrigerator for the CNCS experiment. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.