Title: Quantification of local Ising magnetism in rare-earth pyrogermanates ${\mathrm{Er}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$ and ${\mathrm{Yb}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$

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 m_J component. However, the low point group symmetry of the rare-earth site leads to finite mixing of all other m_J'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 consideringmore » the magnetic excitations in the ordered state. Lastly, 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.« less

Authors:

Pajerowski, Daniel M.  ^[1];

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Taddei, Keith M.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-1468-0823"
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Sanjeewa, Liurukara D. ^[2]; Savici, Andrei T.  ^[1];

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Stone, Matthew B.  ^[1];

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Kolis, Joseph W. ^[3]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Clemson Univ., SC (United States)
3. Clemson Univ., SC (United States)

Publication Date:

2020-01-15

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1606915

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 101; Journal Issue: 1; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY