Magnetic phase diagram of ErB 4 as explored by neutron scattering

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Abstract
The tetragonal 4 f -electron intermetallic ErB 4 is characterized by strong Ising anisotropy along the tetragonal c axis. The magnetic moments on the erbium sites can be mapped onto a Shastry-Sutherland lattice, resulting in geometrical frustration. At zero magnetic field ErB 4 exhibits collinear columnar antiferromagnetic (CAFM) order below T N = 15.4 K . In the presence of a magnetic field parallel to the c axis, ErB 4 exhibits a plateau at 1 / 2 of the saturation magnetization M S , which arises at a spin-flip transition at H 1 = 1.9 T. Fractional magnetization plateaus and other exotic spin phases are a well-established characteristic feature of frustrated spin systems. Monte Carlo simulations propose that ErB 4 is an ideal candidate to feature a spin supersolid phase in close vicinity of H 1 between the CAFM and M / M S = 1 / 2 plateau (HP) phase. Here, we combine single-crystal neutron diffraction and inelastic neutron scattering to study the magnetic phase diagram and the crystal electric-field (CEF) ground state of ErB 4 . Our measurements as a function of magnetic field find no signature of the spin supersolid phase but allow us to determine the magnetic structure of the HP phase to be of the up-up-up-down (uuud) type consistent with an Ising material. The magnetic moment μ CEF = 8.96 µ B expected from the CEF configuration determined by our inelastic neutron-scattering measurements is also consistent with the ordered moment observed in neutron diffraction, showing that the moments are fully ordered and close to the Er 3 + free ion moment (9.6 µ B ).
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Funding Information
  • Universität Zürich
  • Horizon 2020
  • HORIZON EUROPE Marie Sklodowska-Curie Actions (884104)
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (206021_163997)
  • U.S. Department of Energy
  • Office of Science
  • Basic Energy Sciences
  • Paul Scherrer Institut (2021_0134)

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