Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deviation from the dipole-ice model in the new spinel spin-ice
  candidate, MgEr$_2$Se$_4$   In spin ice research, small variations in structure or interactions drive a
multitude of different behaviors, yet the collection of known materials relies
heavily on the `227' pyrochlore structure. Here, we present thermodynamic,
structural and inelastic neutron scattering data on a new spin-ice material,
MgEr$_2$Se$_4$, which contributes to the relatively under-explored family of
rare-earth spinel chalcogenides. X-ray and neutron diffraction confirm a normal
spinel structure, and places Er$^{3+}$ moments on an ideal pyrochlore
sublattice. Measurement of crystal electric field excitations with inelastic
neutron scattering confirms that the moments have perfect Ising character, and
further identifies the ground state Kramers doublet as having dipolar-octupolar
form with a significant multipolar character. Heat capacity and magnetic
neutron diffuse scattering have ice-like features, but are inconsistent with
Monte Carlo simulations of the nearest-neighbor and next-nearest-neighbor
dipolar spin-ice (DSI) models. A significant remnant entropy is observed as
$T\rightarrow0$~K, but again falls short of the full Pauling expectation for
DSI, unless significant disorder is added. We show that these observations are
fully in-line with what is recently reported for CdEr$_2$Se$_4$, and point to
the importance of quantum fluctuations in these materials.

27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
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The categories of this paper are: eess
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org