Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Entropy-driven order in an array of nanomagnets   Long-range ordering is typically associated with a decrease in entropy. Yet,
it can also be driven by increasing entropy in certain special cases. We
demonstrate that artificial spin ice arrays of single-domain nanomagnets can be
designed to produce entropy-driven order. We focus on the tetris artificial
spin ice structure, a highly frustrated array geometry with a zero-point Pauli
entropy, which is formed by selectively creating regular vacancies on the
canonical square ice lattice. We probe thermally active tetris artificial spin
ice both experimentally and through simulations, measuring the magnetic moments
of the individual nanomagnets. We find two-dimensional magnetic ordering in one
subset of these moments, which we demonstrate to be induced by disorder (i.e.,
increased entropy) in another subset of the moments. In contrast with other
entropy-driven systems, the discrete degrees of freedom in tetris artificial
spin ice are binary and are both designable and directly observable at the
microscale, and the entropy of the system is precisely calculable in
simulations. This example, in which the system's interactions and ground state
entropy are well-defined, expands the experimental landscape for the study of
entropy-driven ordering.

15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol