Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Temperature and field evolution of site-dependent magnetism in
  $\epsilon$-Fe$_2$O$_3$ nanoparticles   8~nm epsilon-Fe2O3 nanoparticles exhibit a spin reorientation transition that
begins at 150 K which is a hallmark of this unique iron-oxide polymorph. We
find that the change from the high to low temperature magnetic structures has
been suppressed by ~50 K. At the spin reorientation temperature, a change of
the field-dependent response of the tetrahedral sites in intermediate field
strengths (0.25 - 1.5 T) indicates that a collective tetrahedral distortion
occurs to which the octahedral sites adjust, altering the magnetic anisotropy.
An abrupt step in the hyperfine parameters' temperature dependencies,
especially at 125 K for the hyperfine field associated with the Fe4 tetrahedral
sites, suggests strongly a change in the superexchange pathways are responsible
for the spin reorientation.

26
The categories of this paper are: bayes-an
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol