Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Tuning the Ultrafast Spin Dynamics in Carrier-Density-Controlled
  Ferromagnets   Ultrafast strengthening or quenching of the ferromagnetic order of
semiconducting Eu1-xGdxO was achieved by resonant photoexcitation. The
modification of the magnetic order is established within 3 ps as revealed by
optical second harmonic generation. A theoretical analysis shows that the
response is determined by the interplay of chemically and optically generated
carriers in a nonequilibrium scenario beyond the three-temperature model.
General criteria for the design of spintronics materials with tunable ultrafast
spin dynamics are given.

24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ