Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exchange dependent ultrafast magnetization dynamics in
  Fe$_{1-x}$Ni$_{x}$ alloys   Element specific ultrafast demagnetization was studied in Fe$_{1-x}$Ni$_{x}$
alloys, covering the concentration range between $0.1<x<0.9$. For all
compositions, we observe a delay in the onset of Ni demagnetization relative to
the Fe demagnetization. We find that the delay is correlated to the Curie
temperature and hence also the exchange interaction. The temporal evolution of
demagnetization is fitted to a magnon diffusion model based on the
presupposition of enhanced ultrafast magnon generation in the Fe sublattice.
The spin wave stiffness extracted from this model correspond well to known
experimental values.

8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph