Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First order transition and phase separation in pyrochlores with
  colossal-magnetoresistance   Tl$_{2}$Mn$_{2}$O$_{7}$ pyrochlores present colossal magnetoresistance (CMR)
around the long range ferromagnetic ordering temperature (T$_{C}$). The
character of this magnetic phase transition has been determined to be first
order, by purely magnetic methods, in contrast to the second order character
previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The
highest CMR effect, as in Tl$_{1.8}$Cd$_{0.2}$Mn$_{2}$O$_{7}$, corresponds to a
stronger first order character. This character implies a second type of
magnetic interaction, besides the direct superexchange between the Mn$^{4+}$
ions, as well as a phase coexistence. A model is proposed, with a complete
Hamiltonian (including superexchange and an indirect interaction), which
reproduce the observed phenomenology.

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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph