Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin orientation and magnetostriction of Tb$_{1-x}$Dy$_{x}$Fe$_{2}$ from
  first principles   The optimal amount of dysprosium in the highly magnetostrictive rare-earth
compounds Tb$_{1-x}$Dy$_x$Fe$_2$ for room temperature applications has long
been known to be $x$=0.73 (Terfenol-D). Here, we derive this value from first
principles by calculating the easy magnetization direction and magnetostriction
as a function of composition and temperature. We use crystal field coefficients
obtained within density-functional theory to construct phenomenological
anisotropy and magnetoelastic constants. The temperature dependence of these
constants is obtained from disordered local moment calculations of the rare
earth magnetic order parameter. Our calculations find the critical Dy
concentration required to switch the magnetization direction at room
temperature to be $x_c$=0.78, with magnetostrictions $\lambda_{111}$=2700 and
$\lambda_{100}$=-430~ppm, close to the Terfenol-D values.

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The categories of this paper are: supr-con
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: hep-th
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The categories of this paper are: physics