## Abstract

We present temperature dependent magnetic neutron diffraction measurements on Ba(Fe_{1-x}Co_{x})_{2}As_{2} for x=0.039, 0.022, and 0.021 as-grown single crystals. Our investigations probe the behavior near the magnetic tricritical point in the (x,T) plane, x_{tr}≈0. 022, as well as systematically exploring the character of the magnetic phase transition across a range of doping values. All samples show long-range antiferromagnetic order that may be described near the transition by simple power laws, with β=0.306±0.060 for x=0.039, β=0.208±0. 005 for x=0.022, and β=0.198±0.009 for x=0.021. For the x=0.039 sample, the data are reasonably well described by the order parameter exponent β=0.326 expected for a three-dimensional Ising model while the x=0.022 and x=0.021 samples are near the β=0.25 value for a tricritical system in the mean-field approximation. These results are discussed in the context of existing experimental work and theoretical predictions.

Original language | English |
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Article number | 134507 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 87 |

Issue number | 13 |

DOIs | |

State | Published - Apr 9 2013 |

Externally published | Yes |

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