Ultrasonic and microwave investigation of the structural and magnetic transitions in CaFe2As2 and BaFe2As2 single crystals

Mario Poirier, Maxime Bilodeau, Simon Lefebvre, Amar B. Karki, and Rongying Jin
Phys. Rev. B 89, 155129 – Published 22 April 2014

Abstract

Pulsed ultrasonic experiments performed on the parent compounds of FeAs based superconductors AFe2As2 (A=Ba, Ca) revealed elastic anomalies that agree with a two-step process for the structural/magnetic transitions. Upon cooling, a pronounced velocity softening of longitudinal phonons propagating along the c axis is observed at the structural transition Ts due to a distortion of the lattice. Below a slightly lower temperature TN, a biquadratic coupling between the distortion and an antiferromagnetic order parameter produces a steep velocity stiffening upon further cooling, the stiffening being five times larger in CaFe2As2 than in BaFe2As2. Microwave resistivity measurements at 16.5 GHz suggest that, upon cooling, the lattice distortion at Ts is driven by magnetic fluctuations in BaFe2As2, while it is rather due to lattice fluctuations in CaFe2As2. This suggestion appears consistent with a second-order character of the transitions in BaFe2As2 and a first-order one in CaFe2As2.

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  • Received 25 February 2014
  • Revised 7 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.155129

©2014 American Physical Society

Authors & Affiliations

Mario Poirier, Maxime Bilodeau, and Simon Lefebvre

  • Regroupement Québécois sur les Matériaux de Pointe, Département de Physique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1

Amar B. Karki and Rongying Jin

  • Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA

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Issue

Vol. 89, Iss. 15 — 15 April 2014

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