Thermal properties and Ising critical behavior in EuFe2As2

Specific heat and thermal diffusivity have been studied by means of a high resolution ac photopyroelectric calorimeter in the vicinity of phase transitions in EuFe2As2: the first one corresponding to the ordering of the Fe2+ spins concomitant to a structural transition at 188.1 K and the second one to the antiferromagnetic ordering of the Eu2+ spins at 18.4 K. The weak first order character of the first transition has been confirmed while the critical behavior of the second transition at lower temperature has been established to correspond to the 3D-Ising universality class (αexp = 0.11 ± 0.03). This is in agreement with the proposed uniaxial arrangement of the Eu2+ spins lying along the long orthorhombic axis a as reported in literature.