Effect of Critical Spin Fluctuations on the Transport and Magnetic Properties of EuFe2As2 Crystals

Critical magnetic fluctuations in EuFe 2 As 2 crystals have been studied using nonresonant microwave absorption. Analysis of measurements of the resistivity and magnetic susceptibility makes it possible to determine the static critical exponents and has demonstrated that the behavior of the system is described by the two-dimensional Ising model. The dynamic critical exponent z = 1.78 has been found from a theoretical analysis of microwave absorption data, taking into account the static exponents and the scaling relation. This value is consistent with the theoretical value obtained within the two-dimensional Ising model for antiferromagnets. The estimated value z for EuFe 2 As 2 corresponds to universality class A , suggesting the influence of the magnetic subsystem of Eu 2+ ions on the conductivity of the FeAs layers. The application of a magnetic field leads to the tendency to change the character of the fluctuations and weaken the antiferromagnetic coupling, which corresponds to a change in the universality class of the phase transition from A to C .