Study of superconducting properties of polycrystalline layered underdoped pnictide BaFe2−xNixAs2 with x = 0.07

We studied the superconducting energy parameters of underdoped polycrystalline BaFe1.93Ni0.07As2 pnictide with Tc ≈ 18.5 K synthesized via a novel method. Using incoherent multiple Andreev reflection effect spectroscopy, we directly determined the magnitudes of two microscopic superconducting order parameters: the small superconducting gap and a possibly large anisotropic gap in the k-space, their characteristic ratios and temperature dependences. The calculated temperature dependences of the superconducting gaps, calculated using the model written by Moskalenko and Suhl for two effective superconducting condensates fits well with the experimental data. A resonant interaction of the superconducting subsystem with a characteristic bosonic mode has been observed and the boson energy at T << Tc was determined.