The intrinsic radiation and electromagnetic wave reflection coefficient in the range of 8 mm of Ni_2,14Mn_0,81GaFe_0,05 and Ti-Ni alloys in the temperature interval near the phase transitions of the 1st and 2nd order 

I. V. Bychkov¹, V. A. Golunov², D. S. Kalenov², A. P. Kamantsev², D. S. Kuchin², V. V. Koledov², D. A. Kuzmin¹, V. V. Meriacri², S. V. von Gratowski ²,
 M. P. Parkhomenko², A. V. Mashirov², V. G. Shavrov²

¹Chelyabinsk State University,
²Kotelnikov Institute of Radio-engineering and Electronics of RAS

 

The paper is received on December 1, 2014

 

Abstract. The original experimental techniques are created for the study of the electromagnetic response and spontaneous radiation of electromagnetic waves  in the range of 28-32 GHz, of samples of the alloys with phase transitions (PT). Using these techniques, the following experiments were done: there were carried in situ measurements of the electromagnetic waves radiation of a ferromagnetic Heusler alloy Ni_2,14Mn_0,81GaFe_0,05 by radiometry techniques (in the range of 28-32 GHz), and simultaneously  measuring of the low-frequency magnetic susceptibility, reflecting the occurrence of magnetic and structural PTs in the sample. An anomalous no monotonic temperature dependences of the radiation in the temperature range near magneto structural PT of the 1st order (330 - 345 K), and abnormal fluctuations in the radiation near the Curie point (360 K) were detected. The contributions to the signal from the self-radiation of the sample and the reflected electromagnetic radiation from a background were separated. The influence of the nature of the kinetics of PT upon millimeter wave radiation of sample was investigated by changing the rate of heating / cooling from 0.1 K / s to 10 K / s. It was shown that the peaks of the intrinsic radiation increases with the rate of temperature change. These methods confirm that the detected anomalies are not subjected to Planck's formula and the Stefan-Boltzmann law and are associated with non-equilibrium processes at PT. The study by the radiometric technique of the electromagnetic radiation of the TiNi alloy of it’s intrinsic radiation and electromagnetic wave reflection coefficient in the range of 28-32 GHz were done. In the temperature range near the thermoelastic martensitic structural PT (290-315 K) there were revealed the anomalies of the intrinsic radiation and the reflection coefficient which are associated with the non-equilibrium processes at PT. The model is propose that relates the reflection coefficient anomalies and intensity of intrinsic radiation. The results of numerical simulations are in good qualitative agreement with the experimental data.

Keywords: electromagnetic waves, millimeter range, phase transition, shape momery effect, TiNi, Heusler alloys, reflection coefficient, intrinsic radiation, evanescent modes.