Comparative measurement of residual stresses with the method based on the magnetic Barkhausen noise and the relaxation method
For an efficient prediction of residual stresses in a material or a machine part the non-destructive method based on the magnetic Barkhausen noise is, among others, employed in practice. An experimental system developed at home and including measuring and assessment units has proved to be very efficient in various applications of surface hardening or cold hardening, and heat treatment.
The influence of product thickness on the measurements by Barkhausen Noise method
Purpose: The aim of this paper is to show how varying cross section thickness of tested product and calibration sample can depend on results of the residual stress measurements by the Barkhausen Noise method. Design/methodology/approach: The Barkhausen noise parameters as RMS value and total number of Barkhausen pulses in samples with different thickness was measured and compared. Also influence of the frequency and intensity of the magnetization current was analysing. Findings: The significant indirect influence of various cross-section thicknesses on Barkhausen Noise level was pointed. The equations describing influence of the thickness on Barkhausen noise at different magnetization current parameters were found. Research limitations/implications: Also the influence of the differences in width of the calibration sample and tested product was observed but in this research was not analysed. Practical implications: Taking into consideration obtained results lets compensate analytically indirect influence of geometrical factors and magnetization parameters on Barkhausen noise parameters. Originality/value: Original value of this paper is demonstrating significant source of error during residual stress measurements by Barkhausen method. For this moment this fact were not taken into consideration.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.