## 2 Experimental Setup, Methods, and Procedures
### Measurement of the Intrinsic Magnetic Field  
The setup for investigating the relatively weak magnetic fields of the prepared samples consists of a defined measuring apparatus, shown in Figure 3.  
Figure 3: The intrinsic magnetic field of the sample measurements: (**a**) diagram of the connection of measuring equipment (1: material specimen, 2: XYZ positioning system, 3: fluxgate sensor, 4: lock-in amplifier, 5: digital acquisition card, 6: PC workstation, 7: LabVIEW and MATLAB console, 8: XYZ stage controller, 9: synchronization device, 10: PTFE table, 11: EM-shielded chamber); (**b**) realization of the experiments in laboratory of electromagnetic nondestructive evaluation, University of Zilina. Figure 2: Measuring instruments used to examine the samples (mechanical testing laboratory, department of material engineering): (**a**) Zwick/Roell ZH\(\upmu\) micro-hardness tester; (**b**) Vickers manual hardness tester; (**c**) tear-off measuring device. The samples were measured in a chamber designed to shield electromagnetic interference using a single-axis fluxgate sensor to detect weak magnetic fields. The sensor can detect magnetic field values in the 0 to 3.4 kHz frequency range and convert them into a DC electric voltage signal, as seen in Figure 4. Its response is linear within the measuring range, and it can distinguish the orientation of the magnetic field. When measuring the intrinsic magnetic field of the samples, a fluxgate sensor positioned on a printed circuit board alongside other electronic circuits sensed the DC component within the specified frequency range. It was powered by a constant 5 V DC voltage source, drawing approximately 25 mA of current during the measurement process. The lock-in amplifier Signal Recovery DSP 7280 (Ametek, Inc., Berwyn, PA, USA) was a selective voltmeter to filter out valuable signals. The filtered signal from the fluxgate sensor was then transmitted to the analog input of the acquisition card and processed using LabVIEW 2014 virtual instrumentation software (National Instruments, Austin, TX, USA). A program block was created in the virtual instrumentation environment to manipulate the signals, store data, and execute other necessary actions. This interface also produced control commands for a three-axis linear manipulator to which the fluxgate sensor was connected. The measurement was conducted in an EM-shielded space using a linear three-axis manipulator (Velmex Inc., New York, NY, USA) to which the sensor was attached, as seen in Figure 5a. The manipulator arm utilizes stepper motors and a threaded rod, providing a resolution of 1.2 \(\upmu\)m on each axis, enabling precise positioning. This setup allows for the construction of a spatial map of the magnetic field near the samples under investigation. The scanning procedure in the region of interest (ROI) involved positioning the sample in the center of a 50 mm \(\times\) 50 mm area, as depicted in Figure 5b. The samples' magnetic field was scanned using a technique called comb scanning. Data from the sensor were recorded as they moved in the \(y\)-axis direction, with 1000 readings taken for each scan line. The spacing between individual scanning lines was fixed at \(\Delta x\) = 0.5 mm. This means that 100 scan lines were recorded for each scan setup of one sample area, representing one complete scan cycle. After each cycle, the sensor was returned to the initial (reference) position, and the measured data were saved in a *.CSV format file. All examined samples were subjected to a non-contact evaluation, focusing on the repeatability of each measurement. Each sample was measured from both of its identical sides (faces), which were labeled L (left side) and R (right side). The experimental measurement conditions from both opposite surfaces were essentially the same. The fluxgate sensor was consistently positioned above the sample at a fixed distance from the surface; \(h\) = 1.4 mm.