A HIGH-PERFORMANCE HYSTERESIS LOOP TRACER

A high-performance and inexpensive hysteresis loop tracer has been dev eloped to measure quasistatic (0.02 Hz or less) hysteresis loops of so ft ferromagnetic materials. It was applied very successfully to measur e straight pieces of amorphous and nanocrystalline ribbons and amorpho us wires. Especially high-magnetic-field resolution is required when n anocrystalline ferromagnets and amorphous wires are measured. Nanocrys talline materials exhibit very low coercivity (H(c)=0.1-0.5 A/m). The error of H(c) measurement using this tracer does not exceed 0.05 A/m e ven though the amorphous wires have very small cross section (0.008 mm 2). The examples of hysteresis loops measured at low (50 A/m) and high magnetic field ( 14 kA/m) are presented. The apparatus consists of an IBM-compatible computer equipped with 12 bit analog-to-digital and di gital-to-analog converters, bipolar power supply, fluxmeter, solenoid and a pickup coil connected to a compensation coil. This equipment is free of 50 Hz noise, a significant problem in the performance of low-f requency loop tracers. The software was developed to enable measuremen t and immediate display of the M-H hysteresis loop. Previous loops als o can be displayed and printed. Calibration of the setup is also possi ble. In the case of straight samples the measurements are followed by calculation of demagnetization factor N(d)(calc.) using the ellipsoida l approximation of the sample shape. It was found that the experimenta l value of N(d) is 30%-40% of the calculated value N(d)(calc.) for the ribbons studied. Higher values of N(d) correspond to the thicker ribb ons where better agreement was obtained.