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An induction hysteresigraph using 50 Hz sine wave fields of 7 kOe maximum amplitude, generated by a solenoid-type multilayer coil, suitable for small amounts (down to tens of milligram) of magnetic materials is proposed. The changes in field and magnetization are detected by a field sensing coil and a compensated pick-up coil system, respectively, the as-induced signals being processed by two analog measuring channels (channel H and channel M), whose output signals reproduce the time evolution H(t) and M(t) of the two quantities. These signals are recorded via PC-assisted analog-to-digital conversion and then subjected to final numerical correction and calibration; apart from the demagnetizing field correction, the possible errors caused by the stray flux generated by the magnetized sample itself are also taken into account. In addition, instead of weak signals denoising via standard filtering or smoothing algorithms, reconstruction based on flexible combinations of transition-type fitting functions of time periodic argument is proposed. To prevent signal waveform distortions that can be caused by the frequency-dependent response of channel M, a thorough analysis is carried out in the time domain, by simulating the run of a 100 kHz bandwidth severe test signal, across the stages of this channel. This signal consists of sharp ac pulses, built as a digital replica of the electromotive force induced in a pick-up coil containing the sample, during its evolution along a steep-sided hysteresis loop; an original method, using a small number of parameters, is proposed to build the spectral expansion of the test signal. [ABSTRACT FROM AUTHOR]

Two effects must be considered for the purpose of comparing hysteresis loops of hard magnetic materials (e.g., Nd–Fe–B magnets), measured in open circuit (e.g., vibration sample magnetometer or extraction magnetometer) to those measured in closed circuit (i.e., in a hysteresigraph). The first of these is related to the influence of magnetic viscosity during magnetization reversal, which reduces coercivity. Due to longer measurement times with magnetometers compared to hysteresigraphs (typically 100 s versus 1 s), the coercive field is reduced more in open-circuit measurements than in closed-circuit ones, by typically 20 kA/m. The second effect to be considered is due to differences in various contributions to the demagnetizing field. The slope of the magnetization variation in open-circuit loops is different to that due to the usually considered demagnetizing effects (applicable to soft materials). A reduction in the open-circuit coercive field value compared to the closed-circuit one is found, which is of the order of 25 kA/m for the systems discussed here. This is attributed to the fact that the reversal process itself is affected by how the measurement is made. Reversal has less collective character during open-circuit than during closed-circuit measurements. [ABSTRACT FROM AUTHOR]

Presents information on a study which developed a large bore pulsed field hysteresigraph system used for characterizing permanent magnets. Significance of pulse field magnetometer; Description of the system; Procedure of calibration; Tests conducted on the system; Conclusion.