Vibration sample magnetometer VSM series is a high-sensitivity magnetic moment measuring instrument based on the principle of electromagnetic induction. The induced voltage generated by the vibration in the detection coil is proportional to the magnetic moment, amplitude and vibration frequency of the sample. On the basis of ensuring that the amplitude and vibration frequency are inconvenient, use a lock-in amplifier to measure this voltage, and then calculate the magnetic moment of the sample to be tested.
Vibration sample magnetometer VSM seriesPrinciple:
If a small sample (which can be approximated as a magnetic dipole) vibrates slightly along the z-axis at the origin, a small coil placed nearby (the axis is parallel to the z-axis) will generate an induced voltage: eg=Gδcosωt=km, where G=π0NA is the geometric factor of the coil, the structure of 74r3VSM, ω is the vibration frequency, δ is the amplitude, m is the magnetic moment of the sample, N and A are the turns and area of the coil. In principle, the relationship between eg and m can be determined by calculation The proportionality coefficient k, so that the magnetic moment of the sample can be obtained from the measured induced voltage. But this kind of calculation is very complicated. In fact, the proportional coefficient k is determined experimentally, that is, by measuring the induced voltage eg of a sample whose magnetic moment is known to be m, k=eg is obtained. This process is called calibration. During the calibration process, the closer the m specific parameters (magnetic moment, volume shape and position, etc.) of the standard sample are to the sample to be measured, the more accurate the calibration will be.
The VSM measurement adopts the open-circuit method. There is a magnetic charge on the surface of the magnetized sample, and the surface magnetic charge generates a demagnetization field NM in the sample (N is the demagnetization factor, which is related to the specific shape of the sample). So in the sample, the total magnetic field is not the magnetic field H generated by the magnet, but H-NM. The measured curve should be corrected by the demagnetization factor, and H should be replaced by H-NM.
The manufacturer of the Vibration sample magnetometer VSM series tells you that the position of the sample has an impact on the sensitivity of the measurement. The sample moves away from the center along the direction of the two coils (x direction), and the induction signal becomes larger; the other two directions (y and z directions) leave the center, and the induction signal becomes smaller. The position is the minimum value in the x direction and the maximum value in the y and z directions, and is the position where the induction signal is least sensitive to space, called a saddle point. The small area near the point is called the saddle area, and the sample should be placed in the saddle area when measuring, so that the error caused by the finite volume of the sample can be minimized.