This device is used to determine the magnetization in our samples. When the sample is placed in a uniform magnetic field, a dipole moment proportional to the product of the sample susceptibility times the applied field is induced in the sample. If the sample is allowed to vibrate sinusoidallly, an electrical signal can be induced in suitably located stationary pick up coils. This signal which is at the vibration frequency is proportional to the magnetic moment, vibration amplitude and vibration frequency. This means, of producing an electrical signal related to the magnetic properties of a sample material is used in the model 4500 VSM. The material under study is contained in a sample holder, which is centered in the region between the pole pieces of an electromagnet. A slender vertical sample rod connects the sample holder with a transducer assembly located above the magnet, which in turn supports the transducer assembly by means of sturdy adjustable support rods.
The transducer converts a sinusoidal ac drive signal provided by a circuit located in the console in to a sinusoidal vertical vibration of the sample rod and the sample is thus made to undergo a sinusoidal motion in a uniform magnetic field. Coils mounted on the pole pieces of the magnet pick up the signal resulting from the sample motion. This ac signal at the vibrating frequency is proportional to the magnitude of the moment induced in the sample. However, it is also proportional to the vibration amplitude and frequency. A servo system maintains constancy in the drive amplitude and frequency so that the output accurately tracks the moment level without degradation due to variation in the amplitude and frequency of vibration.
This technique depends on the ability of a vibrating capacitor located beneath the transducer to generate an ac control signal, which varies solely with the vibration amplitude and frequency. This signal, which is at the vibration frequency, is fed back to the oscillator where it is compared with the drive signal so as to maintain a constant drive output. It is also phase adjusted and routed to the signal demodulator where it functions as the reference drive signal. The signal originating from the sample in the pick up coils is then buffered, amplified and applied to the demodulator. Then it is synchronously demodulated with respect to the reference signal derived from the moving capacitor assembly. The resulting dc output is an analog of the moment magnitude alone, uninfluenced by vibration amplitude changes and frequency drifts. A cryogenic setup attached to the sample permits the low temperature studies.
The transducer converts a sinusoidal ac drive signal provided by a circuit located in the console in to a sinusoidal vertical vibration of the sample rod and the sample is thus made to undergo a sinusoidal motion in a uniform magnetic field. Coils mounted on the pole pieces of the magnet pick up the signal resulting from the sample motion. This ac signal at the vibrating frequency is proportional to the magnitude of the moment induced in the sample. However, it is also proportional to the vibration amplitude and frequency. A servo system maintains constancy in the drive amplitude and frequency so that the output accurately tracks the moment level without degradation due to variation in the amplitude and frequency of vibration.
This technique depends on the ability of a vibrating capacitor located beneath the transducer to generate an ac control signal, which varies solely with the vibration amplitude and frequency. This signal, which is at the vibration frequency, is fed back to the oscillator where it is compared with the drive signal so as to maintain a constant drive output. It is also phase adjusted and routed to the signal demodulator where it functions as the reference drive signal. The signal originating from the sample in the pick up coils is then buffered, amplified and applied to the demodulator. Then it is synchronously demodulated with respect to the reference signal derived from the moving capacitor assembly. The resulting dc output is an analog of the moment magnitude alone, uninfluenced by vibration amplitude changes and frequency drifts. A cryogenic setup attached to the sample permits the low temperature studies.
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