A vibrating-sample magnetometer (VSM) (also referred to as a Foner magnetometer) is a scientific instrument that measures magnetic properties based on Faraday’s Law of Induction. Simon Foner at MIT Lincoln Laboratory invented VSM in 1955 and reported it in 1959. [1] Also it was mentioned by G.W. Van Oosterhout [2] and by P.J Flanders in 1956. [3] A sample is first placed in a constant magnetic field and if the sample is magnetic it will align its magnetization with the external field. The magnetic dipole moment of the sample creates a magnetic field that changes as a function of time as the sample is moved up and down. This is typically done through the use of a piezoelectric material. The alternating magnetic field induces an electric field in the pickup coils of the VSM. [4] The current is proportional to the magnetization of the sample - the greater the induced current, the greater the magnetization. As a result, typically a hysteresis curve will be recorded [5] and from there the magnetic properties of the sample can be deduced.
The idea of vibrating sample came from D. O. Smith's [6] vibrating-coil magnetometer.
These allow the VSM to maximize the induced signal, reduce the noise, give a wide saddle point, minimize the volume in between the sample and electromagnet to achieve a more uniform magnetic field at the sample space. [5] The configuration of the coils can vary depending on the type of material being studied. [5]
The VSM relies on Faraday's law of induction, with the detection of the emf given by , [7] where N is the number of wire turns, A is the area, and the angle between the normal of the coil and the B field. However, N and A are often unnecessary if the VSM is properly calibrated. [7] By varying the strength of the electromagnet through computer software, the external field is sweeped from high to low and back to high. [7] Typically this is automated through a computer process and a cycle of data is printed out. The electromagnet is typically attached to a rotating base [7] so as to allow the measurements be taken as a function of angle. The external field is applied parallel to the sample length [7] and the aforementioned cycle prints out a hysteresis loop. Then using known magnetization of the calibration material and wire volume the high field voltage signal can be converted into emu units - useful for analysis. [7]
The precision and accuracy of VSM's are quite high even among other magnetometers and can be on the order of ~ emu. [5] VSM's further allow for a sample to be tested at varying angles with respect to its magnetization letting researchers minimize the effects of external influences. [8] However, VSM's are not well suited for determining the magnetization loop due to the demagnetizing effects incurred by the sample. [8] VSM's further suffer from temperature dependence and cannot be used on fragile samples that cannot undergo acceleration (from the vibration). [5] [7] [8]
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A vibrating-sample magnetometer (VSM) (also referred to as a Foner magnetometer) is a scientific instrument that measures magnetic properties based on Faraday’s Law of Induction. Simon Foner at MIT Lincoln Laboratory invented VSM in 1955 and reported it in 1959. [1] Also it was mentioned by G.W. Van Oosterhout [2] and by P.J Flanders in 1956. [3] A sample is first placed in a constant magnetic field and if the sample is magnetic it will align its magnetization with the external field. The magnetic dipole moment of the sample creates a magnetic field that changes as a function of time as the sample is moved up and down. This is typically done through the use of a piezoelectric material. The alternating magnetic field induces an electric field in the pickup coils of the VSM. [4] The current is proportional to the magnetization of the sample - the greater the induced current, the greater the magnetization. As a result, typically a hysteresis curve will be recorded [5] and from there the magnetic properties of the sample can be deduced.
The idea of vibrating sample came from D. O. Smith's [6] vibrating-coil magnetometer.
These allow the VSM to maximize the induced signal, reduce the noise, give a wide saddle point, minimize the volume in between the sample and electromagnet to achieve a more uniform magnetic field at the sample space. [5] The configuration of the coils can vary depending on the type of material being studied. [5]
The VSM relies on Faraday's law of induction, with the detection of the emf given by , [7] where N is the number of wire turns, A is the area, and the angle between the normal of the coil and the B field. However, N and A are often unnecessary if the VSM is properly calibrated. [7] By varying the strength of the electromagnet through computer software, the external field is sweeped from high to low and back to high. [7] Typically this is automated through a computer process and a cycle of data is printed out. The electromagnet is typically attached to a rotating base [7] so as to allow the measurements be taken as a function of angle. The external field is applied parallel to the sample length [7] and the aforementioned cycle prints out a hysteresis loop. Then using known magnetization of the calibration material and wire volume the high field voltage signal can be converted into emu units - useful for analysis. [7]
The precision and accuracy of VSM's are quite high even among other magnetometers and can be on the order of ~ emu. [5] VSM's further allow for a sample to be tested at varying angles with respect to its magnetization letting researchers minimize the effects of external influences. [8] However, VSM's are not well suited for determining the magnetization loop due to the demagnetizing effects incurred by the sample. [8] VSM's further suffer from temperature dependence and cannot be used on fragile samples that cannot undergo acceleration (from the vibration). [5] [7] [8]
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