Vibrating-sample magnetometer

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. Also it was mentioned by G.W. Van Oosterhout and by P.J Flanders in 1956. 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. 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 and from there we can deduce the magnetic properties of the sample being measured.
The idea of vibrating sample came from D. O. Smith's vibrating-coil magnetometer.
Typical VSM overview:.
Conditions for VSM to be effective:.
Importance of pick-up coils:.
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. The configuration of the coils can vary depending on the type of material being studied.
Relation to Physics:.
The VSM relies on Faraday's law of induction, with the detection of the emf given by formula_1, where "N" is the number of wire turns, "A" is the area, and formula_2 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. By varying the strength of the electromagnet through computer software, the external field is sweeped from high to low and back to high. 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 so as to allow the measurements be taken as a function of angle. The external field is applied parallel to the sample length 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.
Advantages and Disadvantages:.
The precision and accuracy of VSM's are quite high even among other magnetometers and can be on the order of ~ formula_3 emu. VSM's further allow for a sample to be tested at varying angles with respect to it's magnetization letting researches minimize the effects of external influences. However, VSM's are not well suited for determining the magnetization loop due to the demagnetizing effects incurred by the sample. VSM's further suffer from temperature dependence and cannot be used on fragile samples that cannot undergo acceleration (from the vibration).