I need to under stand What is the difference between Magneto-optical Kerr effect (MOKE) hysteresis loop and vibrating sample magnetometer (VSM) hysteresis loop? and the use of each one of them?
Dear Hisham Hashim
MOKE and VSM are scientific instruments called magnetometers. These can be used to perform magnetization measurements to reveal the magnetic properties of the materials being studied. Here is a summary of both:
The magneto-optical Kerr effect (MOKE) has proved to be a useful research tool for understanding ferromagnetism and magnetic hysteresis. The MOKE occurs when light reflected from the surface of a magnetized material experiences a change in its polarization. Studying this rotation of polarized light provides insights into the magnetic behavior of materials that have potential in future technology to minimize bit storage and improve processing speeds. The MOKE is a simple and popular research tool; however, the diffraction limit of visible light inhibits the study of atomic scale magnetism using this method. To overcome this limitation, Xrays from synchrotron sources around the world are employed to study magnetic properties on a smaller scale. While the use of synchrotron X-rays is much more effective and essential for the ongoing study of magnetism, providing ultrafast imaging of nanoscale dynamics, the MOKE method still serves as an efficient research tool for magnetic materials due to its low cost and simplicity.
A vibrating sample magnetometer (VSM) systems are used to measure the magnetic properties of materials. The vibrating component causes a change in the magnetic field of the sample, which generates an electrical field in a coil based on Faraday’s Law of Induction. If the sample is placed within a uniform magnetic field H, a magnetization M will be induced in the sample. In a VSM, the sample is placed within suitably placed sensing coils, also held at the desired angle. And the vibrating sample component is made to undergo sinusoidal motion, i.e., mechanically vibrated. The electromagnet activates before the testing starts so if the sample is magnetic, it will become more so the stronger the field that is produced. A magnetic field H appears around the sample and, once the vibration begins, then the magnetization of the sample can be analyzed as changes occur in relation to the timing of movement. Because magnetic flux changes induce a voltage in the sensing coils that is proportional to the magnetization of the sample. Changes in the signal are converted to values by the software to graph magnetization M versus the magnetic field H strength, often referred to as a hysteresis loop.
References:
http://article.sapub.org/10.5923.j.ijea.20170701.03.html
Article MOKE hysteresis loop method of determining the anisotropy co...
https://www.lakeshore.com/Documents/Mag%20media%20app%20note.pdf
http://www.microsense.net/products-vsm.htm
Dear Hisham Hashim,
In VSM you probe the bulk magnetic properties of a sample. Wheres in MOKE you probe till the penetration depth of the light in your sample. So it depends upon the nature of the material, its absorption coefficient and the energy of the incident electromagnetic wave.
In MOKE the y axis (Magnetization ) is a normalized quantity, whereas the hysteresis from VSM measurement will give the you absolute magnetization of the sample therefore you can calculate the magnetization per-formula units.
Regards
Edward
Dear Hisham Hashim,
the first two answers are correct. Let me simply summarize:
1) VSM measures the real magnetization of the whole sample. If you know the number of atoms contributing to it, you can divide by it and get the magnetic moments per atom (in case all are equal).
2) MOKE measures the optical rotation of the light, a quantity that is related to the magnetic moments but in a complicated way, difficult to determine. Therefore, the technique is most useful to determine relative changes in the magnetic properties, or other quantities such as the Curie temperature. The optical rotation depends on the wavelength of the light used as probe, and obviously you can only get information about the properties within the penetration depth of the beam.
Regards
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