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An Evans balance, also known as a Johnson Matthey magnetic susceptibility balance, is a scientific instrument used to measure the magnetic susceptibility of solids and liquids. [ 1 ] [ 2 ] Magnetic susceptibility quantifies the extent to which a material becomes magnetized in an applied magnetic field .
When reading, the magnetized material rotates past the heads, the ferrite core concentrates the field, and a current is generated in the coil. In the gap the field is very strong and quite narrow. That gap is roughly equal to the thickness of the magnetic media on the recording surface. The gap determines the minimum size of a recorded area on ...
Schematic diagram of Gouy balance. The Gouy balance, invented by the French physicist Louis Georges Gouy, is a device for measuring the magnetic susceptibility of a sample. . The Gouy balance operates on magnetic torque, by placing the sample on a horizontal arm or beam suspended by a thin fiber, and placing either a permanent magnet or electromagnet on the other end of the arm, there is a ...
When writing, the magnetic medium is heated locally by a laser, which induces a rapid decrease of coercive field. Then, a small magnetic field can be used to switch the magnetisation. The reading process is based on magneto-optical Kerr effect. The magnetic medium are typically amorphous R-Fe-Co thin film (R being a rare earth element).
Micromagnetics is a field of physics dealing with the prediction of magnetic behaviors at sub-micrometer length scales. The length scales considered are large enough for the atomic structure of the material to be ignored (the continuum approximation), yet small enough to resolve magnetic structures such as domain walls or vortices.
This configuration is known as a magnetic tunnel junction (MTJ) and is the simplest structure for an MRAM bit. A memory device is built from a grid of such "cells". The simplest method of reading is accomplished by measuring the electrical resistance of the cell.
In animals, the mechanism for magnetoreception is still under investigation. Two main hypotheses are currently being discussed: one proposing a quantum compass based on a radical pair mechanism, [2] the other postulating a more conventional iron-based magnetic compass with magnetite particles.
Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR, which also sets the foundation for the study of spintronics.
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