NON-DESTRUCTIVE MEASUREMENT OF MAGNETOSTRICTION IN THIN FILMS.Thin films of magnetic materials Magnetic materials Materials exhibiting ferromagnetism. The magnetic properties of all materials make them respond in some way to a magnetic field, but most materials are diamagnetic or paramagnetic and show almost no response. deposited on various substrates are of fundamental importance to the magnetic recording industry as well to the operation of microscale actuators. Their magnetostrictive properties must be tailored to the application and are usually measured by depositing the film on one side of a slender, non- magnetic reed. When an external magnetic field is applied, the bending of the reed yields values for the magnetic field dependence of the magnetostriction Magnetostriction The change of length of a ferromagnetic substance when it is magnetized. More generally, magnetostriction is the phenomenon that the state of strain of a ferromagnetic sample depends on the direction and extent of magnetization. coefficient of the film. Drawbacks of this common procedure are that (1) it is destructive in that reed must be fabricated fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: with specific dimensions, (2) the results are characteristic of the entire film, and (3) the material of the substrate may not be the same as that used in the final application. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. is developing an ultrasonic technique that can be applied to a local region of the film on any substrate for application to Combinatorial Libraries of magnetostrictive films. This method employs an ultrasonic wave in the substrate to apply an elastic strain elastic strain A form of strain in which the distorted body returns to its original shape and size when the deforming force is removed. See more at strain. of known wave length and frequency to the film. Since the film is magnetostrictive, it generated a magnetic field above the surface that can be detected by a non-contacting coil held above the film. The magnitude of this field and hence the amplitude of the electrical signal from the coil measures the magnetostrictive coefficient of the film under the coil. An external source of a DC biasing magnetic field allows the magnetic field dependence of the magnetostrictive coefficient to be measured. At present, the ultrasonic wave is introduced by a piezoelectric The property of certain crystals that causes them to produce voltage when a mechanical pressure is applied to them such as sound vibrations. This technique is used to build crystal microphones, phonograph cartridges and strain gauges, all of which turn mechanical movement into voltage. transducer transducer, device that accepts an input of energy in one form and produces an output of energy in some other form, with a known, fixed relationship between the input and output. attached to an edge of the substrate some distance from the sensor coil. In the future, this transducer will be replaced by a coil that uses the film's magnetostriction to generate the ultrasonic wave. Thus, a probe that can be scanned over the surface of a magnetic film on any substrate can be constructed and used to measure local magnetostrictive properties of films on devices. |
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