PINNING MAGNETIZATION BY A SPECIAL THIN-FILM DEPOSITION TECHNIQUE.When materials are deposited onto substrates to make thin films, the usual goal is to produce a smooth deposit. However, recent work at 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. has shown that rough deposits can have some special advantages. In particular, when the incoming flux of atoms strikes the substrate at an oblique angle, a deposit is formed with a strongly textured surface consisting of parallel ridges and valleys. This structure has some special advantages for the fabrication fabrication (fab´rikā´sh  n),n the construction or making of a restoration. of magnetic thin-film devices. In the NIST work, it was found that a thin layer of tantalum tantalum (tăn`tələm) [from Tantalus], metallic chemical element; symbol Ta; at. no. 73; at. wt. 180.9479; m.p. 2,996°C;; b.p. 5,400±100°C;; sp. gr. 16.65 at 20°C;; valence +2, +3, +4, or +5. , obliquely deposited, has a textured roughness that can have a strong effect on a magnetic layer deposited on top of it. The textured surface pins the magnetization direction in the magnetic material, producing a magnetic anisotropy Magnetic anisotropy is a property in an individual atom. It's fundamental measurement has important technological consequences because it determines an atom's ability to store information. . Such pinning of the magnetic direction is needed for the functioning of a special structure known as a spin valve A spin valve is a device consisting of two or more conducting magnetic materials, that alternates its electrical resistance (from low to high or high to low) depending on the alignment of the magnetic layers, in order to exploit the Giant Magnetoresistive effect. , which is used in modern read heads of computer hard disks. The pinning is strong enough to prevent reversal of the magnetization direction of the magnetic film, and the pinning remains strong at the elevated temperatures that may be encountered during use. The anisotropy anisotropy /an·isot·ro·py/ (an?i-sot´rah-pe) the quality of being anisotropic. anisotropy (an´āsôt´r produced by obliquely deposited tantalum thin films has a number of desirable properties: it is strong, it is uniform, and it has good thermal stability. In addition, the system has good corrosion resistance and chemical compatibility. These properties are advantageous, as the increased demand for sensitivity in read heads has led to higher current densities and hotter operating temperatures, and as read heads become smaller to accommodate narrower recorded tracks. |
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