Adjacent Layer Composition Effects on Fetbco Thin Film Magnetic Properties
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magnetization (Ms), the product of Ms and the coercivity, Hc (energy product, MsHc) at 30 C, the temperature at which the remanent perpendicular magnetization rapidly decreases (Td), and the Curie temperature (Tc). EXPERIMENTAL PROCEDURE Figure 1 schematically illustrates the dual ion beam system used to prepare specimens for this study. A pentagonal prism target carousel allows sequential exposure of up to 5 target materials to the primary beam for deposition. Computer control of the primary ion beam and target carousel facilitates flexible and reproducible thin film deposition. A shutter/shield assembly close to the substrate planetary permits target pre-cleaning prior to deposition and reduces substrate bombardment by specularly reflected primary beam components. The planetary enables uniform coating of four 130 mm diameter disk substrates. A secondary ion source can be used to clean substrates prior to deposition and/or to modify properties of the growing films. The system is cryopumped and has a base pressure in the low 10-8 torr range. All specimens were deposited using a 900 eV Xe+ primary beam; a primary beam current of 225 mA results in an average deposition rate of 3-6 nm/min. Xe working gas pressure in the deposition chamber was 2.5 x 10-4 torr. Polished Si (100) wafers are used as substrates. The 1 x 24 nm specimen structure consists of a = 24 nm thick FeTbCo film sandwiched between two 40 nm thick layers of a particular separator/adjacent layer material. For the otherwise identical 6 x 4 nm structure, the 24 nm FeTbCo layer is divided into six = 4 nm thick sheets by = 3 nm thick separator material layers. The The FeTbCo films were sequentially deposited from an Fe-5.3 at.% Co alloy target and an elemental Tb target. The Fe-Co and Tb deposition times were adjusted to produce a layered structure with the desired composition and a nominal repeat periodicity of 1 nm; the 24 nm thick layers therefore consist of 24 FeCo - Th layer pairs, while each of the 4 nm thick layers contains 4 FeCo - Tb layer pairs. For a given deposition process, the 1 nm repeat period roughly corresponds to the maximum in MsHc vs. layer periodicity for FeTbCo materials [4, 5]. Si, SiC, Si3 N4 , SiO, HfO2 and Y2 0 3 were used as targets for the Substrate Planetary Pimary Beam I .
26.3cm
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Shield
Secondary Source
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Figure 1: Schematic illustration of dual ion beam deposition system geometry. 124
separator materials. No reactive gases were employed during deposition; consequently the resulting films from compound targets comprising volatile constituents (i.e. 0 and N) are likely somewhat deficient in 0 or N relative to the starting target composition. As the exact stoichiometry is unknown, the S/AL materials are referred to as SiNx, HfOx, etc. All but the Si S/AL material targets were formed from hot pressed powder compacts. The Si target was dense polycrystalline material. A Digital Measurement Systems model 1660 VSM was used to measure magnetic properties. M-H hysteresis loops at 30 C were used to dete
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