Structure-Property Relationship of Ion-Beam Sputtered Nd-Fe-B Magnetic Thin Films On (111) Silicon
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MAGNETIC THIN FILMS ON (111) SILICON
ANTHONY S. NAZARETH, HARSH DEEP CHOPRA*, D.K. SOOD AND R. B. ZMOOD, Dept. of Electrical Engineering, Royal Melbourne Institute of Technology, 124 La Trobe Street, Melbourne 3000, Australia.
*Dept. of Materials Engineering, Monash University, Clayton, Victoria 3168, Australia. ABSTRACT A focussing grid broad beam Kaufmnan source, using argon ions on a target of nominal
composition Nd 2FeI 4B has been employed to sputter deposit magnetic thin films of thicknesses ranging from 800 A to 1300 A on silicon-(1 11) substrates at room temperature. These films were characterised for their composition depth profile by Rutherford Backscattering Spectroscopy, while x-ray diffraction was used to study the crystallographic structure. Due to a close match between (111) Si with (220) Nd2Fe1 4B lattice spacings, preferred crystallographic texturing was expected, and experimental results showed a greatly enhanced (220) texture. The degradation in magnetic properties was attributed to the presence of oxygen in the films as indicated by concentration depth profiles. It is premised that another significant role of oxygen may be to relieve the misfit strain across the interface by its incorporation within the Nd 2Fel 4B phase.
INTRODUCTION In recent years the Rare Earth-Transition Metal (RE-TM) permanent magnet systems like neodymium-iron-boron (Nd-Fe-B) [1,2], samarium-cobalt (Sm-Co) [3,4], and neodymiumiron-titanium (Nd-Fe-Ti) [5] have attracted attention because of their high coercivities, high remanent moments, and high maximum energy products. Such properties make them an ideal choice for generating higher efficiencies for a given volume of the magnetic thin film. The high remanent moments and high coercivities of sputter synthesised films allow new small scale permanent magnet arrays to be fabricated. In an increasing number of device applications, such as magnetic actuators, micro-machines, etc., it is being required that such films be compatible with the existing IC technology. This has spurred the need to directly deposit magnetic thin films on silicon substrates, since it is the material of choice in IC technology. In the RE-TM Nd-Fe-B magnetic thin films, the magnetic phase, Nd2Fel 4B has a tetragonal symmetry, with c/a ratio greater than one. These magnetic films exhibit uniaxial magnetocrystalline anisotropy which is responsible for the special magnetic properties. Special anisotropic behaviour is a result of the preferential alignment of the c-axis either in or out of the film plane during growth. In the Nd-Fe-B system with c/a>l, the demagnetisation 511 Mat. Res. Soc. Symp. Proc. Vol. 354 ©@1995 Materials Research Society
energy minimisation favours an in-plane anisotropy. However, both in-plane and perpendicular anisotropic behaviour are observed in this system depending on the sputtering conditions [2-6]. Although the Nd-Fe-B thin films have been grown by several sputtering techniques (rfsputtering, dc-magnetron sputtering, thermalised rf sputtering, etc.), we have found no evid
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