Fabrication of thin films for a small alternating gradient field magnetometer for biomedical magnetic sensing applications

摘要

Thin film alternating gradient field magnetometers (AGFM) have potential for measuring magnetic moments of minerals in extraterrestrial soil samples. AGFM sensors offer increased spatial resolution required to detect magnetic nanoparticles for biosensing applications. We have fabricated a patterned thin film with the properties necessary for use in a small AGFM system. Hexagonal-close-packed CoCrPt thin films of 20 and 500 nm were sputtered (nominal composition of Co_(66)Cr_(15)P_(19), showing a high magnetic moment and large out-of-plane anisotropy. The films showed a △θ_(50) of better than 3° for the (002) CoCrPt peak for all films, which improves with thickness. The texture is partly due to the NiW and Ru underlayers. The films showed an out-of-plane easy axis, indicating a strong uniaxial anisotropy that exceeds the shape demagnetization energy. This is due to the addition of Cr, which decreases the magnetic moment of the films; magnetoelas-tic coupling and film stresses may also aid in achieving a perpendicular anisotropy. The first-order uniaxial anisotropy constants were calculated as a function of temperature, ranging from 3.7× 10~6 ergs/cm~3 at room temperature to 6.8× 10~5 ergs/cm~3 at 500 ℃, and the T dependence agrees with Akulov's theory for uniaxial materials. The thickest film was etched with a checkerboard pattern to decrease the demagnetization effects, which are seen more influentially in the thicker films. This opened up the hysteresis loop, and decreased the amount of field necessary to overcome the thin film geometry.