Tailoring of magnetic properties of giant magnetoresistance spin valves via insertion of ultrathin non-magnetic spacers between pinned and pinning layers

Two-dimensional arrays of vertically packed spin-valves with picoTesla sensitivity at room temperature

A new device architecture using giant magnetoresistive sensors demonstrates the capability to detect very low magnetic fields on the pT range. A combination of vertically packed spin-valve sensors with two-dimensional in-plane arrays, connected in series and in parallel, delivers a final detection level of 360 pT/[Formula: see text] at 10 Hz at room temperature. The device design is supported by an analytical model developed for a vertically packed spin-valve system, which takes into account all magnetic couplings present. Optimization concerning the spacer thickness and sensor physical dimensions depending on the number of pilled up spin-valves is necessary. To push the limits of detection, arrays of a large number of sensing elements (up to 440,000) are patterned with a geometry that improves sensitivity and in a configuration that reduces the resistance, leading to a lower noise level. The final device performance with pT detectivity is demonstrated in an un-shielded environment suitable for detection of bio-signals.

Effect of Annealing on the Structural, Magnetic, Surface Energy and Optical Properties of Co32Fe30W38 Films Deposited by Direct-Current Magnetron Sputtering

In this study, a 10–50 nm Co32Fe30W38 alloy thin film sputtered on glass substrates was annealed at different temperatures for 1 h including room temperature (RT), 300, 350, and 400 °C. The structure, magnetic properties, surface energy, and optical properties of the Co32Fe30W38 alloy were studied. X-ray diffraction (XRD) patterns of the as-deposited Co32Fe30W38 thin films showed the amorphous structure. The apparent body-centered cubic (BCC) CoFe (110) structure was exhibited after 300 °C annealing for 1 h. The 300 °C annealed Co32Fe30W38 thin film showed the highest CoFe (110) peak compared with other temperatures. Furthermore, the thicker the Co32Fe30W38 thin film, the higher the CoFe (110) peak. The CoFe (110) peak revealed magneto-crystalline anisotropy, which was related to the strong low-frequency alternative-current magnetic susceptibility (χac) and induced an increasing trend of saturation magnetization (Ms) as the thickness (tf) increased. Due to the thermal disturbance, the χac and Ms for the 350 and 400 °C annealed Co32Fe30W38 thin film decreased. The contact angles of the Co32Fe30W38 thin films were less than 90°. For all temperatures, the surface energy increased when the film thickness increased from 10 to 50 nm. In addition, the surface energies for annealed samples were comparatively higher than the as-deposited samples. The higher surface energy of 28 mJ/mm2 was obtained for the 50 nm Co32Fe30W38 thin film annealed at 300 °C. The transmittance percentage (%) of the as-deposited Co32Fe30W38 film was higher than other annealed conditions. This result contributed to the fact that higher crystallization, due to perfect band structures, may inhibit the transmission of photon signals through the film, resulting in low transmittance and high absorption.